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Fusion Bonded Epoxy Operational Training Course

Copyright, Disclaimer and Waiver of Liability

This course includes many images and other elements designed to enhance your learningexperience. These elements are relatively easy to copy. However, each is protected under the

same copyright laws that apply to books, movies and other traditional media. Unauthorized

copying may result in substantial liability. You must read the following copyright notice and

disclaimer, and by viewing all or any part of this CD you accept full liability for any copyrightinfringement you may commit with regard to these materials and acknowledge that you understand

the National Association of Pipe Coating Applicators assumes no responsibility for the

interpretation or use of the course materials and that the course is not a safety or environmentalcourse.

Copyright 2003 by National Association of Pipe Coating Applicators (NAPCA).

The text, photos, graphics and all other elements comprising this course are copyrighted materials

owned by NAPCA, and NAPCA owns a copyright in the selection, coordination, and arrangementof the course as a collective work. Except as expressly permitted below or under U.S. copyright

law, you may not copy, reproduce, republish, distribute, translate, or transmit the course or any

course element in any form without the prior permission of NAPCA. Copyright violations may

result in criminal or civil liability. These materials are provided only for your personal use. Youmay print out one hard copy of any material provided on this CD. You may retain those printed

materials and use them only for your personal reference. All other uses are expressly prohibited.

This course is not and does not purport to be one dealing with safety and environmental issues and

does not set forth safety and environmental issues, regulations, laws and other safety and

environmental materials which may be pertinent to the course material. You understand you mustgo to other sources in order to ascertain such safety and environmental information. NAPCA

assumes no responsibility for the interpretation or use of these course materials or the application

of same, nor does it assume any responsibility whatsoever with regard to safety and environmental

issues which may be associated with the course materials.

Indemnification

You agree to indemnify, defend, and hold harmless the National Association of Pipe Coating

Applicators against any and all actions, claims, liabilities, damages, costs, and expenses including,but not limited to, reasonable attorneys fees, which in any manner may arise or be alleged to result

from your unauthorized copying, distribution or transmission of the accompanying coursematerials or any copyrighted element thereof or which in any manner may arise or be alleged to

result from any safety or environmental violation or other safety or environmental matter which

arises or may arise in any way from your exposure or application of any of the course materials.


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Credits and Acknowledgements

This is the first edition of the National Association of Pipe Coating Applicators FBE Operational

Training Course. On behalf of the Board of Trustees, we would like to thank Dick Brunst,

President, Western Pipe Coaters & Engineers, Inc., who chaired the committee, which developedthe course for his dedication. Without Dicks strong leadership, the course would never have cometo fruition. We also would like to thank Lee Evans, Vice President, ShawCor Pipe Protection

LLC, for chairing the Editing Committee, which finalized the course. Furthermore, ShawCor Pipe

Protection LLC provided the course CDs to NAPCA free of charge. Many other people fromnumerous Regular and Associate Members contributed to the development of the course. We

appreciate their hard work and thank them for their contributions. Below is a list of those

companies which participated. They were numerous, and we believe we have shown them all.However, if any company, which worked in making the course a reality, is not included in the list,

we apologize for the omission.

Regular Members

The Bayou Companies, L.L.C.

Commercial Coatings Services, Inc. (CCSI)

Dura-Bond Coating, Inc.

eb Pipe Coating, Inc.L.B. Foster Company

Midwestern Pipeline Services, Inc.

Mobile Pipe Wrappers & Coaters, Inc.Perma-Pipe, Inc.

ShawCor Pipe Protection LLC (formerly Bredero Price Company)Western Pipe Coaters & Engineers, Inc.

Associate Members

CRC Evans Pipeline International, Inc.

DuPont Powder Coatings/Nap-Gard Pipe CoatingsErvin Industries, Inc.

Hoffman Blast Room Equipment, Inc.

3M Company

National Metal Abrasives, Inc.The Valspar Corporation

USF Surface Preparation

Wheelabrator Abrasives, Inc.


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Introduction

Welcome to the Fusion Bonded Epoxy Coating Operational Training Course established by the

National Association of Pipe Coating Applicators ("NAPCA"), the trade association for the plantpipe coating industry. We are pleased you have made a commitment to enhance your skills and

knowledge to further your career. This Operational Training Course was developed as a service

to the pipeline industry to assure personnel involved in the operations of fusion bonded epoxycoating plants and all inspection personnel are fully qualified to perform their duties. The need

for fully qualified, well trained operating and inspection personnel has become a major issue forpipeline owners and operators.

Recently, the officers and trustees of NAPCA were asked to discuss current and future problems

in the plant-applied coating industry. It was the consensus of these officers and trustees that thereis a real need for training of pipe coating operating personnel and inspectors who do work at

coating plants. Many times the applicator has to train these people on what is required duringactual operation, which may cause problems where none exist. Training of all operatingpersonnel and inspectors would be a big step toward total quality control, thus benefiting both

applicators and end users. This training course is a beginning. It is important that you take the

next step in learning and applying the information and skills taught in this course in your dailywork. We value your comments, suggestions and ideas for improvement to this program. Please

feel free to write us, and we will discuss your thoughts. Our address is as follows:

National Association of Pipe Coating Applicators

Am South Bank Building

333 Texas Street, Suite 717Shreveport, Louisiana 71101-3673

Telephone (318) 227-2769Telefax (318) 222-0482

If you would like more information regarding NAPCA, please visit our website at

www.napca.com. Our website contains the history and an overview of our association, a

complete listing of all of our members throughout the world, all of our application and otherbulletins, and advertising provided by various members.

History

Fusion bonded epoxy (FBE) coating of below ground pipelines to provide corrosion protectionwas developed in 1959. Full commercial availability to the industry was achieved four years laterin 1963. It was one of the first truly effective film coatings. At first, its use was limited, and

operating companies were somewhat skeptical of its ability to eliminate external corrosion on the

pipeline. Today, FBE is one of the most popular coatings being used by the industry throughoutthe world. In 1996, over 83 million square feet of pipe were coated with FBE, representing morethan a third of all coatings applied.


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Throughout the years, FBE formulations, application methods, testing, and uses have changed,

bringing about a much improved product for use by the end user. This FBE training program is

another effort on the part of the industry to give pipeline companies the highest quality productpossible in the corrosion protection to their pipelines.

Chemistry of Fusion Bonded Epoxy CoatingsI. Components of FBE Coatings:

A. FBE coatings are formed from four constituents:

1. An epoxy resin which forms the coating basis.

2. A curing agent for initiation and completion of polymerization.

3. Filler materials and pigments for improving properties and adding color.

4. Additives, which act as flow controllers to improve viscosity when all

constituents are melted together.

B. Chemistry of Coating Formation:

1. Epoxy Resin + Curing Agent (amine)-----> FBE Coating

2. Properties (both chemical and physical) depend upon composition of the epoxyresin and the curing agent(s).

3. As temperature of the mixture is increased, the formed FBE powder melts andbecomes a viscous liquid. As the liquid FBE cools, it becomes a gel or semi-solid

and ultimately a solid coating. Cross-linking actually causes the material to

become solidified.

4. Formulation of FBE coating depends on many concerns:

a. Manufacturer:Will the coating react or cure before it is applied by theapplicator?

b. Applicator:Will the coating adhere and remain on the pipe afterapplication and for many years to come?

c. Contractor:Is the coated pipe tough enough to withstand rockimpingement, handling, and other mechanical shock?

d. End User:Will it stay on the pipe until the end of the design life of thepipeline? Can it be repaired easily?


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Mechanical Pipe Cleaning

An abrasive blast-cleaning machine cleans pipe. In the machine, abrasive is hurled against theexterior of the pipe by blast wheels rotating at high speeds. The high velocity abrasive knocks

dirt, scale and rust off of the surface of the pipe. A dust collector is used in conjunction with the

abrasive blast-cleaning machine to remove dust-laden air and filter it, and to cool the abrasive.

This chapter discusses the following topics:

Abrasive Blast Cleaning Machine

1. Wheel Unit

2. Cabinet

3. Elevator

4. Separator

5. Dust Collector

ABRASIVE BLAST CLEANING MACHINE

Figure 1.1 Abrasive blast cleaning machine.


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This equipment is used by most pipe coating applicators. There are various manufacturers of this

equipment. Machines come in different sizes and configurations with slight variations ofindividual components. This chapter will only describe the types of centrifugal blasting machines

used by the majority of pipe coating applicators.

