boiler inspection guideline - neeps - nee …€¦ · · 2017-08-30boiler inspection guideline...

BOILER INSPECTION GUIDELINE

Regardless of the original equipment manufacturer, NEE Process Solutions can offer engineering

know how not only to improve unit performance and reliability but also to eliminate operating and

maintenance problems Boilers of the PC or CFB type.


01/2016 of 70

PURPOSE OF BOILER INSPECTION

The purpose of a Boiler Inspection is to:

Use planned outage time effectively to ensure that unit availability, safe operation and

equipment life is maintained.

Reduce forced outages due to maintenance failures.

Effectively plan outage-required preventative maintenance activities and periodic

replacement of normal wear parts.

A typical boiler inspection will deal with the following component areas:

Waterside

Fireside

Boiler Externals

Fuel Firing Equipment

Air/Flue Gas Systems

Auxiliary Equipment

Controls (if necessary)


01/2016 of 70

OUTAGE OBJECTIVES

Major scheduled outage should be structured around customer objectives:

Perform known maintenance tasks.

These items are scheduled based on historical data, past outage inspections or items noted during

the pre-outage operational unit walk down.

Inspect equipment to identify areas needing repairs.

Certain equipment can only be inspected during non-operational periods.

Perform preventive maintenance tasks.

Scheduled or routine maintenance includes such items as turbine bearing inspections, hydrostatic

testing of pressure parts, checking and documenting tube minimum wall thickness, packing valves,

etc.

Upgrade equipment and make design changes as part of a plant betterment program.

Implement state-of-the-art improvements to enhance unit operation and eliminate generic design

problems identified by the manufacturer.

Establish a maintenance history for future use.

This objective is perhaps the most important. It helps reach the goal of all the proceeding objectives

and is required if an ongoing comprehensive maintenance program is to be effective. A maintenance

history is developed by thoroughly documenting the outage and inspection findings for every

scheduled outage.

PERFORMING THE INSPECTION


01/2016 of 70

The boiler inspection identifies and evaluates problem areas (current and potential). This allows the

service engineer to recommend repairs and solutions. The problem areas will have varying levels of

priority.

During an outage, every portion of the unit is thoroughly inspected. The inspection is divided into

three general categories:

The pre-outage walkdown, in which the entire unit and its subsystems are inspected under

operating condition.

The internal inspection of the unit after shutdown and its subsystems

The post-outage start-up inspection in which all the equipment is checked as it is returned to

service.

Inspection activities include visual observations, comparisons, measurements and non-destructive

examination techniques. Accurate record keeping of findings as well as careful labeling of items in

the field will make it easier to communicate punch list items and write the final report. Photographs

are another method to capture and express details.

PRE-OUTAGE WALKDOWN

The pre-outage operational unit walkdown is a significant first-step of the unit inspection. While the

unit is on line, the inspector can assess the operating conditions of the unit and note any

discrepancies that require attention during the outage. Several problem areas are more apparent or

best observed while the unit is still in operation, i.e. safety valve leakage, expansion trams, load-

spring hangers, insulation leakage, etc.

The walkdown should cover the complete unit from top to bottom and all the auxiliary systems.

Auxiliary systems are noted here to demonstrate the scope of a complete unit walkdown.

Structure Components

Boiler Support

Inspect all boiler hanger rods for integrity. Inspect variable load and constant load spring hangers

for loading indications. Note any bottomed-out spring hangers. Also, note any loose hanger rods.

Check all vertical and horizontal buckstays for warpage or misalignment. Inspect all buckstay

stirrups, bolts, nuts, and washers for integrity. Check expansion trams for alignment and note

readings at all reference points with the boiler hot.

Structural Steel

Inspect the structural steel for any interference with the boiler or auxiliary equipment. Inspect the

grating and walkways for missing or loose sections. Check handrails for any missing or broken

sections. Make note of all discrepancies.

Insulation and Lagging

During walkdown, inspect for any areas of missing insulation. Check for discoloration of the

insulation, which would indicate leakage of hot gases or air.


01/2016 of 70

Check duct insulation in areas of expansion joints for signs of buckling. Ensure the presence of

insulation in areas around inspection ports, sootblowers, and access doors. If possible, check areas

of poured refractory for damage. Note all problem areas observed.

Upper Level Components

Safety Valves

Inspect for leakage around the stem or packing. Note if the valve is leaking across the seat so that

some amount of vapor is discharging from the vent piping. Check for pluggage in the drip pan.

Check for binding or interference between the safety valve and vent piping. Make note of abnormal

conditions.

Sootblowers and Furnace Probe

Check for local and remote operation by cycling each sootblower through its operating sequence.

Check for steam leakage in the sootblower supply lines, valves, and swivel tubes. Check the

sootblower wall box for damage. Check the drive mechanism on all sootblowers. Make sure that

cranks and tools are available to retract a sootblower that has stopped in the "advanced" position.

Observe movement of air heater sootblower swivel mechanism. The furnace temperature probe is

usually made by the same manufacturer as the sootblowers and should also be inspected at this

time.

Fuel Components

Ignitors

Operator to remove operating ignitors from service in order to check the indicator lamps on the local

ignitor control station. Have operator place each ignitor in service to verify operation and to check

the indicator lamps. Inspect electrical cables, oil, gas, and air supply lines.

Tilting Tangential Firing System

During walkdown, check the nozzle tilt indicators for degree of tilt indication of the fuel and air

nozzles. Check all overfire air nozzles for degree of tilt. All corners of tilt indicators should be within

5° of each other.

While in this area, inspect all coal piping entering the windbox for wear, damage, or leakage at

elbows or couplings. Also check all fuel pipe hangers. Note the position of all windbox air dampers

as indicated by the scribe mark on the damper shaft. All dampers on the same elevation should be

at the same position. Inspect the windbox and related duct work for leakage.

Oil Guns

The oil guns are located with the fuel and air nozzles in the corners of the furnace. Check all oil and

steam or air lines for leakage; check all related piping and valves; inspect the oil gun advance and

retract mechanism; and check that spare oil guns are properly cleaned and stored.

Coal Piping

Inspect the coal pipes for indications of wear. Check the coal pipe couplings for signs of leakage. If

so equipped, check the coal pipe constant load spring hangers. Examine for any coal pipe related

expansion problems.


01/2016 of 70

Coal Feeders

During the inspection of an operating gravimetric feeder, check the position of the tension pulley,

the feeder belt tracking, and the integrity of the feeder housing. Broken observation windows or

improperly closed doors negate this safety feature of the feeder.

On a C-E volumetric feeder, inspect the drive clutch assembly, the movement of the hinged leveling

gate lever, and the feeder housing. Check the drive motor and gear reducer for unusual noises and

verify proper lubrication levels.

Pulverizers

Inspect the mill foundation for cracks. Check the gear case for proper oil level, temperature, and

signs of leakage. Examine the material being rejected from the mill; excessive coal discharge could

indicate worn or improperly adjusted mill internals. Verify the movement of the three journal

assemblies for uniformity. Inspect the separator body for signs of coal leakage. Make a notation of

the classifier settings; they should all be the same. Inspect the mill motor, filters and foundation.

On exhauster type mills, check the exhauster casing, foundation, and bearing assembly. Check for

excessive noise or vibration from the pulverizer gear housing and exhauster bearing housing.

On pressurized pulverizers, check the gear case and journal seal air systems for leakage or crimped

lines.

Fuel Handling Systems

Inspect all coal handling systems. Note any excessive spillage or accumulation, and check all oil and

gas piping for leakage.

CFB Boiler Limestone Feed System

Inspect the limestone feed system for erosion, loose mounting hardware, proper clearances and

binding of rotating equipment. Note any excessive spillage or accumulation, and check all oil and gas

piping for leakage.

Auxiliary System Components

Air Preheaters

Inspect the upper and lower bearing assemblies. Check oil level and for oil leakage. Listen for any

loud noise, which might indicate problems with the air preheater seals. Check the drive motor and

gear reducer for signs of oil leakage, and verify the operation of the air preheater sootblowers.

Fans/Air and Gas Ducts

Check for the following: foundation cracks or loose anchor bolts, vibration meters for excessive fan

or motor vibration, motor amp readings, and bearing temperatures. Inspect fan housings for

damage and check all air and gas ducts for leakage, expansion problems, and missing insulation.

Ash Removal Systems

Inspect all piping for leakage and pluggage.


01/2016 of 70

Boiler Water Circulating Pumps

Inspect motor and related piping for leakage. Check the pump suction and discharge pressures.

Check and record motor cooling water temperatures. Compare data to normal operating conditions.

Note abnormal conditions.

Pre-boiler Systems

Check all components and piping for leakage. Check all components for any missing insulation.


01/2016 of 70

INTERNAL INSPECTION – WATER SIDE PRESSURE PARTS

The internal inspection requires unit downtime. Lots of maintenance activity is also scheduled

during the outage. The internal inspection activity is complex and covers a large work area.

This section covers only the water-side pressure parts of an inspection plan.

Steam Drum and Internals

Examine the steam/water separating equipment. Inspect the turbo separators, both the primary

and secondary stages. Look for corrosion, deposits, erosion, missing parts, etc. Examine the

condition of the corrugated plate dryers and the return piping.

During inspection:

Check the condition of the seal around the manway door.

Check the area around the inside of the manway door.

Check the interior of the drum for corrosion and deposits.

Check the condition and mounting of the chemical feed pipe, the blowdown pipe, and the

feedwater distribution header.

Check the downcomer nozzles, screens, and vortex eliminators.

Check all drum internals for wear and fit.

Thoroughly examine the drum liners for cracks. Cracks in the liner will allow boiler water to bypass

the steam separation equipment and allow the carryover of suspended solids into the superheater.

Lower Waterwall Drums

During inspection, crawl through the drum checking for cracks or crack-like indications particularly

around nozzle welds and manway access doors.

Generally, these cracks are shallow, not much deeper than 1/32". Usually found on the wetted

surfaces of the drum is a corrosion indication, which could play a part in promoting a crack

penetration.

If cracks or crack-like indications are found, determine the depth by a number of spot grindings.

Information on the depth together with the specific location of the cracks will permit calculations to

be made to determine whether the remaining material thickness is sufficient to meet the

requirements of the ASME Boiler Code for New Boiler Design and Construction.


01/2016 of 70

Potential Cracking Sites


01/2016 of 70

During inspection, check the screens or strainers located in the drum. These screens prevent foreign

material from plugging the orifices. The screens must be intact and firmly secured in place. If any

large holes have developed in the screens, recommend that they be replaced.

Typical Lower Drum Arrangement

Check the locating pin, orifice clamp, and fastener for deterioration, fit, and tightness. Check for

gaps between the orifice adapter and header counter bore. If gaps are found, the adapters may

need to be replaced, repositioned, or repaired.

Check the diameter of the furnace wall supply tube orifices using "Go/No Go" gages. If an orifice is

found to be worn, that is, the opening is enlarged, recommendation should include replacement.