The abrasive performs the actual work of cleaning and profiling by impacting the surface to be

cleaned. It is continuously recycled through the machine that consists of five major components

(Figure 1.1):

1. Wheel Unit

2. Cabinet

3. Elevator

4. Separator

5. Dust Collector

Additional machine components and features, which are essential in an efficient operation,

include:

Ammeters

Standard

Digital

Vestibule and seals

Sunburst type

Brush type

Sheet rubber

Combination brush and sheet

Control system packages

Relay logic

PLC logic

Abrasive level monitoring

Abrasive flow control systems

Manual/Mechanical

Automatic magnetic variable abrasive flow control

Wheel Drives and Speed Control

Unit bearing


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Direct drive

Speed control

Cabinet liner packages

Manganese

Cast chrome molly

WHEEL UNIT

The wheel unit is similar to a centrifugal pump. The abrasive flows through the center of the

wheel passing through an impeller that rotates at the same speed as the wheel. The impellerproportions the abrasive and aligns its release to each vane. (Figure 1.2).

Figure 1.2 Exploded view of a wheel unit.

The abrasive releases from the impeller through the opening in the control cage that is mountedat the center of the wheel but does not rotate. The setting of the control cage opening controls the

blast pattern location on the work surface (Figure 1.6). Rotating the opening will move the

location of the blast pattern on the work surface accordingly.


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Figure 1.3 Unit bearing type wheel assembly - belt driven design.

Figure 1.4 Direct driven wheel assembly.


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Figure 1.5 Bi-directional wheel assembly.

The distribution of shot striking the pipe in the blast pattern is not even. A "hot spot" is createdwhere the highest concentration of the abrasive hits the pipe at the most effective angle (Figure

1.6).

The "hot spot" is where the abrasive impacts the surface at approximately 90 degrees. The

distance from the wheel to the work surface determines the length of the "hot spot" area.Normally the distance from the vane to the pipe is 16-18 inches, (40-50 cm) and the "hot spot"length is 8-10 inches (20-25 cm). The area outside the "hot spot" receives less cleaning due toless concentration of abrasive and lower angle of impact.


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Figure 1.6 The setting of the control cage opening controls the blast pattern location on the

work surface.

Since the pipe is spirally conveyed through the cleaning machine, the lead (forward travel of thepipe for each revolution) should not exceed the length of the "hot spot" or a "barber-pole" effect

will result. The lead is a function of the pipe diameter and the conveyor wheel angle.

Most blast machines used in the pipe coating industry are the two (2) wheel up-blast design. (See

Figure 1.7). The spiral motion of the pipe passing through the blast pattern of the two (2) wheelmachine should allow between five (5) to seven (7) exposures to the propelled abrasive to assurebest cleaning results.

The main wheel components consist of a balanced set of blades, an impeller, and a control cage.

They wear out as a complete set of components. Most parts manufacturers offer replacement kits,

which consists of all three components (Figure 1.2): one (1) set of blades, one (1) impeller, andone (1) control cage which should be installed at the same time.

Wheel blades/vanes are balanced sets to within one (1) gram. It is most important that they are

always changed as a complete set to eliminate excessive wheel vibration and bearing wear.

Table 1.1 Approximate abrasive flow rates (19-1/2" dia. wheel with 2-1/2" wide vanes)

(lb/min)

R.P.M.H.P.

1500 1800 2250 2480 2660

10 570 350 210

15 880 540 340

20 1200 750 460 380

25 960 600 500


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30 1170 720 600 540

40 1580 980 810 720

50 1200 980 900

60 1470 1200 1100

75 1470 1370

ABRASIVE VELOCITY 160fps 195fps 245fps 270fps 285fps

Table 1.2 Approximate abrasive flow rates (21" dia. wheel with 5" wide vanes) (lb/min)

R.P.M.H.P.

1500 1800 2250 2480 2660

10

15 455 316 202

20 733 509 326 268

25 702 449 370 321

30 895 573 471 410

40 1280 819 674 586

50 1066 878 763

60 1313 1081 939

75 1683 1386 1204

100 2300 1893 1646

ABRASIVE VELOCITY 170fps 205fps 256fps 282fps 303fps

The wheel is the "heart" of the cleaning machine. Wheel maintenance is important. Worn blades,

impeller or control cage can alter the blast pattern and cleaning efficiency. Other components of

the machine are accessories that deliver abrasive to the wheel and remove spent abrasive anddust.

Table 1.3 Wheel maintenance check list.

WHEEL UNITS DAILY WEEKLY MONTHL

Y

1. Check wheel for vibration. X


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2. Check blades or vanes. X

3. With blades removed, close housing and runwheel.Check for vibration.

X

4. Inspect and replace impellers if badly worn. X

5. Inspect control cage. If bevel edge of the opening

has worn way, should be replaced.

X

6. Inspect wheel housing liners and deflectors,change as necessary

X

7. Check blast pattern for correct setting. X

*8. Record Ammeter reading. X

9. Check ammeter for accuracy with Tong ammeter. X

10. Check wheel belts. X

*Ammeter should be steady at full load (or determined setting). Violent fluctuations indicateimproper belt tension, bearing trouble, inadequate supply of abrasive, or drag in some moving

machine part.

RULES OF THUMB:

Excessive vibration at the wheel usually indicates wornout blades or wheel head.

If squeaking/squawking occurs while starting motor onwheel, it usually indicates loose belts.

The leading edge of the control cage opening isapproximately 180 from the leading edge of the blastpattern.

If grinding noises occur in the wheel during start-up, it

usually indicates misalignment of components whichshould be corrected.

When replacing worn blades, replace the complete set.The impeller and control cage should be replaced at thesame time.

Wheel blades are considered worn out when grooves orwear reaches the original thickness.


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CABINET

The blast machine cabinet contains the blast process and keeps the rebounding abrasive, dust,

rust, mill scale, etc. in a confined area where the abrasive can safely be reclaimed, cleaned and

recycled, and dust and other refuse removed. The cabinet consists of a steel box with vestibulesand seals located at each end through which the pipe passes. The cabinet is constructed in such amanner as to collect the spent abrasive in the bottom and direct it to the elevator boot for reclaim.

There are two basic cabinet designs.

UP BLAST DESIGN

On the up blast machine the blast wheels are mounted under the pipe. The wheels are always in a

fixed position in relation to the bottom surface of the pipe. The majority of this type of machine

reclaims the abrasive by gravity. This requires a sloped hopper to the elevator boot. This type ofmachine usually requires a pit.

Some up blast machines have an auger in the bottom of the cabinet to move abrasive to the

elevator boot. These machines may or may not require a pit.

Figure 1.7 Up-blast cleaning theory of operation.

DOWN BLAST DESIGN

The down blast design is configured with the wheels mounted above the pipe (Figure 1.8). Since

the top of pipe varies by pipe size (the bottom of the pipe is usually at a constant or near constant

height), the distance from the wheel to pipe varies. This makes the wheels less efficient whenblasting small diameters. It also allows the blast pattern to spread out. In extreme cases, the blastpattern becomes so long, it blasts into the cabinet seals.

In some down blast designs, the wheels can be moved up and down to keep the distance from the

wheel to the pipe constant.

Down blast machines can be pit-less or require a shallow pit. They may also be gravity or augerreclaim.


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Figure 1.8 Down-blast cleaning theory of operation.

Table 1.4 Cabinet maintenance check list.

Cabinet Maintenance Check List DAILY WEEKL

Y

MONTH

LY

The cabinet should be free of leaks. Flying abrasive

is dangerous to personnel and nearby equipment.Lost abrasive is expensive.

1. Inspect cabinet interior for evidence of abrasivewear

X

2. Clean loose abrasive from roof areas and return it

to system. Determine and eliminate the source ofloose abrasive.

X

3. Inspect wheel housings and liners. Replace asnecessary.

X

4. Check entrances, exits, loading doors, and seals for

abrasive losses.

X

ELEVATOR

The abrasive elevator is usually an endless belt and bucket design that conveys the blast media

(steel grit or steel shot) upward from the bottom of the cabinet into the separator system forclassification. Usually the head section (top of the elevator assembly) has tensioning bolts for

proper alignment and belt tension.

The boot section (bottom elevator assembly) can be fed by gravity hoppers or auger assemblies.

RULES OF THUMB:

If the elevator makes clanging noise while operating, itusually means the belt tension is too loose. Tighten thehead section take-up bolts.


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Cast malleable iron buckets are most efficient onelevators.

Multi-ply heavy-duty rubber belting 3/8" to 1/2" thick ismost efficient.

Figure 1.9 Cycle of abrasive through blast cleaning system.

Table 1.5 Abrasive handling system maintenance check list.

Abrasive Handling System Maintenance Check

List

DAILY WEEKL

Y

MONTHL

Y

1. Storage hopper, feed spouts, screws, etc. Inspected

and scheduled for repairs or replacement, if the

cycling of the abrasive is retarded in any way.

X

2. Elevator belt check for:

a. Tension

b. Alignment of pulleysc. Worn or missing buckets

d. Splice condition

X

XX

X

3. Check sprockets and drive for tension, alignment,

keys, loose set screws, and bearings.

X

4. Check abrasive control valve for free operation anddesired opening.

X


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SEPARATOR

Following the wheel, the next most important component is the separator (Figures 1.10 and

1.11). Its function is to receive abrasive from the elevator, separate the undesirable trash, fines

and dust and deliver usable abrasive to the storage hopper.

Separators accomplish this task by air washing the abrasive and are available in two types.

GRAVITY TYPE SCREEN DESIGNS

Figure 1.10 Gravity type abrasive screening system.

The abrasive is delivered by the elevator and dumped onto a pan shaped screen. This screencollects unwanted trash such as nuts, bolts, bottle caps, etc. It is important that this screen be kept

clean. The abrasive falls through the screen and collects against a hinged baffle, which is swungopen by the weight of the abrasive. The baffle is adjustable and can be raised or lowered so that

the abrasive is spread in a thin stream across a shelf located below the baffle. The abrasive flows

over the lip of the shelf and falls to a permanent baffle. Air flows through the curtain ofcascading abrasive carrying the dust and fines into the air expansion chamber. The dust is carried

on to the dust collector. The fines fall into the settling chamber and are discharged through the

"dribble tube".

The air wash separator system cleans the abrasive.

The baffles and quantity of airflow to the collector control system balance.


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ROTARY SCREEN TYPE

Figure 1.11 Rotary type abrasive screening system.

This separator operates on the same air wash principle as the gravity type except the screen isself cleaning.

The abrasive discharged from the elevator is carried by a screw conveyor to the inside of a rotary

screen. The outside and inside of the screen contain flights that operate like a screw conveyor.Trash or undesirable material that will not pass through the screen is carried the length of the

screen and discharged at the trash spout by the inside flights. The outside flights keep the

abrasive from piling up against the bottom of the screen. The baffles distribute abrasive and finesfalling through the screen across the full length of the separator. An adjustable regulating baffle

commonly referred to as the sliding 2/3 baffles accomplishes uniform distribution. Adjustable

counter weights provide backpressure on the swing baffle to spread the abrasive into a thin

curtain the full length of the baffle.

CFS ABRASIVE SEPARATOR

The role of the abrasive separator in the blasting operation is to remove sand, scale, abrasive

fines and other contaminants from the abrasive operating mix so that only clean abrasive,


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properly sized, is returned to the blast wheel for reuse. The degree of success of the separator in

performing this operation in a large measure determines parts life, abrasive consumption, thetype of finish given the work being blasted, and the speed and quality of cleaning. Although

there are two general types of air wash separators used on blasting machines - the gravity and

compensating-flow (CFS) - discussion here will be centered upon the CFS type because of its

more general usage and higher efficiency. The CFS separator is designed to utilize compensatingflow to present a full-length curtain of material to the air washing currents. This uniform low-

velocity curtain permits a more thorough air washing of abrasive. It is designed so that abrasivemoves on abrasive, not the separator parts. The overhead rotary screen removes any tramp metalfrom the abrasive. It also spreads out the abrasive across the full length of the separator. Two

baffles, as shown in Figure 1.12, a fixed sliding baffle and an adjustable swing baffle are utilized.

When properly adjusted, the baffles permit only a full width curtain to be presented to the aircurrents.

RULES OF THUMB:

Maintain a full-length curtain for effective cleaning ofblast.

All abrasive in storage hopper should be free of fines anddust.

If good abrasive is discharged from fines, trash or rotarydrum trash adjustments are required in the separator.

If excessive dust is coming from blast cabinet, it usuallyindicates separator adjustment is required or dustcollector system is not working properly.

Proper balance in the system is accomplished by adjustment of the 2/3 baffle, counter weights,

fixed baffle or airflow gate.


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Figure 1.12 CFS (Compensating Flow Separator) abrasive separator.

Table 1.6 Separator maintenance check list.

SEPARATORS DAILY WEEKLY

MONTHLY

1. Clean scalping screen. X

2. Check scalping screen for holes. X

3. Check shed plates, baffles for wear. X

4. With machine in blasting cycle, check abrasive flowat point of separation (orifice) to make sure it is

uniformly spread over the entire orifice.

X

5. Make sure dribble valves are in place on refuse

pipes or tubes from separator and are workingproperly.

X

(check separator discharge for usable abrasive.)


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DUST COLLECTOR

This is basically a "king size" vacuum cleaner that provides airflow for

the separator and dust removal from the cleaning machine cabinet andelevator. Air drawn (Figure 1.15) into the collector passes through a filter

medium - usually fabric bags or cartridges. After passing through the

filters, air is exhausted at the blower discharge. Dust is conveyed from

the cleaning machine to the collector via high velocity airflow in theduct. The velocity of this air must be 3000-4000 ft/min (900-1200

m/min) to maintain the contaminants in suspension. Upon entering the

collector cabinet, the velocity is greatly reduced causing larger particlesto drop from suspension in the air stream and fall into the dust hopper.

Dust collectors that initiate dirty air coming into the top of the dust

collector and leaving out the bottom of the dust collector are said to havea down draft.

Figure 1.13

Cartridge-type

dust collector.

Figure 1.14 Schematic of a typical dust collection system.


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Figure 1.15 Dust collector up draft concept of operation.

Dust collectors that initiate dirty air coming into the bottom of the dust collector and leaving outthe top of the dust collector are said to have an up draft.

The smaller particles continue until they impinge on the filter media surface. This portion of the

collector is referred to as the "dirty side." The air (less contaminants) passes through the filter

media and is exhausted at the blower. This is referred to as the "clean air side." As the processcontinues, more large, heavy particles fall into the hopper and lighter particles build up on the

dirty side of the filter media. The buildup results in reduced air flow and increased pressure dropacross the media referred to as the "filter differential pressure."

Dust collectors remove particulates from the air using the same principle as a home vacuumcleaner.

The efficiency of the collector decreases as the dust builds up on the filters and differentialpressure increases. Various methods are used to control this buildup:

MECHANICAL SHAKER

These are used only on fabric bag type collectors. They employ a mechanism that shakes thebags, permitting the contaminants to drop off and fall into the hopper. This must be done when

the collector's exhaust blower is off. The electrical controls are usually designed to automatically

start the shaker when the blower is stopped and to run for a preset time. Manual control is alsoavailable to override the automatic. The length of time for bag shake is adjustable.

NOTES

Shaker-type bag houses should have hopper emptied twotimes per 8-hour shift.


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Anytime dust collector has a sealed fines container underthe slide gate, keep the slide gate open.

If no sealed container exists under the slide gate, keep itclosed.

If belts squeak at motor start-up, tighten them.

Make sure dust collector has a pressure differentialsensing device.

Figure 1.16 Mechanical shakers.

REVERSE PULSE JET

The reverse pulsejet is used in both fabric bag and cartridge collectors to remove accumulatedparticles from the filter media. A blast of compressed air (Figure 1.17) is released from a nozzle

into a venturi directed downward in the filter. The venturi pulls in secondary air, increasing the

pulse volume. This sudden pulse of reverse airflow flexes the filter media, causing theaccumulated particles to drop off. An adjustable timer is provided to vary the pulse cycle time

depending on the rate of build up on the filter. The air manifold supplying the nozzles must be

maintained at 90-100 psi (600-700 Kpa) in order to ensure effective operation.


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Figure 1.17 Air blast system used to clean dust filters.

Figure 1.18 Basic component of a dust collection system.

AIR PRESSURE SENSING DEVICES

The three types of differential air pressure sensing devices are:

1. ManometerA U-tube with fluid which measures (in inches of water column) thepressure differential between clean air vs. dirty-air side of dust collector.

2. MagnahelicGage measures the inches of static pressure between clean air and dirty air


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side of dust collector.

3. Photo-HelicMeasures the inches of static pressure between clean air and dirty air sideswith pulse upon demand HI/LO automation to clean elements as required by

manufacturer. This pulse action begins when elements achieve high-end static setting andcontinues until the low-end static setting is reached. It then stops until repeated

RULE OF THUMB:

Install and use a differential air pressure-sensing device on alldust collection systems.