The orifice plates assure that each tube circuit gets an adequate flow depending on its location in

the furnace. Orifices are numbered for reference and have indexing holes so they cannot be

incorrectly placed. Orifices could be either fouled or plugged with deposits, or enlarged by wear or

corrosion. If the orifice is fouled, that is, the opening restricted, recommendations include cleaning

during the outage (if possible) or replacing. Check the orifice mounting and locating pins, and the

clamp and fasteners for signs of deterioration and looseness. Inspect the orifice adapter for signs of

bypassing flow. If problems are found, recommendations might include replace, reposition, or repair

the adapter.


01/2016 of 70

Headers

To perform an internal examination, remove the handhole inspection ports on the header. Examine

the interior for corrosion, deposits, or any other foreign material. Check the area around the

handhole for any signs of cracking. Check the handhole port seal.

During an external examination, visually check the entire header for corrosion, erosion, etc. Visually

check the header nipple welds for signs of cracking. Note cracking and make recommendations for

repair.

Header Inspection

If the header is insulated or covered with refractory, note the condition.

Also inspect all other welds, especially for different material welds (DMW), near the header. If any

cracking is found, determine depth and location, and consult Engineering for recommended repairs.


01/2016 of 70

Inspect the area around each header for signs of potential problems. Inspect the area where a

header penetrates a wall or floor for cracks or expansion problems.

Check all hanger rods for tightness. Also check condition of hanger rods, clevises, and clevis pins for

bowing, overheating, and damage. Hanger rods are made of a tempered material and should not be

cut and rewelded. If significantly damaged recommendation should include replacement.

The combined circulation units are supplied with orificed waterwall inlet headers that can be

internally inspected if the handhole caps are removed. These headers should be checked for

cracking, deposits (especially on the orifices), loose marmon clamps, and cracking between the

internal partition plates and the ID of the header. Header cleanliness is a must.


01/2016 of 70

INTERNAL FIRE-SIDE FURNACE INSPECTION

The second part of the internal inspection is the fire-side (gas-side) or furnace inspection. Again, this

is a large area to inspect, with complex components. This section is divided into component

sections.

Bottom Hopper Area – PC Boiler

The coutant sloped bottom tubes and the bottom ash hopper comprise the lower furnace area.

Inspect casing, plates, screens, and the structural condition of expansion and support members.

Remove all debris, bottom ash, and water remaining in the hopper enclosures. Examine the water

seal trough material and structural condition. Inspect trough for corroded and deteriorated lining

and structural support. Look closely at all welds for signs of cracking and indication of expansion

problems.

Examine the seal plate for indications of corrosion, deterioration, and cracks in the surface.

Inspect splash screen for tears and holes in screen material. Examine all support structures for

indication of expansion problems. Inspect for signs of corrosion and deteriorating conditions.

Inspect drip shield for signs of erosion or corrosion.

The attachment welds securing the drip shields to the waterwall tubes should be inspected and dye-

penetrant checked, if cracks are suspected, as some tube leaks have been experienced at these

welds.

Inspect the slope tubes for signs of erosion, corrosion or thermal stress. Problems in this area could

be caused by sliding ash and slag, chemical reaction of the ash and moisture, splashing or surging,

wave propagation, and flooding during filling. Some possible solutions are to maintain ash hopper

normal water level at least 30" below the tubes and have an overflow capable of handling excessive

amounts.


01/2016 of 70

Furnace Seal Inspection


01/2016 of 70

Lower Combustor – CFB Boiler

Maintenance Issues for the Lower Combustor / Hearth Zone are directly related to Unit Operation.

Improper SA Flow or drop in pressure can result in overheating of the Lower SA Ducts and Start Up Burners.

Improper PA Flow

o Low flow can cause the Fluid Bed to Slump and ash to enter PA Plenum.

o High flow can contribute to accelerated erosion of PA nozzles.

Start Up curve for refractory cure can reduce some refractory spalling repairs.

Cracks in the Plenum Corners above the header and at sidewall gusset supports due to unit expansion.

Inspection Focal Points

PA Nozzles –ash pluggage, broken, and erosion

PA Plenum –ash build up, gusset supports, corners

FBAC ACV Inlets –Grease Air Ports

SA Ducts –Overheat damage

Fuel Chutes –Ceramic Tiles

Start Up Burners –Erosion, overheating

Ash Return Vents –Gaps

SRD Duct Outlets –Refractory and Grease Air

FBHE Return Ducts –Refractory and FA Nozzles

Refractory –Spalling of ledges

Water Walls for erosion and condition of AMSTAR Spray

Lower Dead Air Space

Inspection includes the examination of all skin casing, insulation, refractory, seal boxes, tube

assemblies, and the structural condition of all expansion and support members, supports, braces,

and hanger rods.

Examine all support structures for broken welds, disconnected, broken, or bent rods and missing

nuts and bolts.

Check for bent or twisted supports.

Check all slope tube support buckstays.

Check all framing supports.

Examine condition of bottom slope tubes.


01/2016 of 70

Dead Air Space Support Steel and Hangers

Hanger Disengaged from Support

Visually inspect the dead air space for ash accumulations due to gaps at the slope tube membranes.

Also check sidewall casing structure for any indication of defects or cracks.

Damaged Waterwall Slope Tube

Large clinker or ash accumulations can build up in the tube assemblies in the top of the furnace and

eventually fall, damaging the lower slope tubes and the structural steel inside the lower dead air

space, especially near the side wall corners.


01/2016 of 70

Visually inspect the bifurcated tube membranes for cracking near the membrane end at the bottom

of the side wall tubes above the bifurcate. Dye-penetrant checking of this area is also recommended

if there is any history of tube failures. If tube failures have occurred or cracking is evident, treat the

membrane as follows:

Contour the ends of the membrane welds, creating a smooth radius. Cut the middle of the

membrane back from the end a few inches and drill a hole at the end of the cut. Use a pencil grinder

to remove any rough edges from the cut and hole.

Examine sidewall seal boxes for cracks, tears, and signs of expansion problems.

Side Waterwall Seal Box Crack

Furnace pressure or expansion can cause the slope wall scallop bars to tear adjacent to the sidewall

scallop bars. The tear can extend into the side wall tube, causing a failure.

Inspect seal plate condition where waterwall downcomers penetrate lagging. Check expansion

joints (boots) at the lower strut penetrations.

Furnace Waterwalls

Lower Sidewall Tubes


01/2016 of 70

Inspect the lower sidewalls, looking for signs of erosion caused by sliding ash. Also examine the area

around the lower sootblower openings for erosion.

On many units, the lower sidewall tubes at the center point are tied together by a solid plate.

Failures have occurred in this area, along the tube membrane, due to fatigue resulting from

concentrated areas of thermal stress or corrosion attack, at the high stress concentrations. Inspect

this area, looking for signs of fatigue or corrosion. If damage is found, replace the first two or three

tubes to either side of the centerline and implement the lower sidewall modification.

Furnace Bottom Slope Tubes

Inspect waterwall tubes in the coutant bottom for gouges, dents, bowing, and overall damage due to

slag falls, slag erosion, or a combination of the two.

Erosion (abrasion wear) from tumbling and sliding slag or flyash can wear down the tube surface

exposed to the furnace area. When this happens, the tube can fail from excessive thinning or from a

minor slag fall rupturing a weakened tube wall.

Large sections of slag from the upper furnace can dent the tubes and rupture them at the impact

area or cause an overheating failure elsewhere due to restricted flow.

Failure can occur in the dead air space side of the tubes, at the steel support lugs. The great force of

slag falls can deflect the hopper slope tubes along with the support steel.

Inspect for leaks in the sealed membrane. Leaks can result in overheating of the structural support

steel in the dead air space.

GUIDELINE

When evaluating gouges and dents in slope tubing, indentations that reduce the wall thickness

below the original Minimum Wall Thickness (MWT) should be considered for repair.

Tubing should be considered for replacement when wear or corrosion has reduced wall thickness

below original MWT.

Individual tubes or tubing panels should be considered for repair or replacement when warpage or

bowing has deflected the tube(s) more than 1 tube diameter out of line.

Waterwalls

Thoroughly inspect all waterwalls. Give particular attention to the following

Waterwalls around sootblower openings

Waterwalls around the windbox openings

Waterwall corners

Waterwalls in the high heat absorbing areas


01/2016 of 70

The extended side walls

Examine waterwalls around sootblower openings for erosion and wear.

Inspect the tubes adjacent to the blowers frequently to determine tube wall thickness. Ultrasonic

testing equipment and actual measurements can be helpful in determining any tube wastage.

If erosion is noted, check the alignment of the blower. The centerline of the swivel tube should be

perpendicular to the face of the boiler tubes. Check the distance of the centerline of the cleaning

nozzle to the face of the boiler tubes.

Inspect the waterwall tube membrane at the sootblower opening. In some instances, this

membrane can be relieved with a saw cut through the center.

Examine the waterwalls in the vicinity of the firing zone for corrosion and wastage. Thoroughly

check the walls around the windbox and corners.

Adjust coal fineness to prevent coarse coal from reaching the furnace.

Maintain equal distribution of coal to all fuel nozzles. Verify by clean airflow distribution testing of

the pulverizers and/or coal line mass flow tests.

Centerwall

On divided furnace units with centerwalls, observe and record the amount and direction of

centerwall tube panel bowing. While some panel bowing is acceptable, bowing in excess of several

feet out-of-plane may be indicative of operational or structural problems and should be investigated

further.

Deflection Arch

Rear waterwall tubes form the deflection arch, projecting forward at the top of the furnace rear wall

and then sloping back underneath the superheater and reheater vertical spaced assemblies.

Examine the upper arch for signs of erosion. Flyash/sootblower erosion can cause considerable

damage to the tubes and peg fins.

Closely inspect arch tubes adjacent to the furnace centerline for evidence of sootblower erosion.

Erosion is more prevalent in this area due to the droop of the lance as it is extended into the

furnace.

Check the entire arch. Depending on unit operation, erosion can occur either on the nose or 3 to 4"

above the bend. Eddying of flyash above the bend can result in even wear, problems may be

difficult to detect by visual observation.

Refractory under the tubes can be eroded away exposing the skin casing, resulting in skin casing

cracking and warping. On newer units the upper arch tubes will be of solid membrane design, which

in most cases has eliminated skin casing problems. Overheating of upper dead air space support

members can also result and can affect the structural integrity of this area.


01/2016 of 70

Examine the rear waterwall hanger tubes for erosion. The backs of the rear waterwall hanger tubes

are susceptible to flyash erosion where they penetrate the upper slope of the arch. To prevent

damage and subsequent ruptures, these tubes should be shielded at least 4 to 6" up from the arch

tubes and extend shields down to the seal box. In some instances, abnormal flue gas velocities

under the pendants will erode the front side of the tubes. To prevent damage these tubes should be

shielded at least 12" up from the upper arch tubes.

Check all penetrations through the arch for indication of seal damage. Check the steam-cooled

spacer tubes for erosion where they penetrate the upper arch.

Check for extended sidewall movement. Sidewall tubes can move away from the wall by as much as

1 to 1.5" allowing flyash to work its way down and bow the casing.