A Magnahelic/Photo-Helic pressure-sensing device is required, usually mounted on the exteriorof the collector cabinet to indicate the differential pressure across the filter media. Each

manufacturer of dust collectors has a recommended HI/LO range for the most efficient operation.

It is recommended that an air pressure regulator be located on all air feed lines to the Dust

Collector utilizing air pulse to allow control of pulsing pressure in many situations.

Table 1.7 Dust collector maintenance check list.

DUST COLLECTOR DAILY WEEKLY MONTHL

Y

1. Inspect area around blast cleaning unit to see that it

is free of dust.

X

2. Check all duct work for leaks. X

3. Inspect blast gate settings to see that they areunchanged.

X

4. Take manometer reading. X

5. See that hoppers are empty. X

6. Check fan belts. X

7. Inspect fan vanes for wear. X

8. Check shaker or rapper mechanism while in

operation.

X

9. Check bag house or filter compartment whileshaking or rapping.

X


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NOTES

When starting up a dust collector with new bags orcartridges, do not shake or pulse until 3" of staticpressure is registered. It is good to pre-coat filters withdust when new to reduce airflow temporarily to prevent

damage to the filters or overload on the fan motor.

Dust collector should be located within 50' of the blastmachine.

If good abrasive continues to go to dust collector, add anabrasive line trap between the machine and dustcollector.

When you find good abrasive in the dust collector hopper,you can be assured it is in ductwork. Clean ductwork.

Make sure clean air inlet vents on blast cabinet are notrestricted.

All dust collectors have a highly volatile nature and mustbe emptied two times per shift.

GENERAL OPERATIONAL PRACTICES

The following is a list of some safe standard operating practices, but are not intended to be all-inclusive.

Always lock out electrical power when performing maintenance.

Stay clear of pipe while conveyor rollers are operating.

High noise levels may impair hearing. Stay clear of air discharge area. Avoid extendedexposure in close proximity to machinery that exceeds safe noise levels.

Abrasives that escape at high velocities can cause harm. Do not start the blast wheelsuntil a pipe fills the blast cabinet vestibule and seals. Make sure the proper size seals areinstalled before turning on the system. Wear eye protection at all times.

Keep sparks and open flame away from the dust collector. Dust may be explosive.

Do not activate the blast wheel(s) or shot gate(s) while loading abrasives. Damage tobuckets can result if elevator is not running during loading. Turn elevator on before

loading abrasives into the system.


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ADDITIONAL COMPONENTS AND FEATURES

1. AMMETER

The ammeter is the only instrument that will register the efficiency of the blast wheels. Each

wheel unit is equipped with its own meter that measures the current drawn by the wheel motor.The current is proportional to the amount of abrasive thrown by the wheel. Each motor size has a

specific full load current rating. (See Wheel Ampere Chart below). When the ammeter indicatesthe wheel motor is pulling full load current, the wheel is throwing the maximum amount ofabrasive. If the wheel is pulling less than full load, it is not being used to its full capacity. Thereare two (2) types of meters as follows:

a. Analog TypeThis style registers the actual motor load with a needle on a graduated scale.

This style must be calibrated regularly via a thumbscrew and can drift out of calibration.

b. Digital TypeMotor load amperage is displayed digitally on the meter face. Digital meters are

available with LED or LCD display.

WHEEL AMPERE CHART

Table 1.8 Ammeter Readings

440 VOLTS 220 VOLTS

H.P. NO LOAD FULL LOAD NO LOAD FULL LOAD

10 5 13 10 26

15 7 19 14 38

20 9 27 18 54

25 10 31 20 62

30 12 36 24 72

40 17 49 34 98

50 20 61 40 122

60 25 73 50 146

75 33 94 66 188

100 41 116 82 232

NOTES

Each wheel unit must have its own meter.


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All wheel units must operate at full load amps.

The difference between the no load amps and full loadamps is the available cleaning amps.

2. VESTIBULE AND SEALS

Most blast cabinets have inner and outer seals mounted on vestibules on each end. The vestibules

provide a space between inner and outer seals. The space between the seals is connected to lower

portion of the cabinet so that abrasive that escapes the inner seal can run back into the cabinet.

Seals come in different materials and configurations. They can be sheets of natural rubber,rubber sunburst segments or nylon brushes.

a. Sunburst TypeConventional pipe machines are designed to run small diameter as well as

larger diameter pipes. In order to maintain a positive seal, each machine must go through an

entry and exit vestibule seal change. A particular seal will cover approximately 4" increment andseal pipes ranging in sizes from 2" up through the maximum diameter it is designed for

(approximately 36", 48" or 60"). This design is a typical sunburst style utilizing an inner and

outer arrangement of replaceable rubber segments.

NOTE

Seals must be maintained for proper machine ventilation aswell as abrasive retention.

b. Brush TypeBrush seals allow air flow through the seal yet contain the abrasive in the cabinet.

Brushes are designed to fit one size pipe. Steel adapters are required for each pipe size. Primary

steel adapters adapt from maximum pipe size to a smaller pipe range i.e. primary adaptor 36''-48''allows secondary adapters for each size in the range from 28-34. The 36"brush seal mounts

directly on the primary adaptor.

There are two brush seals at each interface: two at the cabinet-to-vestibule interface, two at

the vestibule-to-outside interface. An abrasive resistant rubber sheet in the blast area

protects the innermost brush seals.

MAINTENANCE NOTE

Rotate the brushes approximately 1/8-turn periodically tospread out wear around the brush. This will increase the life ofthe brush seal.


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Figure 1.19 Typical Rubber or Brush Sequence Seal.

NOTE

If seals are too tight, conveyor may have difficulty pushing thepipe through the machine. Increase the diameter of the hole ormake radial cuts around the hole to reduce the drag on thepipe.

c. Sheet Rubber TypeMany blast machines use rubber sheet for seals. The normal material

used for this purpose is natural rubber. The rubber seals are attached to the vestibule with bolts orwedges. A hole, which is slightly smaller than the outside diameter of the pipe, is cut in the

rubber sheet to match the pipe as it passes through the machine. The hole diameter is usually 2"smaller than the pipe diameter.

d. Combination Brush & Sheet Rubber TypeUse brush seals at the vestibule-to-outside

interface and use sheet rubber for the cabinet-to-vestibule interface. This allows airflow to the

vestibule while the more abrasive-resistant rubber is in the blast area. Both of these help containthe abrasive.

3. CONTROL SYSTEM PACKAGES

The blast machine typically has a separate control panel that is dedicated to the operation of itsmotor components. There are several types of controls as follows:

a. Relay Logic Type. This is the most commonly used system and is simply electromagneticcomponents and relays wired to allow the functions to operate sequentially. The control


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panel will have operator push buttons located on the panel door and possibly will have

remote operation buttons in the systems main control line.

b. "PLC" Logic Type. This is the new technology that operates the machine functions via a"PLC". This type of system can be utilized to control wheel speed, abrasive flow andother functions with simply a program input. It also can supply system repeatability and

performance guarantee with printed documentation if desired.

4. ABRASIVE LEVEL MONITORING SYSTEM

This feature is designed to help the operator control a proper level of abrasive in the

machine to insure a well rounded operating mix. A bin level probe is mounted in the

abrasive storage hopper to monitor the abrasive level. This component can be integrated

with lights in the control panel to indicate levels or can be integrated with an automatic

abrasive adding unit.

NOTE

This eliminates the guesswork on the amount of abrasive inthe machine.

5. ABRASIVE FLOW CONTROL SYSTEMS

Each wheel unit must have its own valve to meter the flow of abrasive. There are several types asfollows:

a. Manual/Mechanical. This type is either a manually operated or air cylinder operated

dipper valve that opens to a pre-set position to achieve full load amps and then closes tostop the flow.


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Figure 1.20a Manual/Mechanical abrasive flow control valve.

b. Automatic Magnetic Variable Abrasive Flow Control. This style is utilized with a

"PLC" and can variably change the flow of abrasive to any degree very precisely via aprogram insert. This allows the abrasive flow to be varied for maximum efficiency.

Figure 1.20b Automatic magnetic variable abrasive flow control valve.


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RULE OF THUMB:

All wheels must operate at full load amps.

6. WHEEL DRIVES AND SPEED CONTROL

There are two (2) types of wheel drive systems as follows:

a. Unit Bearing Type. This is the most common style that utilizes sheaves and belts whichconnect the motor to the unit bearing which is attached to the wheel.

Direct Drive. This is the newer technology that allows the motor to be directly connected to

the wheel itself.

b.

NOTE

Direct drive eliminates loose belt problems.

c. Variable frequency Drives/Variable Wheel SpeedThis concept allows the variablecontrol of the wheel speed, which will vary the velocity of the abrasive being thrown.