Check clearances between the reheater vertical spaced assemblies and the deflection arch


01/2016 of 70

Nose Arch Inspection Points


01/2016 of 70

Location of Wear


01/2016 of 70

Superheater Assemblies

The superheater inspection includes the external examination of all tube assemblies. It also includes

the examination of all fluid, steam, and mechanical spacers, tube shields, pad welds, flexible spacers,

and band type spacers.

To inspect the superheater, erect scaffolding or sufficient sky-climbers must be provided to

effectively conduct a thorough examination of all superheater assemblies and support members.

Inspect all vertical superheater assemblies for signs of hard ash deposits. If the deposits are

significant, recommend removal at this time.

Examine each group of assemblies separately, since each group is affected differently by gas flow.

Review previous inspection reports, then determine areas of concern.

Inspect tube assemblies for any sign of failures in the area of dissimilar metal welds. Variables that

can promote this failure are the following:

High temperature

Time in service

Differential expansion

External loading

Cycling of unit

Inspect all tube assemblies for any signs of warping, bulging, and swelling, which might be

indications of overheating.

CRITERIA: If tubes are swelled 2% over specified OD, a sample should be taken for analysis.

When measuring tubes, take measurements at least 18 inches from the shop welds or bends. This

eliminates the effects of manufacturing processes on the tube dimensions.

If problems have occurred in the past, recommend removing a tube sample section and send it to

the laboratory for analysis.

Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the

results to compare to measurements in future outages.

Superheater Division Panels

Steam-cooled spacer tubes help maintain the alignment of the division panels and minimize panel

sway. These spacer tubes bifurcate at the front of the furnace and proceed horizontally across the

left and right sides of the division panels. Because of this, wear between spacer tubes and the

superheater division panels can be a problem and can cause considerable damage if overlooked

during an outage.


01/2016 of 70

During the inspection, examine all elements and assemblies for any indication of bowing or signs of

misalignment. Examine horizontal tubes for misalignment. Broken slip spacers allow horizontal

tubes of the division panels to distort and collect slag. Once out of alignment, the weight of

additional slag could cause the tubes to sag. Realign any tubes out of alignment and add additional

flexible tube ties. Repair any broken flexible tube ties. Consider recommending replacement of any

misaligned tubes, which are badly bent.

Examine misalignment between flexible tube ties. In these areas, tubes can bow out of alignment

mainly due to the differential expansion between the panels. Check for misalignment between the

top and middle level of slip spacers. Check for misalignment between the roof tube and the first

flexible tie. Realign any bent tubes and add additional tube ties.

Examine girdling tubes for misalignment. Tubes bow out of alignment due to tie lugs breaking away

at the weld. This can be caused by the vertical differential expansion between the girdling tubes on

each side of the panel. Check for broken lugs on each side of the panel. Check for broken

connecting straps. Check for wear between the vertical girdling tube and the horizontal tubes of the

division panel. Install new tie lugs that allow for vertical expansion between the vertical girdling

tubes on each side of the panel.

Examine all elements and assemblies for wear. Tube wear between a steam-cooled spacer and the

division panel tubes can easily be seen when the tubes are separated using a pry bar. Mark each

worn tube so they can easily be identified when repairs are made. Inspect for tube wear between

each support lug and the bottom of the steam-cooled spacer. Inspect the steam-cooled spacer

tubes where they cross over between panels. Check for wear between the wrapper of a division

panel and the spacer tube.

Before any repair work is begun, make note of material changes. This information can be found on a

unit material diagram.

Superheater Division Panel Anchors

The front wall anchors for the spacer tubes on radiant reheat units are subjected to severe wear due

to furnace pulsations (Figure 28). In general, the superheater division panels move from side to side

while the front wall moves from front to rear. The radiant reheat inlet header acts like a buckstay to

reduce front wall movement. There is still some movement however, because the front anchors are

located between the radiant reheat inlet header and the top of the furnace.


01/2016 of 70

Superheater Division Panel Anchors

Thoroughly inspect the division panel anchors and check the spacer tube roller sleeves. They should

be free to rotate, and centered with respect to the offset tube sleeves. There should be a total of

3/8" clearance between the offset sleeves and spacer tube sleeves. Check to see if the collar is

rubbing against the offset tube instead of the spacer tube sleeve. Check for correct clearances so as

not to cause excessive collar-to-sleeve wear. Check for wear on the spacer tube roller shields.

In making recommendations for repair, make note to rotate roller shields so that the non-worn

surface would be facing the anchor tube shields.

Superheater Platen Assemblies

During inspection, examine the fluid-cooled spacer for tube wear. Inspect for wear between the

fluid-cooled spacer and the superheater pendant platen tubes on both sides .

Check for steam-cooled spacer tube wear. At the front of these assemblies, a steam-cooled spacer

tube passes between the first and second tube assemblies. The newer steam-cooled spacer lug

consists of a scalloped lug, a spacer lug, and a support lug located between two flexible tube ties.

Inspect possible wear areas. Inspect support lugs for thinning due to wear or oxidation. Inspect for

spacer lugs that may have come out of the support lugs.


01/2016 of 70

Replace spacer and support lugs if required. Type 309 stainless spacer and support lugs should be

used for increased alignment and durability. An arrangement utilizing spacer and support lugs on

both the top and bottom sides of the steam-cooled spacer tube provides the maximum amount of

alignment security.

Examine the assemblies for misalignment due to broken flexible tube ties. Realign any bent tubes by

placing channel pieces with nuts and bolts on both sides of the assembly to draw the tubes back in

place. Replace any broken flexible tube ties and add additional ties as needed. It may be helpful to

add a vertical girdling tube similar to those on the superheater division panels to maintain tube

alignment at the bottom of the assembly.

Examine any misaligned tubes between the flexible tube ties. Misalignment here is most likely due

to the differential expansion between dissimilar materials. Expansion problems in this area should

be discussed with the manufacturer before taking corrective action. Misaligned tubes in this area

are very susceptible to sootblower erosion. Recommend that tubes are realigned and additional

flexible ties added, providing they have not been subjected to erosion to the extent they would

require tube repair or replacement. Inspect for broken slip spacer and saddle lugs on the lower

sections. This would allow tube misalignment and tube-to-tube wear.

The outside wrapper tubes on each assembly should be examined for sootblower erosion. Inspect

for erosion of the outside wrapper tube in the area of tube metal change. Inspect for missing tube

shields or tube shields that have slipped down.

If sootblower erosion is a problem in this area, examine the sootblowing system. Check for

condensate in the steam blowing system. If condensate is present, check the thermal drain system.

Excessive steam pressure can cause rapid erosion. Check that steam pressure and temperature

match setpoints. Check frequency of sootblower operation. High concentrations of flyash can also

increase the erosion process.

Superheater Pendant Spaced Assemblies

The superheater pendant spaced assemblies are located directly above the furnace arch. This area is

susceptible to deposit buildup, wastage due to the combined effect of gas flows and high flyash

concentrations, and tube misalignment.

During the inspection, thoroughly examine this area for deposit buildup, abnormal wear or wastage,

tube misalignment, slip spacer condition, and support lug condition.

Inspect the front and rear steam-cooled spacer tubes at the points where they contact the assembly

tube elements.

Inspect for missing tube shields. Recommend repair or replacement of broken strap welds.

Conduct a wastage survey to assess wall thickness in the leading edges of every 10 assemblies above

the long retractable sootblowers and at the rear of the assemblies.


01/2016 of 70

Examine all flexible tube ties in this area for indications of cracking and broken welds. Flexible ties

can come out of alignment due to a restriction in movement, which could be caused by ash

accumulation under and between assemblies.

Low Temperature Horizontal Superheater Assemblies

The low temperature superheater assemblies can be either vertically hung pendant assemblies or

banks of horizontal assemblies, depending on boiler design, and are located in the backpass of the

boiler above the economizer. The horizontal assemblies are very susceptible to uneven

temperatures due to the cooler economizer outlet terminal tubes (horizontal superheater support

tubes) passing through the support saddles and causing the adjacent superheater metal surfaces to

be subcooled, relative to the rest of the tube surfaces.

During the inspection of the horizontal superheater, inspect for superheater tube pairs bowing away

from each other due to the uneven temperatures. If the tubes are not breaking away from the

saddle support, leave them alone until the next inspection. Check for flyash erosion on the front

return bends of the horizontal superheater, especially if the front bends extend above the backpass

floor. If this is a problem, recommend installing a method to shield the bends with stainless steel, or

install baffles to redistribute the gas flow adjacent to the tube bends. Whether a refractory or metal

plate baffle is installed, it should be installed so that the baffle is horizontal and does not slope

downwards towards the superheater tubes. This slope will accelerate wear on the tubes as gas and

ash sweep downward off the baffle onto the tubes.

Check for flyash pluggage between the rows of the horizontal superheater tubes. Check for flyash

erosion and pluggage at the rear wall and horizontal superheater assemblies.

Reheater Assemblies

The reheater inspection includes the external inspection of all tube assemblies. It also includes the

examination of all tube shields, pad welds, and mechanical spacers (flexible and band-type).

To inspect the reheater, scaffolding must be erected so that a thorough and safe inspection of all

reheater assemblies and support members may be conducted.

Inspect all vertical spaced reheater assemblies for signs of hard ash deposits. If hard ash deposits

are significant, remove them at this time.

Examine each group of assemblies separately, since each group is affected differently by gas flow.

Review previous inspection reports to determine areas of concern.

Inspect tube assemblies for any signs of failures in the area of dissimilar metal welds. Variables that

can promote this failure are:

High temperature

Time in service

Differential expansion


01/2016 of 70

External loading

Cycling of unit

Inspect all tube assemblies for any signs of warping, bulging, or swelling, which might be indications

of overheating.

If problems have occurred in the past, remove a tube sample from a section and send it to the

laboratory for analysis.

Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the

results to compare with previous wastage measurements and what will be taken in future outages.

Radiant Reheat Front Wall and Side Walls

The radiant reheat front wall and side wall tubes are located in the upper portion of the furnace

waterwalls in the area surrounding the superheater division panels.

During inspection of this area, check for bowing of the front and sidewall tubes. Realign as

necessary. Check for tube swelling due to overheating. Replace tube sections as needed. Check for

tube erosion, especially at the lower bends where the tubes go through the wall. Pad weld if needed

and install tube shields.

Check for tube metal loss due to tube rubbing. If metal loss is found, recommend installing stainless

steel tube shields at the points of contact. The tube shields should not be seal welded.

Reheater Vertical Spaced Rear Assemblies

The reheater vertical spaced rear assemblies are located after the reheater vertical spaced front

assemblies at the top of the arch.

Install wear strips in crossover tubes where there is contact with the rear waterwall hanger tubes.

Check for broken, burned off, or disengaged slip spacers.

Reheater Vertical Spaced Front Assemblies

The reheater vertical spaced front assemblies are located after the superheater platen assemblies

and are suspended above the arch.

Check broken or missing slip spacers on the front and rear sides of these assemblies, and note

location. Inspect all tube assemblies for signs and magnitude of bowing. Note location and severity.

Measure wastage on the leading elements of the assemblies in the area of the long retractable

sootblowers and record wastage. Sootblowers normally erode only lead tubes in an assembly

(unless out of alignment), but erosion can occur on second, third, or fourth tubes, etc. Appendix D

includes samples tables that are used to collect this data.

Check for flyash erosion resulting from vertical surface pluggage. This erosion can occur as much as

five to six tubes deep in an assembly. One possible cause is high velocity gas erosion, due to the

channeling of gases in a vertical section. This can develop when a reheater vertical section


01/2016 of 70

experiences severe pluggage, possibly due to a change to high sodium coal or misalignment of

vertical tube assemblies. Sootblowers cut flow path channels through the pluggage, which

eventually grow smaller and deeper into the bank. The resulting orifice creates high velocity uneven

gas flow distribution that is directed at the inner vertical tubes.

Flyash erosion on vertical tubes, resulting from plugged conditions typically exhibit areas of cratered

and protruding surfaces quite different from the classical, generally smooth flyash erosion patterns

found on screen tubes and rear pass horizontal surfaces.

If pluggage occurs during operation, determine the degree of it through the use of observation doors

or by an increase in gas side pressure drops, and in some cases by changes in individual tube

element steam temperatures.

During an inspection, examine closely the vertical sections known to be susceptible to plugging.

Failures due to high velocity gas channeling should be reported as flyash erosion and a description of

the pluggage and the circumstances should be carefully documented.

Check reheater vertical spaced front assemblies and furnace deflection arch for clearances (Figure

30). Inspect condition of tube shields and note locations of missing tube shields. Appendix D

includes samples tables that are used to collect this data.

Check condition of high crown seals where tubes penetrate the roof.

Rear Waterwall Screen Tubes

The rear waterwall screen tubes are located behind the rear waterwall hanger tubes. As their name

implies, they are formed by the rear waterwall tubes forming the arch and bending upward toward

the roof.

On some units, a refractory kicker baffle has been installed at the base of the screen tubes to

redirect the gas flow entering the horizontal SH and economizer sections. Flyash erosion can also

occur on the screen tubes directly above the kicker baffle. If erosion is evident, remove the top 2” of

refractory kicker baffle. Recommend exposing any eroded areas and repairing screen tubes as

required.

Conduct a wastage survey to determine where tube shielding is required. Shield screen tubes with

at least 12” of 309 stainless steel, in such a way that the bottom of each shield rests on the

remaining refractory kicker baffle. Recommend replacing the upper portion of the refractory kicker

baffle so that the bottom of each shield is embedded in the refractory.

Further up on the screen tubes, examine welded-tie vibration restraints for evidence of cracking

(Figure 31). If cracks are found, recommend repairing the affected tubes. If frequent tube failures at

these restraints have been responsible for excessive downtime and/or damage to adjacent tubes, an

additional row of vibration restraints may be required above the welded restraints.


01/2016 of 70

Cracking of Welded Tie Restraints


01/2016 of 70

Rear Waterwall Hanger Tubes

The rear waterwall hanger tubes are located above the deflection arch between front and rear

sections of reheater vertical assemblies. The hanger tubes are furnace rear wall tubes, which pass

straight upward from the furnace rear wall through the deflection arch upward to the roof.

Inspect all existing tube shields and pad welds . Look for cracks in welds, which are an indication of

problems resulting from temperature differentials.

Inspect the hanger tubes for wastage, especially at the top where they intersect with the roof tubes

and at the bottom directly above the slope tubes. If erosion seems uniformly excessive at any point

across the hanger tubes, a wastage survey is recommended.

The backside of the hanger tubes is susceptible to flyash erosion directly above where they

penetrate the arch tubes. The hanger tubes should be shielded anywhere from 4 to 6" from the arch

tubes. The shield should extend down to the seal box. In some instances, flyash laden flue gas will

flow under the pendant assemblies at higher than normal velocity, eroding the front side of the

hanger tubes. The hanger tubes should be shielded up to at least 12" from the arch tubes.

Inspect steam-cooled spacer tubes where they pass between hanger tubes. Inspect for wear at

contact points with the steam-cooled spacer tubes. Pad weld and install wear strips as required.

Examine hanger tubes in proximity of sootblowers. If erosion is evident, shields may be installed,

extending 2 to 3" above and below the centerline of the sootblower locations.

Closely inspect all welded tie vibration restraints for weld cracking which may be caused by vibration

due to combustion gas velocity or stress caused by ash loading.

Upper Dead Air Space

The upper dead air space is located at the top of the furnace between the furnace arch and the

backpass. Inspection includes the examination of all skin casing, insulation, refractory, tubes, and

the structural condition of expansion and support members.

During unit operation, local temperatures inside the upper dead air space are approximately 800F.

If casing leaks develop allowing furnace gases to enter the dead air space, temperatures can

approach 1500F. Overheating of structural steel at these excessive temperatures can lead to

distortion, loss of structural integrity and possible failure.

Visually inspect all supports, braces, and hanger rods for structural integrity. Randomly perform a

"tuning" operation on the hanger rods to check structural soundness by tapping the rod with a metal

instrument.

Examine all support structures for broken welds, bent rods, and missing bolts and nuts. Inspect for

bowing due to extreme temperatures. Examine for cracks, oxidation, and deterioration. Determine

how severe the problem is and explore possible methods for reducing or eliminating excessive

damage.


01/2016 of 70

Examine all hanger rods and support structures for integrity. Broken, missing or loose clevis pins and

rods must be replaced and properly tensioned. Inspect rods for elongation due to high

temperatures. Examine all turnbuckles for cracked, missing, or weakened assemblies.

Visually inspect all casing structures for any indication of defects.

Check for loose waterwall hangers.

Inspect for loose floor hangers that extend from the backpass extended sidewalls. Inspect for bent

center row hangers. Inspect for loose horizontal buckstay bolts.

Examine seal boxes. Inspect for cracks, tears, and signs of expansion problems. Examine casing for

indication of warping due to overheating.

Inspect all support buckstays for indication of bulging, twisting, and cracks.

Examine the condition of the refractory around the peg finned bifurcated tube assemblies. Missing

and deteriorated refractory and insulation material can cause erosion, overheating problems, and

heavy flyash buildup in this area. Remember that support structures are designed for a predicted

load and stress.

Any amount of skin casing expansion that is greater than the tube expansion must be absorbed by

the expansion joint that runs from left to right. Recommend repairing. Details are in Appendix G

Reduce sootblowing frequency and pressure if frequent tube erosion or refractory and casing

damage is evident. Recommend installing shields on the furnace side between the tubes, on top of

peg fins. On newer units, the rear waterwall upper arch will have a solid membrane between the

tubes instead of peg fins, which in most cases has eliminated the skin casing problems.

Inspect for structural damage at the roof of the dead air space. Reheater front vertical spaced

assemblies are located above the tubes forming the roof of the dead air space. Structural steel

damage occurs when flyash builds up under these assemblies which expand downward. The tube

assemblies push on the ash, which in turn pushes on the roof tubes and structural steel under them.

This flyash restriction can cause roof tube and reheater damage in addition to the structural steel

damage. If necessary, recommend installing sootblowers in this area to minimize ash buildup.

Furnace Roof Tubes

From inside the furnace, conduct a visual inspection of furnace roof tubes. List discrepancies on a

diagram showing plan view of the superheater and reheater assemblies (Figure 33). Inspect

refractory condition, noting any missing refractory. Inspect for sagging roof tubes, paying particular

attention to sidewalls. Check for worn or burned peg fins and missing refractory at the

steam-cooled spacer penetrations.

Continue the inspection inside of the penthouse, especially where sagging roof tubes or missing

refractory are observed. Check for skin casing overheating, deformation, or cracks. Inspect for

cracks in the seals around the superheater and reheater pendant assembly tubes where they pass up

through the roof tubes.


01/2016 of 70

Economizer

The economizer is located behind the rear low temperature horizontal superheater in the lower

section of the boiler backpass. The economizer is a bare tube, arranged in-line unit.

Inspect each of the banks of the economizer for polishing, tube alignment, and pluggage (Figure 34).

If erosion is a problem, consider recommending the installation of tube shields.

Check front and rear return bends and bare tube surfaces for metal wastage. Ultrasonic testing of

tubes is recommended when heavy polishing or erosion is evident.

Inspect for polishing around sootblower openings.

Check clearance between tube bends and the backpass walls, and between headers and sidewalls.

Examine all economizer support tubes. Check for tube misalignment. Check for tube erosion due to

flyash and gas flow. Inspect material condition of tube shields. Check for wear resulting from

metal-to-metal contact between the vertical support tubes and horizontal economizer tubes.

Inspect all elements for possible pluggage problems and investigate material condition of elements

covered with ash.

Check for flyash/sootblower erosion of tube bundle support hangers.

Inspect for broken support straps. Install additional straps as required. Pull up any elements that

may have sagged due to broken straps. Check for gouging between hanger supports and tubes.

Examine all wire mesh and refractory baffles and the tube surface condition under the baffled area.

Inspect expanded metal screens for tears, holes or missing sections. Inspect refractory baffle

condition noting missing, eroded, or crumbling sections. Inspect for tube wastage where the

refractory ends. In some instances where the tube return bends may be coated with Super 3000,

inspect for deterioration of refractory especially after water washing this section.

Inspect for gaps behind baffles at sidewalls. Increased gas velocities can polish the side wall tubes.

If any gaps are found, recommend installing mesh and filling with Super 3000 refractory.


01/2016 of 70

Economizer Inspection


01/2016 of 70

Examine condition of refractory at sidewall tubes and recommend repair as necessary.

Examine all header assemblies for metal wastage due to erosion. Outside diameter measurements

will indicate wear patterns. Inspect welds around tube nipples and headers for cracks. Install

erosion shields if necessary.

Examine the economizer ash hopper for structural defects. Inspect support steel and hopper

ductwork for signs of overheating and erosion to the refractory layer. Examine hopper for buckling

and cracks due to expansion problems. High temperatures at the hoppers can usually be traced back

to high temperature gases bypassing the economizer assemblies.

Inspect circumferential welds on the economizer inlet header. Check for stress corrosion fatigue

cracking at inlet tubes.

Penthouse

The penthouse is dead air space located on top of the unit. It houses all of the headers, which are

located in this area, along with the steam drum.

The amount of ash accumulations in the penthouse dictates whether or not removal is necessary

before, during, or after the inspection. If the ash is uniform in depth, it should be removed prior to

inspection. If repairs are required, remove the ash before or during the outage. If small individual

piles of ash are present, inspect the penthouse before ash is removed (individualized piles of ash

indicate areas of possible casing leaks). Exercise care while vacuuming; the ash will retain heat for a

longer period of time than that required for cooling the boiler.

Inspect the penthouse casing structure for any indications of problems. Cracking is the most likely

problem encountered.

Check for cracks in the casing panels that may occur at the transition points, at the junction of tube

assemblies, or at the high crown seals. Recommend repairing large cracks by grinding out the crack

and welding a casing patch in place. Repair small cracks by welding.