This can be of value when variations are present in pipe sizes as well as profiles to beachieved.

7. CABINET LINER PACKAGES

The typical blast machine is fabricated from mild steel that can vary in thickness from 1/4" to1/2". There are two types of internal lining packages to maximize the abrasive wear resistance asfollows:

a. Manganese Lining. This is a special (11% to 14% Hatfield) work hardening steel thatgives good results against a nominal abrasive in the hardness range of 40 to 50 RC (Steelshot or soft grit).

b. Cast Chrome Molly Lining. This is the premium design in which cast tiles are bolted tothe inside surfaces and have excellent results against hard grits above 50 RC. This lining

will typically out last manganese by a factor of 15 to 1. The cost of cast linings is

considerably higher than manganese plate. Economics will play an important role in thedecision to use this type of lining.

NOTES

When using steel shot, use a manganese-lined cabinet.


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When using hard grit, use a cast chrome molly-linedcabinet.

MAINTENANCE PROGRAM SUGGESTIONS

MAINTENANCE

All blast cleaning equipment is self destructive, but the key to low cost operations isPREVENTIVE maintenance. Preventive maintenance anticipates and schedules repairs, andtrains operating and maintenance personnel in the proper use and repair of equipment.

Leaks of any nature are not conducive to economy as the abrasive is lost. Abrasive consumption

is high and hazardous conditions are created for personnel and surrounding equipment.

SUMMARY

Proper surface preparation is an important part of a good pipe coating operation. To ensure

equipment is operating at peak efficiency, be sure to:

Check daily: Wheel components, ammeter wheel flow readings, dust collectormanometer readings, abrasive curtain at separator and blast patterns.

Adjust pipe rotation so that forward travel of pipe through blast machine does not exceedlength of blast pattern.

Maintain a full abrasive curtain in the air wash separators.

Maintain operating mix by making small frequent additions of new abrasive. Never letabrasive feed hopper fall below 2/3 full.

Maintain daily records of abrasive additions, parts replaced and wheel hours operated.

Screen analysis: One per week at the very minimum; check operating mix, discard fromseparator and scalp screen.

Check your mastery of lesson 1


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Surface Preparation

ABRASIVE MEDIA

Shot

Grit

Operating Mix

Abrasive media provides the finish to the surface being cleaned. The media falls into two

categories: shot and grit. Both are manufactured to specifications in a variety of sizes and

specific hardness ranges, enabling the user to obtain the desired finish. This lesson addresseshigh-carbon cast steel abrasive media only.

High-carbon cast steel shot and grit are manufactured to the following Society of Automotive

Engineers Specifications:

SAE J827: Covers material composition and hardness (shot).

SAE J444: Covers size and new material screening (shot and grit).

SAE JI993: Covers material composition and four (4) hardness ranges (grit).

SHOT

Shot is manufactured in a round shape. Its standard designation is the letter "S" followed by anumber to indicate the size. The number is the approximate diameter, in inches, of the nominal

screen size. For example; "S-280" is shot with a nominal size of approximately .028 inches in

diameter. The higher the number the larger the shot size. The standard hardness of shot is 40-51HRC.

GRIT

Grit is crushed shot, angular in shape. Its standard designation is the letter "G" followed by a

number to indicate size. The number is the nominal screen size with an opening the same as the

grit number or size. For example; "G-25" is grit with a nominal size of approximately .0278inches on a #25 screen.

RULE OF THUMB:

Steel shot is usually used in sizes from S-280through S-390 for cleaning pipe.


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RULE OF THUMB:

Steel grit is usually used in sizes from G-50 throughG-16 for cleaning pipe.

NEW SHOT AND GRIT

SIZE SPECIFICATIONS

S.A.E. SHOT SCREENING SPECIFICATIONS

Screen opening sizes and screen numbers with maximum and minimum cumulative percentagesallowed on corresponding screens.

SAE Size No. Shot Tolerances Screen Opening

All Pass No. 4 Screen .1870

90% Min on No. 6 Screen .1320

S-1320




S-1110




S-930




S-780


All Pass No. 8 Screen .0937S-660



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85% Max on No. 14 Screen .0555

S-550





S-460





S-390





S-330





S-280





S-230



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S-170





S-110





S-70


S.A.E. GRIT SCREENING SPECIFICATIONS

Screen opening sizes and screen numbers with minimum cumulative percentages allowed on

corresponding screens.

SAE Size No. Grit Tolerances Screen Opening



G-10




G-12


G-14 All Pass No. 10 Screen .0787


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G-16




G-18




G-25




G-40




G-50




G-80




G-120


G-200 All Pass No. 80 Screen .0070


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All Pass No. 120 Screen .0049G-325


GRIT HARDNESS

Grit is available in four (4) SAE hardness ranges. Each manufacturer uses a slightly different

letter designation to identify the four (4) SAE hardness ranges for their product.

The four SAE J1993 hardness ranges are as follows (Hardness ranges listed are from standardhardness through higher hardness.)

(1) Grit size designation from SAE J444

a. HCS G(1)S - The hardness ranges shall be 40-51 HRC.

b. HCS G(1)M - The hardness range shall be 47-56 HRC.

c. HCS G(I)L - The hardness range shall be 54-61 HRC.

d. HCS G(1)H - The hardness shall be 60 HRC minimum.

90% of the hardness readings shall be within the specified range.

EXAMPLE:

HCS G-25-L indicates a high-carbon cast steel grit meeting the G-25 requirements in SAE J444,

with a hardness designation of L (54-61 HRC).

OPERATING MIX

Cleaning and surface finish is obtained by numerous impacts of the abrasive media. During the

impacting process, the abrasive media is subjected to very high stresses that cause eventual

failure through fracture and fatigue, creating a range of particle sizes. The mix of various particlesizes is referred to as the operating mix or work mix. A properly balanced mix is essential for

effective results. Larger particle sizes are required to remove rust and scale while smaller sizesare needed to clean pits and minute crevices. The formation of an operating mix is a continuous,

ongoing process. Once it has been established, it can be controlled by frequent small additions ofnew, original size abrasive and removal of undesirable fines.

RULE OF THUMB:


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Maintain operating mix by periodically makingsmall additions of new abrasive and removing allundesirable fines from the mix.

A number of variables affect abrasive usage and the operating mix, such as:

Velocity of abrasive hitting the work

Hardness of the work being cleaned

Hardness of the abrasive media

Type of anchor pattern desired (profile)

Improper abrasive additions

Separator take out size

Blast cabinet leaks

Dust collector abrasive loss

SCREENING

To ensure the operating mix is maintained, a screen analysis should be taken frequently. This is

done by using a set of standard screens or sieves which are stacked on top of each other with the

largest screen opening on top and decreasing in size to the bottom. A pan on the bottom of the

stacked screens catches whatever passes the smallest screen. A known quantity of operating mix,by weight or volume, is placed on top screen. The stack is shaken for 5 minutes to allow the

abrasive to sift through the screens. The stack of screens should be tapped on a hard surface

frequently when shaken, to help the sifting action. The volume of abrasive remaining on eachscreen is then recorded. The amounts are compared to the original quantity to arrive at the

percentage remaining on each screen.

SAMPLING PROCEDURES

Obtaining samples to be screened is a simple process. An operating mix sample can be obtained

from the separator abrasive curtain below the point of airflow through the separator. Use asuitable receptacle that can be drawn completely across and through the abrasive curtain flow,capturing a representative sample after the point of air wash separation. The sample size required

is lb. It is recommended that a sample be taken from the separator discard (dribble pipe) at the

same time as the operating mix sample is taken. This sample is a simple catch test of materialdiscarded by the separator.

Once screened, the operating mix sample will verify if the mix is balanced with proper size

distribution. The separator discard sample screen results will indicate if the separator isdiscarding usable abrasive.


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It is also important to do a catch test of the rotary drum screen discard on a daily basis. A screen

test will indicate if usable abrasive is being discarded due to the screen being plugged by paper

or trash material.

Periodically, samples should be taken from the dust collector dust discard and screened to see ifusable abrasive is being lost to the collector.

When taking samples of new abrasive to verify size, be sure to collect the sample from the mid-

portion of the container in which the abrasive was packaged. This will cut down on segregationof sizes in the container that occurs when material is transported from manufacturer to user.

RULE OF THUMB:

A balanced operating mix can vary depending onfinish required; take out size, hardness of

abrasive, new material additions, and machineseparator capability.

RULE OF THUMB:

Guidelines for a balanced operating mix: 45-55% of sample will be the cumulated% on the nominal screen. The take out screen would have an individual reading of2 to 5%.