Inspect the floor area for cracked or missing refractory. Recommend repairing missing refractory by

patching.

Inspect all supports, braces, and hanger rods for structural integrity. Check all supports for broken

welds, cracks, bent rods, missing nuts or bolts, and for any bowing or any other signs of

misalignment. Check hanger rods for proper tension. Also check for missing or loose clevis pins and

the condition of the hanger rod turnbuckles.

Inspect all pipe braces, supports, saddles, and hangers.

Visually examine all headers located in the penthouse. Selectively check header tube root nipples. If

any problems are found or suspected, check all nipples on that header. Magnetic particle method

would work very well in finding cracks.


01/2016 of 70

Check the condition of the insulation material on all high temperature headers in this area. Look for

deteriorated or missing insulation along the walls and roof.

Check the condition of all expansion joints in the penthouse area. Look for signs of expansion

problems.

Thermocouples might be installed on some headers or tubes in the penthouse. Check the condition

of these thermocouples and associated wiring. Exercise caution so as not to damage any of these

thermocouples.

Observation Ports and Access Doors

Inspect observation ports and note condition of spring grips, latch pins, gaskets, liners, and door

opening refractory. Inspect the refractory material around openings in the observation door.

Inspect for slag buildup that can obstruct the view from an observation port. In areas where tube

assemblies are protected by refractory, check for any indications of problems.

Examine refractory material for cracks, erosion, and missing sections. Inspect access doors and note

condition of refractory around opening.

Example of Observation Port Inspection

Desuperheater

The purpose of the desuperheater is to control steam temperature through the use of cool

tempering water. Desuperheaters are installed in both the superheater and reheater circuits.


01/2016 of 70

The typical in-line desuperheater consists of a shell, liner, and spray nozzle assembly. The shell acts

as housing. The spray nozzle assembly introduces the tempering water. The liner protects the shell

from thermal shock when the relatively cold tempering water is injected into the steam system.

Conduct superheater desuperheater liner inspections every three years. This inspection is

accomplished by inserting a boroscope through one of the penetrating screw holes. Examine the

liner for any gross deformations. Examine the spray nozzles for any enlargement of the nozzle holes.

If extensive wastage is found, replace the spray nozzle. Examine the hole in the liner where the

penetrating positioning screw has been removed and measure the hole for elongation. Without

wear, the hole should be 1.06", +0.016", - 0.00" in diameter. Record any elongation and the

direction with relation to the run of pipe. If the hole has elongated 1/2" longitudinally or is within

1/4" of the edge of the reinforcing ring, recommend replacing the liner.

If inspection shows the liner to be in good condition, replace the penetrating screw through the

liner, and seal weld the screw to the pipe.

The reheater desuperheater liners are not subjected to the temperature differentials seen in the

superheater desuperheater and therefore do not usually require inspections as often.

Steam Cooled Enclosure (Backpass)

The backpass wall and roof sections are formed by the backpass side wall tubes at front, backpass

side wall tubes at rear, backpass front wall tubes, backpass front wall screen tubes, backpass roof

tubes, backpass rear wall tubes and the backpass lower rear wall tubes of the vertical gas pass. The

superheater tubes going to the backpass area from the "back pass at roof inlet header" form the

furnace front roof tubes (above the furnace) and furnace rear roof tubes (above the arch).

The most common problem found is erosion. Both sootblower and flyash erosion are often found

on the backpass wall tubes (Figure 38).

Sootblower erosion is commonly found along the paths of the sootblower lance.

The tubes on the front steam-cooled wall seem to have this problem most often.

Flyash erosion is commonly noted along the sidewalls and at the base of the walls, especially on

tubes that are out of alignment.

The backpass wall tubes should be inspected for overheating. Typical signs include swelling,

discoloration, circumferential or longitudinal cracks, and other problems.

Also, inspect the backpass walls for bowing, conditions of damaged refractory and casing.


01/2016 of 70

Backpass Inspection


01/2016 of 70

INTERNAL INSPECTION – WINDBOXES

General Description – PC Boiler

The windbox area is not a pressure part, but is a significant part of the furnace inspection. Before

making the initial examination of the windbox assemblies, a review of the windbox arrangement

drawing should be made to determine the windbox concept, fuel and auxiliary air compartment

arrangement, warm-up fuel arrangement, intended method of support of components, furnace and

windbox expansion values, and expansion provisions.

The basic functions of all burners of fossil fuels are to provide the time, temperature and turbulence

to unite the fuel with air and convert the potential chemical energy of the fuel to a more usable

form, heat energy. In order to accomplish the process safely and efficiently, manufacturers have

devised many arrangements of ignition, atomization and fuel-air mixing. In spite of state of the art

improvements to make burners safer and more efficient and extensive standardization, each burner

on a given steam generator seems to perform differently from supposedly identical installations on

other steam generators. We consider fuel burning a combination of science and art.

Tangential firing differs in concept from the wall burners in that the furnace itself is the burner. The

corner mounted nozzles serve only to inject fuel and air into the furnace in layers and at firing angles

that will promote mixing and burning in the furnace.

Oil burning is most efficient with wide open fuel air dampers and a high windbox-to-furnace

differential pressure. This is accomplished by throttling the auxiliary air dampers. Gas and coal are

efficiently burned with throttled or modulated fuel air dampers and lower windbox to-furnace

differential pressures.

Design Features

The following are general design information for tangential firing from furnace corners on field-

erected and modular units:

Fuel suitability - natural gas, waste gases, fuel oils (coal is not covered in this guidebook)

Design turndown ratio - 10 to 1, depending on fuel capability

Oil atomization capabilities - steam or air, wide-range mechanical, straight mechanical

Primary air used for coal transport only

Secondary air (all fuels) splits into fuel air and auxiliary air. Air enters furnace in tangential

layers and can be distributed behind the fuel or parallel to the fuel stream as necessary. The fuel air

dampers are positioned as a function of elevation loading. The auxiliary air dampers control

windbox-to-furnace delta-P.


01/2016 of 70

Minimum excess air

15 percent on oil*

10 percent on natural gas*

*For improved efficiency and lower emissions, special firing equipment is available, but must be

used in combination with sophisticated controls and careful load regulation.

In recent years environmental regulations have generated a need to burn fuel oils at very low excess

air. In many cases this has required changes to diffusers, air nozzles and oil gun tips. Each case must

be approached separately, but tangential firing has the capability of being operated at less than 3

percent excess air, providing plant instrumentation is suitable to control the process, and operators

and maintenance personnel are trained and motivated to follow more stringent practices than for

higher excess air firing. Low excess air firing requires:

1. Accurate, low maintenance, high reliability excess oxygen monitoring equipment.

2. Controls must be kept tuned and in automatic operation.

3. Secondary air dampers must be carefully set to be at equal positions at the same elevation at all

four corners. Depending on individual firing conditions, the upper or lower auxiliary damper may

have to be pinned or biased open to clear up smoky furnaces.

4. Fuel flows at each corner must be as equal as possible on an elevation basis. With oil firing this

means monitoring burner tip orifices for erosion and separating worn tips within wear groups on the

unit at any one time. The following is suggested standard for tip wear:

Effective Flow

Classification Increase, Percent*

New 0 to 3

A 3 to 5

B 5 to 7

C 7 to 10

*Effective flow increase is approximately equal to the percent increase of the orifice tip diameter

squared.

Discard all tips worn greater than 10 percent flow increase.

Windbox Arrangement – PC Boiler


01/2016 of 70

There is a vertical windbox assembly in each of the corners of the furnace. A typical windbox

assembly is divided into compartments for the admission of fuel and secondary air into the furnace

Coal compartments contain coal nozzles and also admit "fuel air" into the furnace. The term "fuel

air" is applied to that portion of secondary air that is supplied to a fuel compartment.

Auxiliary air compartments admit "auxiliary air" into the furnace. The term "auxiliary air" is applied

to that portion of secondary air that is supplied to the auxiliary air compartments.

Oil or gas compartments contain oil guns or gas nozzles for warm-up or load carrying duty. When oil

guns or gas nozzles are not in service, these compartments may function as auxiliary air

compartments.

The uppermost air compartments in some installations are termed the "overfire air" compartments.

The term "overfire air" is applied to that portion of secondary air that is supplied above the fire. This

air is used to control the formation of nitrogen oxides (NOx).

Located inside each air, coal, and oil compartment (>18” wide) are turning vanes, which direct the

air around the corner from the windbox damper section into the furnace.

The turning vanes impose a streamlined, even distribution of air to each air, coal, or oil nozzle.

Partition plates form the top and bottom of each compartment.


01/2016 of 70

Windbox Arrangement

Coal Compartment – PC Boiler


01/2016 of 70

Inside each coal compartment is a stationary nozzle and a tilting nozzle, which is also called a nozzle

tip or bucket.

The stationary nozzle is supported at one end by the windbox panels and at the other end by

support plates bolted to the sides of the nozzle.

The tilting coal nozzle tips pivot on pins attached to the stationary nozzle. The tilting coal nozzle tips

can be tilted upward and downward 25 from horizontal.

“Splitter plates” in the nozzle tip direct the flow of primary air and coal into the furnace as the nozzle

tip is tilted from horizontal. A seal plate pivots as required with the nozzle tip to close any gap that

forms between the nozzle tip and the stationary nozzle as the nozzle tip is tilted up or down.

One design of stationary coal nozzle for high-turndown applications is provided with an internal

horizontal splitter plate that separates the primary air/coal stream into a fuel rich and a fuel lean

stream. This ensures that the proper air/coal ratios required for combustion are available over a

greater unit load range. The nozzle tip itself contains diverging corrugated splitter plates and air

deflectors. The irregularly "v" shaped bluff body diffuser induces turbulence to the discharging

air/coal stream. In addition, it creates a low-pressure zone, which causes a high recirculation

pattern to form. These features promote a more stable ignition point over wide load ranges.

Oil Gun Compartment – PC Boiler

The corner windbox may also contain oil gun assemblies.

The oil guns, along with eddy plate side ignitors, may be used for warm-up of the boiler. The oil guns

may also be used for load carrying and to provide the ignition energy needed to light off pulverized

coal at adjacent elevations.

The oil may also be utilized to provide stabilization for the coal fires at low boiler loads.

Each oil gun compartment contains a tilting nozzle mounted on pins inside the windbox frame.

A tilt adjusting mechanism, similar to the design of the air and coal compartments, links the tilting

nozzle tip to the main tilt linkage.

The nozzle is fitted with a vane diffuser for directing the air around the oil gun tip in a circular

motion to create a recirculation zone for proper oil ignition.

Natural Gas Compartment – PC Boiler

Natural gas nozzles may also be provided as a warm-up or alternate main fuel source. They may be

installed in a compartment either alone or with an oil gun.

The natural gas burners consist of rigid piping supplying gas into wide flat nozzle assemblies located

directly behind the tilting windbox nozzle tips.

The gas nozzle tip is secured into brackets or guides on the sides of the windbox compartment.