EXAMPLE:

SCREEN

SIZE

SHOT

S- 280

GRIT

G-25-S

#16 - .0469

#18 - .0394

#20 - .0331

#25 - .0278 NOMINAL NOMINAL

CUM % 45 TO 55NOMINAL SIZE


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SCREEN

SIZE

SHOT

S- 280

GRIT

G-25-S

#30 - .0234

#35 - .0197

#40 - .0165

#45 - .0139

CUM % 40 TO 53MID RANGE SIZE

SCREEN

SIZE

SHOT

S- 280

GRIT

G-25-S

#50 - .0117 TAKE OUT TAKE OUT

IND % 2 TO 5TAKE OUT SIZE

Once an operating mix is established, it can be maintained with small additions of new abrasive,

removal of undesirable fines, and regular screen analysis. The removal or take out size represents

the undesired fines remaining in the mix.

If undesirable fines are not removed from the operating mix, they could be deposited on the pipeand may contaminate the steel surface. This is visible as dark particles on the backside of coating

chips removed from the pipe.

RULE OF THUMB:

Abrasive larger than the established take out sizeshould not appear in separator fines discard(dribble pipe).

BACKSIDE CONTAMINATION

The pipe coating industry has always maintained concerns regarding backside contamination that

remains on the pipe after surface preparation. This backside contamination is normally the result

of an expanded operating mix with too many fines. This is normally the result of a


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malfunctioning separator or dust collector, or a combination of both.

RULE OF THUMB:

Backside contamination is usually the result of toomany undesirable fines in the operating mix.

ABRASIVE CONSUMPTION

Abrasive consumption depends on the breakdown characteristics of the abrasive, velocitythrown, abrasive flow rate, horsepower of wheels, take out size, and leaks or loss at the machine.

Abrasive consumption should be monitored by usage per wheel hours. Keep track of wheel hours

run and abrasive added over a given time period. This will establish consumption by wheel hour.

RULE OF THUMB:

Standard hardness (40-51 HRC) shot consumptionshould run approximately lb. per horsepower perwheel hour.

RULE OF THUMB:

Guideline abrasive consumptionrates per lb. by horsepower,hardness and type.

S=STEE

L SHOT

G=STEEL GRIT BY

HARDNESS

H.P

.S GS GM GL GH

10 5 5.1 6.3 9.6 37.5

15 7.5 7.7 9.4 14.4 56.2

20 10 10.3 12.6 19.3 75


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25 12.5 12.8 15.7 24.1 93.7

30 15 15.4 18.9 28.9 112.5

40 20 20.6 25.2 38.6 150

50 25 25.7 31.5 48.2 187.5

60 30 30.9 37.8 57.9 225

75 37.5 38.6 47.2 72.3 281.2

100 50 51.5 63 96.5 375

This general guideline can bedifferent due to abrasive loss andwheel velocity.

RULE OF THUMB:

Standard "S" hardness abrasive breaks downslower than harder abrasive.

CLEANING EFFICIENCY

Cleaning efficiency is a direct result of size of abrasive used, the velocity of the abrasive, andamount thrown per minute. For efficient cleaning, it is important to throw as many pellets as

possible from new material size through the established take out size. The more pellets thrown

using a balanced operating mix gives coverage which increases speed of cleaning.

A balanced operating mix provides a greater number of impacts. See charts below on number of

pellets of shot and grit by size in new material. As you can see, as the material down sizes in a

mix, the pellet count per pound goes up.

RELATIONSHIP OF SHOT/GRIT SIZE TO COVERAGE

APPROXIMATE PELLETS PER LB.SAE GRIT SIZE

(MID RANGE)

SAE SHOT SIZE

(MID RANGE)GRIT SHOT


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G-10 S-780 7,400 8,000

G-12 S-660 12,500 14,000

G-14 S-550 23,200 26,000

G-16 S-460 40,500 45,000

G-18 S-390 54,500 65,000

S-330 110,000

G-25 S-280 175,000 210,000

S-230 360,000

G-40 S-170 440,000 520,000

G-50 S-110 1,300,000 1,700,000

G-80 S-70 4,400,000 6,000,000

SUMMARY

Proper surface preparation is an important part of a good pipe coating operation. To ensure

equipment is operating at peak efficiency, be sure to:

Maintain a full abrasive curtain at the air wash separators.

Maintain operating mix by making small frequent additions of new abrasive. Never letabrasive feed hopper go below 2/3 full.


Screen analysis: one per week at the very minimum; check operating mix, discard fromseparator and scalp screen.



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Defining Blast Cleaning and Profile

DEFINITION OF BLAST CLEANING

Blast cleaning can be defined as an impact-cleaning operation in which the work surface ispounded by successive impacts of abrasive. An effective blast cleaning operation is a function of

proper abrasive selection, shot or grit, blast wheel speed, and proper work-mix size distribution.

DEFINITION OF PROFILE

Surface profile, which is also called etch, anchor pattern or texture, is a measurement of surface

roughness resulting from abrasive blast cleaning. The height of the surface profile is measuredfrom the bottom of the lowest valleys to the tops of the highest peaks. The profile depth or height

is dependent upon the size, type (shot or grit), and hardness of the abrasive, particle velocity and

angle of impact, hardness of pipe surface, and amount of size distribution in recycled work mix.

DEGREES OF CLEANING

Blast cleaned surface cleanliness is categorized by NACE (National Association of CorrosionEngineers) and SSPC (Steel Structures Painting Council) into four (4) grades. The four grades

are defined as follows:

BRUSH-OFFBlast Cleaned Surface Finish:

When viewed without magnification, is a surface from which oil, grease, dirt, loose rust, mill

scale, paint, or coatings can be removed. Tightly adhering mill scale, rust, paint, and coatings arepermitted to remain if they have been exposed to the abrasive blast pattern, and numerous flecks

of the underlying metal are uniformly distributed over the entire surface. REF: NACE No. 4and/or SSPC - SP7.

COMMERCIALBlast Cleaned Surface Finish:When viewed without magnification, is a surface from which oil, grease, dirt, rust, scale, and

foreign matter have been completely removed. All rust, mill scale, and old paints or coatings

have been removed except for slight shadows, streaks, or discoloration caused by rust stain or

mill scale oxide binder. At least two thirds of the surface shall be free of all visible residues. Theremainder shall be limited to light discoloration, staining, or light residues mentioned above. If

the surface is pitted, slight residues of rust, paint, or coatings are found in the bottom of the pits.

REF: NACE No. 3 and/or SSPC - SP6.

NEAR-WHITEBlast Cleaned Surface Finish:When viewed without magnification, is a surface from which all oil, grease, dirt, mill scale, rust,

corrosion products, oxides, paints, coatings, or any other foreign matter have been removed

except for light shadows, streaks, or slight discoloration of oxide bonded with metal. At least95% of the surface area has the appearance of a white metal blast and the remainder of the area islimited to slight discoloration. REF: NACE No. 2 and/or SSPC - SP10.

WHITE-METALBlast Cleaned Surface Finish:


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When viewed without magnification, is a surface with a gray-white metallic color, roughened to

a suitable profile for coatings. The surface is free of all oil, grease, dirt, mill scale, rust, corrosion

products, oxides, paint, and any other foreign matter. REF: NACE No. 1 and/or SSPC - SP5.

There are visual standards available through the NACE and SSPC which clearly show each ofthe four (4) grades. The visual standards are helpful tools in determining degree of cleaning.

SURFACE FINISH AND PROFILE

Surface finish and profile on the work piece is created by the size of the shot or grit thrown and

its velocity. The larger the abrasive particle, the harder it hits, transferring that energy to the

work piece. As each particle hits, it indents or etches the surface, leaving a profile. The chartbelow will help illustrate the impact relationship by size at standard velocity.

The above chart shows impact value by size.

Example: G-80 grit and S-70 shot have an impact value of 1. G-18 grit and s-390 shot have an

impact value of 100. The chart illustrates that G-18 and/or S-390 hit the work surface 100 timesharder than the smaller G-80 or S-70.

RULE OF THUMB:

Large shot or grit results in fewer pelletsper pound and effects coverage.

RULE OF THUMB:


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At standard velocities, large shot or gritdelivers more impact than smaller sizes(more profile).

RULE OF THUMB:

When selecting an abrasive size (shot orgrit), always choose the smallest sizepossible to give the desired cleaningprofile results.

PROFILE

Profile on the pipe surface is critical for proper adhesion of the coating. Profile is created by theshot and grit thrown by the wheels. Shot leaves a rounded profile and grit leaves a sharp orpeaked profile. Larger sizes of abrasive leave a higher profile. For pipe coating, grit is preferred

over shot for the type of profile desired. Hard grit delivers a more distinct profile than softer grit

due to its hardness and break down characteristics. Also, when blasting hard pipe the harder grit

impacts the hard surface better.

RULE OF THUMB:

Hard grit creates a sharper profile thensofter grit or shot.

RULE OF THUMB:

Various profiles achieved with shot andgrit

1 Mill Profile 1.5 Mil Profile

G-80 G-50

S-110 S-170

2 Mil Profile 2.5 Mil Profile


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G-40 G-40, G-25

S-230 S-280

3-4 Mil Profile

G-25, G-16

S-330, S-390

This is profile guideline information only.Actual profiles could be significantly

different due to abrasive hardness, wheelspeed, angle of impact, or hardness of thesurface being blasted.

SUMMARY

Proper surface preparation is an important part of a good pipe coating operation. To ensureequipment is operating at peak proficiency, be sure to:


Screen analysis: One per week at the very minimum; check operating mix, discard fromseparator and scalp screen.



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Additional Surface Preparation

This chapter is about the surface treatment of pipe prior to application of fusion-bonded epoxy

coatings. It includes a short section on cleaning pipe prior to blasting as well as washing/surfacetreatment after blasting. Its purpose is to:

Discuss background reasons for considering additional surface preparation.

Describe the mechanical steps in acid wash and in surface treatment.

Review options and plant layout.

BACKGROUND

There is no question that a contaminant on a steel surface will result in reduced performance

properties of ALL coatings. This is also true of fusion-bonded epoxy coatings.

This chapter is only a brief overview of some of the contaminants that may be found on steelpipe surfaces. For more information on this subject see the Tenneco Gas MQ-845, "Surface

Contamination: Sources and Tests," and NACE Publication 6G186, "Surface Preparation of

Contaminated Steel Surfaces."

CONTAMINANTS

OIL AND GREASE

Oil and Grease can come from a variety of sources--equipment in a pipe manufacturer's plant,

railroad ties, port or ship's tackle, the applicator's handling and conveying equipment, orcontaminated abrasive. If the pipe is in a generally rusted condition, an unrusted area will likely

be contaminated with grease or oil.

CONTAMINATION

A SLOW DAWNING

"We first suspected a contamination problemwhen we ran some blast cleaned pipe out inthe yard. After two days in the rain we noticedthe pipe hadn't rusted."

1979 Germany

"We found the contamination problem byaccident. We had some blast cleaned panelsstored near a steam bath. After a few hourssome panels got rust spots - some didn't."


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1981 Newcastle Upon Tyne

"I know we're doing a good job of cleaning.I've had blast cleaned parts in my garage formonths and they didn't rust."

1983 Indiana

Recirculating blast-cleaning machines used in pipe coating mills are very effective tools forspreading concentrations of contaminated material over very large surface areas. Therefore, it is

essential to remove oil and grease prior to the blast cleaning process. Solvent or detergent wash

or steam cleaning are effective methods. If detergent wash is used, employ a thorough rinse afterthe washing operation to remove all detergent.

WATER-SOLUBLE OIL

Water-soluble oil is used during the manufacture of ERW pipe. The term water-soluble oil is a

misnomer. It is actually an oil/water emulsion, which contains microscopic droplets of oil

suspended in the water. Freshly rolled ERW pipe will have a sooty film (often called carbon or

smut) on the surface. This film is composed of an oil and mill scale mixture and weathers awayfairly quickly when exposed to the elements. Repeated wetting (approximately 30 days) of thepipe accelerates the weathering process. Steel pipe manufacturers remove it by detergent

washing prior to shipment.

Field experience indicates that acid wash after mechanical blasting is also effective to removesmut.

ETHYLENE GLYCOL

Anti-freeze materials such as ethylene glycol are used to prevent freezing of hydro test water.These materials often get on the pipe and must be treated like water-soluble oil.

RULE OF THUMB:

"...visual appearance of a steel surface,immediately after blast cleaning, is anunreliable means of identifying either thepresence or the type of contaminant."NACE Publication 6G186

FERROUS SALTS

An example of ferrous salt is table salt also called sodium chloride or NaCl. However, ferroussalt contamination, includes a whole class of inorganic compounds such as sulfates and nitrates.

These compounds possess a common property with table salt - they can cause a reduction inadhesion of the coating to the steel and/or porosity (foam bond) in the coating itself.


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Synthetic Sea Water

sodium chloride (NaCl) 2815 g

potassium chloride (KCl) 67 g

magnesium chloride (MgCl26H2O) 551 g

magnesium sulphate (MgSO47H2O) 692 g

calcium chloride (CaCl2) 145 g

water 100 liters

Figure 4-1 Seawater is a common source of salt contaminations.

How does salt contamination get on the steel surface; where does it come from?

Common sources of salt contamination include salt used for road deicing and from seawater.Seawater contamination can be a result of direct contact with seawater or from ocean side

storage of either the rolling plate or the pipe itself. Another possible source of salt contaminationis acid rain.

Figure 4.2 Acid rain can also result in salt contamination of the pipe.

SURFACE TREATMENTS

There are many kinds of pipe surface contaminants that cannot be adequately removed by blast

cleaning. For this reason, many in the pipe coating industry believe that additional surface

preparation steps need to be considered. Surface treatments now in practice include:

Cleaners

Cleaners are materials and processes such as high-pressure water, detergent, or acid washes thatremove contaminants from the steel surface. Although the intent of this process is contaminationremoval, the cleaning agents may also enhance the surface properties of the steel.


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Enhancers

Enhancers are treatments deposited on the steel surface to improve the performance properties of

coatings. In fact, the improvement may be such that it can overcome the negative effects of low-

level concentrations of contaminant. The next steps spell out in general terms the applicationprocess for an acid wash (cleaner) and for a chromate treatment (enhancer). The specific

application steps for cleaners and enhancers depend on the recommendations of the manufacturer

of the product used. Read all Health Hazard, Precautionary, and First Aid statements found in the

Material Safety Data Sheet, and/or product label of chemicals prior to handling or use.

ACID WASH (Cleaner)

Thc acid wash process is fairly simple.

1. Wet out the pipe surface with the cleaning agent

2. Let it work.

3. Rinse.

RULE OF THUMB:

The higher the pipe temperature (belowthe boiling point of water) the moreeffective the cleaning step.

The longer the dwell time - the longer thecleaning agent is in contact with the pipesurface - the more effective.

Do not let the cleaning agent dry beforethe rinse step.

The actual process conditions depend upon the chemical cleaning agent employed, the condition

of the pipe surface, and the level of contaminants. For phosphoric acid wash the following

general steps are applicable:

Blast Clean- blast clean the pipe surface to remove all mill scale. Grind to remove slivers and

other unacceptable surface imperfections before the acid wash.

Application- apply the cleaning agent uniformly over the pipe surface using either a spray orgravity feed method.

Dwell Time- with an acid wash there is a chemical reaction between the cleaning agent and the

steel. This chemical reaction is time/temperature dependent. In a typical operation, the pipe will

be at a temperature of about 110 degrees Fahrenheit (49 degrees Celsius), and the dwell time will


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be on the order of 21 seconds. Some specifications require the extension of the dwell time by one

second for each degree below the typical temperature. Check the acidity of the cleaning agent on

the steel using pH paper. It should be at a pH of two or less - indicating a strong acid.

Rinse- remove the acid wash and dissolved contaminants by rinsing. Some specificationsrequire the use of high-pressure water [500 to 1,000 psi (3500-7000 KPa)] in the rinse step. The

high pressure may be useful in removing solid particulates imbedded in the steel by the blast

cleaning process. Other specifications require a water rinse without high pressure. In any event,

the objective is removal of both the acid and contaminants. Using pH paper on the rinsed pipesurface can check this. The pH should be greater than six or at least near the pH of the water

used to rinse the pipe. Rinse additives can be used to reduce flash rust and to improve coating

performance, if required.

Dry- the pipe is then dried quickly to minimize oxidation. Techniques used are squeegee, airknife, or heating elements (gas-fired furnace). If an air knife is used, the high-pressure air supplyshould be routed through oil traps and filters to remove any contaminants.

Disposal- check with the supplier of the cleaning agent for safe disposal procedures.

An acid wash station requires a significant amount of space because of the required dwell time

between the wash and rinse steps. An example of the layout for an acid wash station follows:

Figure 4-3 Set up for acid wash station.


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Figure 4-4 An acid wash stem after final blast clean allows the surface to remain chemically

active.