Flame Scanners – PC Boiler


01/2016 of 70

Flame scanners are generally located in compartments between the main fuel elevations (coal or oil)

for monitoring fireball stability.

Filtered cooling air is delivered to the flame scanners through an air system consisting of the scanner

cooling air fans, filters, and dampers. Cooling air is supplied to each scanner assembly through the

scanner cooling air header located adjacent to the windbox.

Windbox Dampers – PC Boiler

Dampers at the inlet to each windbox compartment proportion the air depending on use, unit load,

and feeder speed.

One damper blade in each compartment is driven.

The damper blades in each compartment are connected by linkage so that they all move together.

Each damper should have a position indicating slot or bar on the end of the damper shaft, which is

visible from the outside of the windbox.

The slot or bar is parallel to the driven damper blade, and shows the exact position of the damper

blades.

Tilting Mechanism – PC Boiler

The fuel and air nozzles are positioned by either electric motor drives or pneumatic tilt drive

cylinders. Although there is one tilt drive for each windbox corner, the tilt drives are controlled so

that the nozzles at all corner windboxes are always at the same tilt angle.

Each corner elevation tilt indicator is equipped with a position indicator, a manual locking pin, a

shear pin, and a spring-loaded locking pin.

The fuel nozzles can typically tilt through a 50 range, 25 up and 25 down.

The oil nozzles can typically tilt through a 60range, 30 upward and 30 downward from the

horizontal.

The auxiliary air nozzles can typically tilt through a 60 range, 30 upward and 30 downward from

horizontal.

Low Nox Concentric Firing Systems (LNCFSTM) – PC Boiler

Tangential firing systems that have been modified for Low NOx operation may include the following

additional features

Modified coal nozzle tips (“Flame Attachment”) - a design to create zones of recirculation for ignition

stability nearer to the nozzle tip.


01/2016 of 70

Separated Over Fire Air (SOFA) registers - smaller windboxes located above the main windboxes to

provide a significant amount of the secondary air staging.

Fixed Offset “CFS” air nozzle tips - air nozzle tips constructed to direct a portion of the air into the

furnace along a line that is offset from the main fuel. When required, these are utilized only in the

main windboxes.

Horizontally (“Yaw”) adjustable air nozzle tips - air nozzle tips that are adjustable for the amount of

horizontal offset of the air introduction to the furnace. These may be utilized in the main windbox

and in the SOFA registers

These components are arranged in a fashion similar to traditional tangential firing equipment.

However, they incorporate the latest standards for durability.

The Low NOx Concentric Firing System (LNCFSTM) maximizes the NOx reduction capabilities of

existing tangential firing systems while minimizing unit modifications. An LNCFS uses a combination

of techniques to reduce NOx. These are "bulk furnace staging", “local combustion air staging”, and

"early controlled coal devolatilization."

Bulk furnace staging takes a portion of the combustion air, which is introduced at the fuel-burning

zone, and diverts it to retard air and fuel mixing. With conventional tangential firing, the

introduction of excess combustion air during the early stages of coal devolatilization contributes

significantly to the formation of NOx. The LNCFS maximizes the bulk staging concept by using both

separated overfire air and concentric firing.

Local combustion air staging is produced by introducing a portion of the secondary air, called

overfire air, above the primary firing zone. This is accomplished by utilizing a separated overfire air

(SOFA) windbox, which is installed above each corner windbox.

The concentric firing system utilizes a re-direction of the secondary (auxiliary) air, which is admitted

in the main firing zone, diverting it away from the coal stream. In this manner, combustion

stoichiometry is reduced by preventing the fuel stream from entraining with the air stream during

the initial stages of combustion. Fuel nitrogen conversion is reduced, while maintaining appropriate

oxidizing conditions along the furnace walls. The introduction of air in the concentric firing circle is

accomplished with installation of concentric (CFS) air nozzles.

Early controlled coal devolatilization utilizes the technique of early fuel ignition. Initiating the

combustion point at a close distance to the fuel nozzle produces a stable volatile flame that is more

easily controlled under sub-stoichiometric firing conditions. A specially designed coal nozzle is used

to promote a strong primary flame.


01/2016 of 70

LNCFS Firing System

An unmodified “standard” windbox arrangement is listed in the first column. As the table shows, the

differences in types of Low Nox windboxes are the choices and combinations of close coupled or

separated over fire air compartments. The selection of an LNCFS I, LNCFS II, LNCFS III or TFS 2000

windbox arrangement is based on the required reduction in NOx formation and the furnace

geometry which determines space available for these modifications.

LNCFS common terms and components – PC Boiler

LNCFS

A retrofit package designed to reduce NOx from pulverized coal units without replacing the existing

windbox structures. Generally speaking, LNCFS will utilize new auxiliary air nozzle tips (CFS), new

fuel nozzle tips, and one of three different methods of applying OFA. All the components of the

LNCFS are designed to withhold air temporarily and at different times during the history of coal

particle combustion within the furnace.

TFS 2000


01/2016 of 70

Coal firing system is designed for minimum total emissions. Techniques employed to reduce NOx

formation, such as sub-stoichiometric primary zone combustion, staging of fuel and air mixing,

reduced excess air, and lower heat release rates, are all aimed at controlling the combustion rate

and reducing peak flame temperatures. Since these conditions may increase the potential for CO,

hydrocarbons, and increased unburned carbon emissions, a balance among these opposing factors is

achieved through an integrated firing system that combines finer coal pulverization with advanced

fuel admission assemblies and in-furnace air staging utilizing multiple air injection levels.

P2 Coal Nozzles

The P2 coal nozzle tip assembly utilizes specific design features to guard against tip deterioration and

nozzle pluggage. The new tip is provided with a rounded corner design to decrease air turbulence in

the tip’s corners and reduce recirculation and deposition of coal and coke. It was developed

specifically for the demands of burner modifications for Phase 2 of the Clean Air Act of 1990.

Aerotip Flame Front Control Coal Nozzle Tips

Aerotip coal nozzle tips are a one-piece fabricated coal nozzle tip. They utilize design features to

guard against tip deterioration and nozzle pluggage. To minimize high temperature oxidation, these

coal nozzle tips utilize an erosion resistant material that offers a superb high temperature oxidation

resistance.

Nozzle tip shroud wall thickness is a minimum of 3/8" to resist warpage as well as erosion from the

coal stream. In addition, the interior walls of the tip as well as all leading edges of the nozzle tip

incorporate a weld overlay hardfacing material for increased erosion resistance.

To help prevent coal nozzle/tip pluggage, the stationary coal nozzle choke area is designed to

maintain proper coal stream discharge velocities based on fuel line velocities. In addition, the coal

nozzle tip utilizes internal splitter plates designed to better control fuel air, especially during tilted

conditions. By more effectively controlling fuel air, a more stable flame front position can be

maintained over the entire tip tilt range.

Crotch Cooling

Crotch cooling consists of an air deflector assembly at the extreme top and bottom of each windbox

to direct airflow adjacent to the refractory lined crotch areas of the bent waterwall tubes. This

improves the cooling of this area as well as controlling the buildup of slag in this area. Both of these

actions serve to increase the reliability and longevity of this refractory material. The windbox is

partitioned through the damper box to ensure continuous airflow through the crotch air deflectors

(no damper control of this airflow).

Air Restriction Blocks


01/2016 of 70

Air restriction blocks are used above and below coal nozzle tips to accommodate the reduced area

nozzle tips. Tip area sizing has been based the best airflow velocities for stable ignition low NOx

firing conditions.

CFS Tips

In the auxiliary air compartments, some special effects can be generated by the design of the air

nozzle tip. One specialized auxiliary air nozzle tip is called a CFS tip, which directs air away from the

adjacent fuel toward the waterwall. This simultaneously withholds auxiliary air from the adjacent

fuel and provides more O2 in the waterwall area that enhances slagging patterns.

CCOFA

Close-Coupled Overfire Air, is that part of the main windbox where the top air comes out. The

original arrangement had OFA, overfire air. After the top two coal elevations were positioned

(coupled) closer together, the larger top OFA compartment becomes known as the CCOFA.

SOFA

Separated Overfire Air refers to air registers that bias combustion air above and away from the main

burner zone. These air registers are physically separate from and above the main windbox.

External Burner Corner Examination – PC Boiler

The following items are general in scope and should be expanded by referring to contract specific

drawings or prior unit inspections.

Fuel Piping

Check piping at windbox for proper support.

Check oil piping at windbox for proper mounting and installation. Hoses must allow for cubical

expansion of windbox and for travel of retracting mechanism. Hoses must be mounted to operate

free of twist or bind, and shall be erected in accordance with standard hose arrangement drawings.

Check gas piping hoses at windbox. The mounting must allow for cubical expansion of unit, and

hoses must operate free of twist or bind.

Yaw Indicator

Check the actual position of each air nozzle tip and compare to the plant documentation for the

required position.

Check that the locking pin is securely in place.


01/2016 of 70

Yaw Indicator

Tilt Mechanism (external)

Inspect tilt linkage to insure components are in good condition and there is no interference with

other components, building steel, platforms, piping, etc.

Inspect indicator and pointer for proper relationship with tilting nozzles. Compare the indicator to

both local and remote position indicators of the driving unit or controller.

Inspect constant spring supports, if applicable, to insure proper functioning when tilts are actuated.

Insulation and Casing

Check appearance for any major defects or damage.

Make certain brackets for conduit or instrument tubing do not interfere with expansion movements

of floating casing.

Make certain all removable panels are bolted for tight seal against windbox pressure.


01/2016 of 70

Clearances

Clearance must be provided for removal of oil guns for cleaning.

Inspect coal piping at windbox to insure adequate clearance for removal of coal nozzles for

maintenance purposes. Where handrails are mandatory, removable sections may be utilized.

Damper bearings

During NOx retrofits new damper bearings may be installed in both the main windbox and SOFA

windboxes. The new style are graphite self aligning bearings. Refer to Figure 46. This damper

bearing shaft design can tolerate both dust and temperature, which in the past has caused

secondary air dampers to stick. Maintenance history has proven that minimal repair is required on

Graphite self-aligning bearings, however it is inevitable that even the Graphite material will

eventually wear out.

If it is found that the damper shaft has lateral movement to the point where the shaft sticks, and the

seal washer is opened and allowing dust to pack in and around the graphite bushing, replace the

bushing, spring seal and gasket. Tighten the four bolts firmly when rebuilding. Tighten the keyless

bushing (transverse torque component) to 125 ft/lbs to lock the lever arm firmly in place. Never pin

or lubricate any part of the keyless bushing. This will result in slipping between the shaft and lever.

Damper Shaft Graphite Bearing


01/2016 of 70

Internal Burner Corner Examination – PC Boiler

A proportional check should be made of each windbox and nozzle assembly internally.

Set tilts on"0" per indicator on drive mechanism outside the windbox.

All adjustable nozzle tips should be horizontal +0 degrees. If necessary, adjustment may be made at

the bellcrank.

Check clearances between the nozzle tips and the compartment plates. This clearance should be

3/8" minimum.

Check clearances between the side of the nozzle tips and the vertical channels or angles. This

clearance should also be 3/8" minimum.

Examine all linkages to insure that they are in good condition and that there is no interference with

other internal components.

Set tilts on +5o and recheck the horizontal clearance and then on -5o and recheck. Horizontal

clearances at this time should be 1/4" minimum.

Set tilts to +30o as indicated on the position indicator. Check actual tilt angle of nozzle tips. Indicated

versus actual should be within +1-1/2 degrees. Repeat at -30o. At extreme tilt positions, nozzle tips

shall not touch each other.

In oil compartments check location of diffuser cone. Refer to unit Instruction Manual for exact

dimensions.

Insert oil gun to firing position and clamp. Distance from face of diffuser cone back to the oil gun cap

should be as per unit Instruction Manual.

Examine ignitor horn and eddy plate assembly.

From inside the secondary air connecting duct, examine and operate dampers in each compartment.

Check for broken welds--blade to shaft. Inspect and correct any linkage that may have been

damaged in shipping and handling. Check installation of turning vanes, welding and completeness of

vanes.

Inspect joint between air connecting duct and windbox damper frame. This joint must be seal

welded inside the duct to preclude air and dust leakage into boiler room.

Make sure each compartment is clean and free of weld rods, scrap metal, tools, etc.

Windbox Nozzle Tip Field Adjustments – PC Boiler

NOTE: Adjustment and verification of the windbox nozzle tip tilt system should be carried out with

the windbox in the vertical position.

Set external direct drive tilt mechanism indicators at 0 degrees. per indicator scale.


01/2016 of 70

To verify the windbox is vertical and plumb, the reference marks on the windbox frame or the front

flange surface of the throat frame should be confirmed with a level.

Adjustable nozzle tips directly connected to the tilt drive mechanism by the horizontal reach-rod

should be in the horizontal position (relative to the windbox frame) within ± 2 degrees.

Use the measurement reference points clearly marked on both the windbox and the nozzle tip by

the fabricator for a level check.

Any necessary adjustments to the driving nozzle may be made at the threaded end of the reach-rod

(at the bell crank).

Adjustable nozzle tips in the air/oil/gas compartments which are interconnected with the driving

nozzle tip by means of vertical bars can be off from each other by as much as ±2degrees.

All adjustable nozzle tips should be properly centered within each compartment to provide at least

1/2" clearance between the tips and the windbox frame.

All coal nozzle assemblies should be properly centered within each coal compartment to provide

equal clearances between the coal nozzle tip and the adjacent partition plates. The min. clearance

should be 1/2". both of the coal nozzle assembly supports should be firmly resting on the partition

plate. If this condition is not met, excessive external loading by the fuel piping may be distorting the

arrangement of the assembly within the compartment.

Examine all linkages to ensure that they are in good condition and that there is no interference

between other internal components.

Inspect the clearances around the vertical nozzle tip connecting links and the internal connecting

bars, particularly where they pass through the slots in the partition plates. there should be no less

than 1/4" clearance around these items at any point throughout the ± 30 degree tilt range.

Tilts should be moved +5 degrees to -5 degrees and then back to 0 (zero) degrees. The clearance

between the partition plates and the nozzle tips should then be rechecked. the minimum clearance

should be 1/2".

Stroke the tilts between +30 degrees. and -30 degrees through component inspection, look and

listen for anything unusual that may indicate interference. Note that in the extreme positions of the

tilt range the actual tip position may be off from the indicated position by as much as ± 2 degrees.

Lubricating Windbox Internal Components – PC Boiler

Lubricant should be applied during field windbox overhauls. Link pins, stationary pins for bellcranks

(requires removal of bellcranks if it does not contain graphite sleeved bearings) and other accessible

pivots should be lubricated according to the unit instruction manual.


01/2016 of 70

Fluidized Bed Ash Cooler – CFB Boiler

Check the Function – Combustor bottom ash flows by an ash flow control valve to the FBAC and is

cooled by fluidization of the ash particles that creates a flow of ash between the tubes of each

pressure part assembly.

The bottom ash is cooled from 1700 degrees F to approximately 350 degrees F. The FBAC has two

sectioned compartments that are called the High Pressure and the Low-Pressure Compartments. The

water flow thru the high-pressure tubes is located between the boiler feed pump discharge and the

economizer. The water flow in the Low Pressure is cooling water. A vent or series of vents return

some ash flow back to the combustor transported by fluidization air. The vents allow filling of the

ash cooler with an inventory of ash so the DCS can perform a desired control scheme. FBAC Gravel

Screws remove top size bottom ash particles from the floor of the FBAC.

Instrumentation to the DCS for ash cooler operation includes lower bed ash temperatures, chamber

pressures for inventory indication, main vent temperature, waterside differential temperature and

final outlet ash temperature. Upgraded versions of the FBAC gravel screws include VFD or speed

control of the bottom ash screws from the control room to allow control of the FBAC chamber

pressures. Chamber pressure (ash inventory) to ash temperature relationship. Excessive fluidizing air

to pressure part erosion relationship. Sintering and DE fluidization conditions. Charge FBAC with

bottom ash prior to start up. Ash velocity range during operation is 2 –2.5 fps.

Inspection

Visual/UT inspections of all the HP and LP assemblies

Spread the assemblies apart to allow access for inspection.

UT worn thru Amstar Coating Areas.

Inspect the nozzles for erosion of casting-go no go gauges.

Rotate nozzles depending on erosion location or pattern.

Inspect refractory condition.

Copper Sulfate for Amstar Coated Tube Replacement

Inspect stainless cast handcuffs for cracking/replacement.

Handcuff bolt torque procedure. •Determine worn tubes to be shielded or replaced.


01/2016 of 70

CFB Cyclones – CFB Boiler

CFB Cyclones - Centrifugal path recycle cyclones are designed to remove about 99% of the solids

entrained by the gas.

Vortex Finder - in the top of the cone has a narrow laminar flow stream that allows only 1% of the

ash out the backend, but 100% of the gases of combustion do exit.

Key Components

Inlet Duct

o Ammonia Injection Grid (AIG)

o Expansion Joint

Outlet Duct

o AIG

o Expansion Joint

Cyclone Body

o Expansion Joints

o Grease Air Nozzles

o Vortex Finder

Inspection Items

AIG –Plugged nozzles, overheated lances

Refractory Walls –Missing sections of refractory

Expansion Joint –Slag buildup

Vortex Finder –Cracked welds/missing, misaligned assembly

Siphon Seal Pots – CFB Boiler

Function – Siphon Seal Pots - Allow the Cyclones to fluctuate in reserve level to store the surplus ash

during transitional periods. Heat transfer has three options for managing thermal inventory.

Return directly to the furnace and enrich the fluidized bed fire. Transits through SRDs(Solids

Return Ducts).

Momentarily fill the lower half of the cyclone as excessive flow is exiting the top of the

furnace.


01/2016 of 70

Pass through the FBHEs (Fluidized Bed Heat Exchangers) to reduce heat returned to the fire

in the bubbling bed. Flow is controlled by ACVs (Ash Control Valves).

Operating checks

Normal Operating Static Pressure range will increase to ~40” –80” wg. At 100” wg, operator

needs to watch closely for further increases in pressure. At 120” wg, there is possible

pluggage that will require action. Commissioning engineers must field test actual alarm set

points.

Low pressure suggest that fluidizing air flow is being lost.

High pressures (>100” wg.) suggest that the seal is plugging.

Fluidizing Air and Grease Air help to keep the ash flowing through the Siphon Seal Pots,

ACVs, and SRDs.

Key Inspection Points

Siphon Seal Pots

o Refractory

o Fluidized Air Nozzles

o ACV Plug Refractory Seat

o Grease Air Ports

o Seal Pot Support Beams (recently discovered during Spring 2012 Outage)

Ash Control Valves

o Plug condition

o Plug Shaft

o Bonnet

o Anti-Rotation Key

SRDs

o Expansion Joints: packing of ash can lead to fire in joint

o Refractory

o Grease Air Ports

SRD Outlet into Lower Combustor

Refractory Repairs


01/2016 of 70

Most Major Maintenance Issues for the Siphon Seal Pots/ ACVs/ SRDs are directly related to Unit

Operation.

Improper FA Flow or Grease Air Flow can result in plugging and pressure problems within the Seal

Pots.

Improper Ash Removal from the SRD Expansion Joints can lead to dangerous situations around the

Seal Pots and SRD Expansion Joints.

Start Up curve for refractory cure can reduce some refractory spalling repairs.

Properly trained and disciplined operators can prevent most maintenance issues on CFBs from

becoming major outage projects.

CFB Boiler Fluidized Bed Heat Exchanger

Inspection Focal Points

FA Nozzles

ash pluggage, broken, and erosion

Handcuff Castings -Bumper Pads

Refractory

Spalling around tube penetrations, jacking of inlet wall penetrations, and seams of floor,

sidewalls, roof, and inlet duct

PRE-OUTAGE WALKDOWN CHECKLIST


01/2016 of 70

This checklist is designed to prompt the inspector to methodically observe all components during an

inspection and to record abnormal data. The data will later be used to evaluate the unit’s condition.

Having a method to the madness of combing a unit from top to bottom adds value to the routine.

Flexibility to roam off course when necessary, knowing the checklist will get you back on track or

remind you which areas were missed.

Note taking is made simple when the item is already listed, all you have to do is circle a “problem

area” in the data-to-collect column and describe what you see.

The checklist coaches the inspector to look at areas that might otherwise be missed.

Sort the list so that the sequence is similar to the actual walkdown. Format the document as a

landscape page and make the “note” column larger. Highlight areas that are known “problem areas”

of the unit being inspected.