Advantages of Figure 4-4:

In the case of phosphoric acid wash, there is evidence that the phosphate surface providesimproved performance in the subsequent coating.

Immediate furnace heating after acid wash rinse reduces flash rust.

Disadvantages of Figure 4-4:

There is the possibility of contamination carry through from one blast machine to thenext. See QC TESTS

The anchor pattern is not easily reestablished after grinding, unless allowable by specificconditions.


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Figure 4-5 An acid wash step before final blast clean keeps the last machine

uncontaminated.

Advantages of Acid Washing Between Cleaning Machines:

Allows ground areas to be reblasted to establish the anchor pattern.

Contamination should not carry from first machine to second.

Contamination is removed prior to final blasting.

Disadvantages of Acid Washing Between Cleaning Machines:

Many present plants are not set up with space between two blast machines.

If phosphoric acid wash is used, there is evidence that the phosphate surface does provideimproved performance in the subsequent coating. Blasting after wash may remove

phosphate coating.


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Figure 4-6 A typical surface treatment takes less space than acid wash.


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Figure 4-7 An acid wash followed by surface treatment provides cleaning as well as an

active surface for improved coating adhesion.

SUMMARY

For best performance, all coatings require a good surface for application. Chapter 1 described

aspects of mechanical treatment of the steel surface. This chapter reviewed techniques andprocedures for further improvements in surface preparation through chemical cleaning and

treatment. Plant layout can affect both productivity and product performance. Several diagramsprovide a few of the many possibilities.

Some specifications now require a chemical surface preparation step; many others mention it, butallow the applicator to make the decision.



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Pipe Heating

In the fusion bonded epoxy coating process there is a need to heat the pipe prior to cleaning and

application of the epoxy resin. The steps to compete these functions, the types of equipmentutilized and the temperature measurement procedures are as follows:

1. HEATING PRIOR TO PIPE CLEANING:The proper cleaning of the pipe surfacerequires that any moisture on the pipe be removed and the pipe surface temperature is

above the dew point to prevent reformation of water on the surface. If the surface is wetthe oxides removed in the cleaning machines will adhere again to the moist surface and

impair the coating bond. The pipe is generally heated by means of gas fired tunnel type

ovens or electrical induction coils as shown in Figures 1.1 & 1.2.

Figure 1.1


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Figure 1.2

The gas fired heater permits the pipe to pass through the center of a gas fired radiant heater or a

direct impinging flame. The temperature of the pipe is controlled by the settings on the gas fired

heater and the rate of speed of the pipe going through the heater. The heater must be coordinatedwith the conveyor stopping and starting, so as not to over heat the pipe when the conveyor is shut

down. In a similar manner the induction-heating coil can be controlled for output and the line

speed may be varied as well to increase or decrease the pipe temperature. The dew point

temperature is defined by using a sling hygrometer to determine the dewpoint temperature andthen a safety factor is added, such as 10% to ensure the pipe does not drop below the dewpoint

due to other variables. Typical preheat temperatures are generally in the 125F range. It isessential to maintain a consistent preheat temperature, joint to joint, to provide for optimum

heating control on the coating line prior to powder application. If the pipe heat prior to epoxy

powder application moves outside of the specified temperature parameters the performanceproperties of the coating may deteriorate.

2. HEATING OF PIPE PRIOR TO EPOXY POWDER APPLICATION:Epoxy powder

resins require application temperatures of 450-480F and a minimum period of time at this

temperature to wet out and cure in order to provide the specified performance parameters. The

details of this heating and curing process are described in other chapters of this training course.To heat the pipe to the specified temperature gas fired ovens or electrical induction coils are

utilized. Generally a series of 3 to 5 gas fired radiant ovens are used, that allow the pipe to pass

through the center while being heated. (Figure 1.3)


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Figure 1.3

The temperature of the pipe is controlled by the output of the ovens and the rate of travel of the

pipe passing through the oven. In a similar fashion the induction heating coils output and the

speed of the pipe are used to control the heat of the pipe.

Figure 1.4


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With the pipe heated to the required high temperatures it is necessary to have solid metal

conveyor heads between the ovens and the epoxy application booth. If rubber tired conveyor

heads are used the rubber will degrade and particles of rubber may adhere to the pipe and inhibitthe bond between the coating and the pipe surface.

3. TEMPERATURE MEASUREMENT DEVICES:The monitoring of the pipe temperatures

is essential for process control and there are generally three devices used:

A. Melt Crayon:Temperature sensitive compound that will melt at a specified temperature. The

melt crayon is touched on the pipe as it rotates along and the operator observes if the small markof material melts out and shows a sight change in color. The melt crayon sticks haveapproximate 15 F temperature range sensitivity.

B. Infrared Pyrometer:This device measures infrared radiation emitted from the pipe and

displays the pipe temperature in either degrees Fahrenheit or Celsius. The unit must be calibrated

for the degree of emissivity of the bare steel pipe that affects the level of infrared radiationreaching the instrument. The surface conditions of each pipe can vary somewhat and for this

reason this device may provide a wider indications of bare pipe temperatures. The device is moreapplicable to monitoring the temperature of the FBE coated pipe, which is much more consist, inthe level of infrared radiation emitted to the instrument. The instrument is available in either a

fixed mounted style or a hand held unit. The fixed unit can have permanent recording

attachments to document pipe temperatures. Calibration of the unit requires the use of a handheld contact thermocouple.

C. Contact Thermocouple:This instrument combines a thermocouple contact device with atemperature readout unit and provides very accurate pipe temperature readings. The contact unit

is available in two configurations that provides for temperature readings from either fixed or

rotating pipe.



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Powder Application Process and Systems

Successful application of powder coatings requires properly designed powder application

processes and pipe handling systems that will work with various powder coating formulations.

This chapter discusses the following topics:

Powder Application Properties of the coating material

Gel Time Definition, effect of temperature and temperature measuring devices.

Pick-up Time - Definition, importance of application speed.

Cure time - Definition, effect of application temperature, cool down rate and product curerequirements.

Coating thickness Factors include line speed, application temperature, gun output andelectrostatic voltage. Coating thickness can affect cure time.

Coverage Specific gravity

Powder Application Systems

Illustrations of general systems currently in use with advantages and disadvantages ofeach

Equipment elements.

Dust collectors.

Screens Operation and equipment illustrations

Magnets.

Rotary valve Illustration.

Powder gun output.

Fluid bed Purpose and illustration.

Feed lines Flow versus pressure and size.

Air dryers.


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Figure 6.1 Pipe being coated in a continuous process coating plant

Powder Application

Properties of the Coating Material

To optimize economics, it is desirable to apply powder that meets end product performancerequirements at a high production rate.

Assuming the pipe can be cleaned and heated at the desired rate, the powder application system

must have the capacity to provide the quantity of powder required to meet coating thickness

requirements.

Properties of the powder that affect application rate are:

Gel Time

Pick up Time

Cure Time

Coating Thickness

Coverage

Gel Time

Gel time is the time elapsed between powder melting and solidification. It varies withpowder formulation and application temperature. (Figure 6-2) The temperature measuring

device can affect gel time results. A typical example is shown in Figure 6-3 where aThermo-Electric Co, hotplate with an internal probe thermometer was used. The hot plate

surface temperature was also measured with a surface thermocouple and a surface

thermometer. Approximately 30F difference existed between the devices. Thisdifference results in gel time variations as shown in Fig.6-4.


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Fig 6-2 Coating material gel time varies with product and application temperature

Figure 6-3 Surface temperature may vary by as much as 40F. from gel plate internal

thermometer.


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RULE OF THUMB:

Gel time calculations can be affectedby measuring devices.

TYPICAL GEL TIMES

Fig 6-4 Using different temperature measuring devices to set the gel plate temperature willresult in different surface temperatures. Gel time will vary depending upon the device

used.

PICK UP TIME

This is the time required for the applied coating to develop sufficient strength to support the

weight of the pipe on the transport wheels without damage to the coating. The elapsed timebetween the last powder gun in the coating booth and the next conveyer wheel is the pick up

time. This time is also known as "time to touch."

Factors in predicting pickup time include gel time, cure time and pipe weight. Gel time alone is

not a good predictor of pickup time. For most currently used systems, the pickup time should be3 5 seconds longer than the gel time. Pipe size and wall thickness affects gel time and cure,therefore a visual inspection is necessary to determine pickup time. Powder manufacturers are a

good source for estimated pickup times.

RULE OF THUMB:

Pickup time should be 3-5 seconds


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after gel time.

Lower Application Temperature

Longer gel time

Longer pick up time

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