AREA & INSPECTION CRITERIA DATA TO COLLECT

Boiler Support

Boiler hanger rods Abnormal or loose hanger rods, integrity

Variable load and constant load spring hangers Bottomed-out spring hangers, loading

All vertical and horizontal buckstays Warpage or misalignment

All buckstay stirrups, bolts, nuts, and washers Integrity, abnormal condition

Expansion trams (boiler is hot) Readings at reference points

Safety Valves

Stem or packing Leakage

Drip pan Pluggage

Area between the safety valve and vent piping Binding or interference

Structural Steel

Structural steel for boiler or auxiliary equipment Interference

Grating and walkways Missing or loose sections

Handrails Missing or broken sections

Insulation and Lagging


01/2016 of 70

Insulated Areas Missing Insulation, discoloration, signs of

leakage

Duct insulation in areas of expansion joints Signs of buckling, leakage

Insulation in areas around inspection ports,

sootblowers, and access doors

Missing or damaged insulation

Poured refractory for damage Abnormal condition

Sootblowers and Furnace Probe

Local and remote operation by cycling each sootblower

through its operating sequence

Failure to operate

Sootblower supply lines, valves, and swivel tubes Steam leakage

Sootblower wall box Damage

Drive mechanism on all sootblowers Damage, interference

Cranks and tools to retract a sootblower which has

stopped in the "advanced" position

Available

Movement of air heater sootblower swivel mechanism Interference

Furnace temperature probe Damage

Ignitors

Operate each ignitor Lamp status, ignitor failure

Electrical cables, oil, gas, and air supply lines Damage, interference

Tilting Tangential Firing System

Fuel and Air Nozzles Degree of tilt

All overfire air nozzles Degree of tilt

All corners within 5° of each other Excess tilt

All coal piping entering the windbox (especially at

elbows or couplings)

Wear, damage, leakage

Fuel pipe hangers Damage, loose

All windbox air dampers Position per scribe mark on damper shaft

Compare All dampers on the same elevation Dampers not in same position


01/2016 of 70

Windbox and related duct work Leakage

Oil Guns

All oil and steam or air lines Leakage

All related piping and valves Leakage, damage

Oil gun advance and retract mechanism Failure to operate

Spare oil guns Dirty, not stored

Coal Piping

Coal pipes Indication of wear

Coal pipe couplings Sign of leakage

Coal pipe constant load spring hangers Expansion problems, loading

Coal Feeders - Gravimetric

Tension pulley Position

Feeder belt Tracking

Feeder housing (with stands 100 psig spike) Integrity, pressure damage

Observation windows and Doors Broken, will not close

Coal Feeders – C-E Volumetric

Drive clutch assembly Wear or damage

Hinged leveling gate lever Movement

Feeder housing. Integrity

Drive motor and gear reducer Noises, poor lubrication

Pulverizers

Mill foundation Cracks

Gear case oil Level, temperature, leakage

Examine the material being rejected from the mill (sign

of worn or improperly adjusted mill internals).

Excessive coal

Three journal assemblies Movement uniformity


01/2016 of 70

Separator body Coal Leakage

Classifier Do settings match

Mill motor, filters and foundation Wear, damage

Exhauster type mills: exhauster casing, foundation, and

bearing assembly

Wear, damage

Pulverizer gear housing and exhauster bearing housing Noise or vibration

Pressurized pulverizers: gear case and journal seal air

systems

Leakage or crimped lines

Air Preheaters

Upper/lower bearing assemblies. Wear or Damage

Oil Level, leakage

Air preheater seals Loud noise

Drive motor and gear reducer Signs of oil leakage

Air preheater sootblowers Failure to Operate

Boiler Water Circulating Pumps

Motor and related piping Leakage

Pump suction and discharge Log pressures

Motor cooling water Log temperatures

Compare data to normal operating conditions. Abnormal conditions

Fans/Air and Gas Ducts

Foundation bolts Crack or loose

Motor (use vibration meter) Excess vibration, log amps and bearing

temperature

Fan housings, air and gas ducts Damage, missing insulation, leaks,

expansion problems

Ash Removal Systems

All piping Leakage, pluggage

Fuel Handling Systems


01/2016 of 70

All coal handling systems Excessive spillage, accumulation

Oil and Gas piping Leakage

Pre-boiler Systems

All components and piping Leakage, missing insulation

BOILER INSPECTION FORM – CHECKLIST

LOWER FURNACE AREA

LOWER DEAD AIR SPACES

Membrane cracks – Especially membrane ends

Hanger rods

Hanger pins

Buckstay alignment

Buckstay connections to front/rear wall and side walls

Buckstay deformation

Seal boxes – leaks/cracks

Drain piping supports/welds

Enclosure support steel (gussets front/rear wall)

LOWER SPHERE/HEADERS/DRUMS

Door hinges

Door alignment

Door sealing surfaces

Orifice mounting hardware

Strainers/screens

Internal surface deposits

Backing rings

Drain piping connection


01/2016 of 70

BOTTOM ASH HOPPERS

Bottom sluice nozzles

Weir water headers

COUTANT UNDERSIDE OF SLOPE

Scallop bar cracks at seal plate

Drip screens

Drip screen support bar

Membrane cracks

Tube surface cracks

COUTANT TOP SIDE SLOPE

General deformation of tubes

Impact damage to individual tubes

Membrane cracks at junction of front/rear wall and side wall tubes

Membrane cracks top and bottom off set tubes at centerwall

Off set tubes around water cooled doors

Sliding ash erosion of side wall tubes at front/rear wall

Sliding ash erosion at upper bend of Coutant

Corrosion in centerwall seal box area

Wear bar (cracks, weld, wear)

MID FURNACE AREA

LOWER SOOTBLOWER ELEVATION (TYPICAL AT ALL ELEVATION)

Membrane cracks at off set tubes

Seal box refractory

Seal box wall sleeve

Tube erosion

Lance tubes cracks


01/2016 of 70

Lance tube nozzles

Lance tube alignment and depth and cleaning radius

Corner tube erosion

Lance tube rub damage

BURNER ZONE

Clean upper/lower crotch area

Membrane cracking at upper/lower crotch

Eroded/corroded tubes at upper/lower crotch

Membrane cracks in ignitor off set tubes

Overheating in ignitor off set tubes

Ignitor components

Fly ash erosion of wall tubes in coal nozzle tip area

Burner tip alignment

Burner tip linkage

Burner tip condition – Overheating, erosion, broken welds, warpage, etc.

Coal Nozzle – Erosion of nozzle, burner gate, inlet elbow

Auxiliary air tip alignment

Auxiliary tip linkage

Auxiliary air tip condition

Flame scanner guide tube

SOFA tips

SOFA tilt linkage

SOFA alignment

SOFA support frame work

CENTERWALL

Panel to panel rub


01/2016 of 70

Fatigue/corrosion in seal box

Hanger springs

Panel alignment/distortion

Sliding ash erosion – penetrate at front/rear wall

Sliding ash erosion at lower bends

Membrane cracks

Rub damage at upper rear wall arch penetration

WATERWALLS

Clean selected areas based on history and characteristics of unit design

Corrosion

Erosion

Discoloration

Swelling/blisters

Deformation

Membrane conditions

Tube surface condition – cracks/pock marks etc

Rear wall outlet header tube nipples (cracks at nipple to header and field welds)

UPPER FURNACE AREA

RADIANT WALLS

Stitch welds

Alignment

Tie welds

Clean tube surface for evaluation

DRUMS

Feed pipe, Continuous blowpipe, & Chemical feed pipe including support brackets and “U” bolts

Downcomer perforated screen box


01/2016 of 70

Primary separators including secondary separators and attachment bolts

Internal shroud and separator baffles

Corrugated Plate Dryer box and attachment bolts

Drain (drip) pipes

Door hinges and hardware

Door alignment

Door sealing surfaces

Debris

UPPER FURNACE ARCH

Sootblower erosion

Slag erosion

Off set tube membranes at screen/hanger tube openings

Rear wall outlet header tube nipples

Membrane/peg fin cracks

Coatings

Refractory

SCREEN TUBES/HANGER TUBES

Fly ash erosion on leading side at arch

Sootblower erosion

Corrosion in seal box areas

Loose tubes

ROOF TUBES

Sagging roof tubes

Peg fins/ Refractory

Rubs from adjacent assemblies

UPPER DEAD AIR SPACE ENCLOSURE


01/2016 of 70

Hanger rods

Structural steel

Seal boxes (sidewalls, hanger tubes, headers)

Membrane cracks (below rear outlet header, extended side wall)

Drain line connections

Buckstay connections to rear wall

RETRACT SOOTBLOWER OPENINGS/TEMPERATURE PROBE

Membrane cracks at off set tubes

Seal box wall sleeve

Tube erosion

Lance tube cracks

Lance tube nozzle

Lance tube alignment

Lance tube rub damage

Seal box cracking/leaks/deterioration/seal box refractory

Inserted alignment

CONVECTION PASS AREA

EXTENDED SIDE WALLS AND BACKPASS WALLS

Mechanical rubs from horizontal surface (economizer/SH/RH)

Fly ash erosion (screen tubes and hanger tubes)

Erosion at any gas deflection baffle (sootblower/fly ash)

Membrane conditions – solid or peg fin

Off set tubes at boiler access doors (Fly ash erosion, peg fin cracks, etc.)

Refractory at boiler access door off set tubes

Mill board at access doors

GAS TOUCHED HEADERS


01/2016 of 70

Erosion (Fly ash/sootblower)

Nipple alignment

Nipple welds

Header Supports

Overheating/Swelling/Blisters Discoloration

OD measurements, shear wave, UT, MT, PT, replication

Internal inspection

Header Distortion

ECONOMIZER

Pluggage

Platenizing

Alignments

Sootblower erosion at hangers

Fly ash erosion (Fin tube, Hangers and alignment straps)

Connection between hanger tube and assembly tube

Hanger tubes/straps

Gas distribution baffle conditions

Erosion throughout the bundles (spread or lift bundle for inspection)

Cracking at fin ends

GAS OUTLET DUCT

Expansion joints

Structural steel trusses/struts

Overheated duct work

Fly ash erosion

Economizer hoppers (Pluggage cracks erosion)

HIGH TEMPERATURE SURFACE AREAS


01/2016 of 70

PENDANT SUPERHEATER & REHEATER SURFACES

Slag accumulation

Tube deformation within an assembly

Sootblower erosion

Fly ash erosion

Flex tie rubs

Fluid cooled spacer rubs

Mechanical rubs from other tubes or supports

Clean selected area for surface evaluation

Take wall thickness readings at selected sites

Take OD readings at selected locations on tube which operate in the creep range

Inspect tube for swelling, discoloration or blisters

Observe and record general alignment of assemblies

Shields

HORIZONTAL SUPERHEATER & REHEATER SURFACES

Hanger support system

Slag accumulation

Tube deformation within an assembly

Sootblower erosion

Fly ash erosion

Flex tie rubs

Mechanical rubs from other tubes or supports

Clean selected areas for surface evaluation

Take wall thickness readings at selected sites

Take OD readings at selected locations on tube which operate in the creep range

Inspect tube for swelling, discoloration or blisters


01/2016 of 70

Observe and record general alignment of assemblies

Shields

PENTHOUSE

HIGH TEMPERATURE HEADERS

Discoloration

Scale

NDE evaluation (OD,MT,PT,X-ray, shear wave, bore scope, replications)

Nipples (welds, discoloration, scale, OD, wall thickness, misalignment)

Supports (hanger rods, U-bolts, etc.)

High Crown seal

LOW TEMPERATURE HEADERS

Discoloration

Scale

Nipples (welds, discoloration, scale, OD, wall thickness, misalignment)


High Crown seal

CASING

Cracks

Overheating

HANGER RODS

Looseness

Missing clevis pin lock wires

Broken components

Special case – on divided furnace be sure centerwall rear hanger is not insulated with hot reheat

outlet headers

LINKS


01/2016 of 70

Discoloration

Scale


Vent piping connections

NDE evaluation (OD, MT, PT, X-ray, shear wave, bore scope, replications)

DESUPERHEATERS

Discoloration

Scale


NDE evaluation of alignment and positioning pins (MT, PT, X-ray, bore scope)

Spray Nozzle

boiler inspection guideline - neeps - nee …€¦ · · 2017-08-30boiler inspection guideline...

Documents