heat treatment of pressure vessels

8/13/2019 Heat Treatment of Pressure Vessels

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HEAT TREATMENT OF PRESSURE VESSELS

WHAT IS HEAT TREATMENT?

MATERIALS TREATED BY APPLICATION OF HEAT -NORMALLY DONE IN SOLID STATE

HEATING BY VARIOUS SOURCES PARAMETERS

RATE OF HEATING SOAKING TEMP. SOAKING TIME COOLING RATE COOLING MEDIA

WHY HT REQUIRED ?

CARRIED OUT IN FABRICATION INDUSTRIES

TO ENHANCE PROPERTIES Strength Toughness Hardness

TO BRING THE PROPERIES SUITABLE FOR FABRICATION

STEEL PLANTS FOUNDRY FORGING SHOPS


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MATERIALS HEAT TREATED ?

METALS & ALLOYS SINGLE PHASE MULTIPHASE

ALLOYS Single Phase : Copper Nickel Multiphase : Steels

METALS (Single phase ) Titanium

HEAT TREATEMENT

CRITERIA

COLD WORKED to NORMAL All materials

UNEQUILIBRIUM PHASES to EQUILIBRIUM Stainless Steels ,Maraging Steels

STRESSED to UNSTRESED All Materials

vCS C-Mn , C-Mo , Cr-Mo , Cr-Mo-V, Ni -Steels Stainless Steels Non Ferrous Materials

TYPES OF HEAT TREATMENT NORMALIZING ANNEALING STRESS RELIEVING SOLUTION ANNEALING HARDENING TEMPERING AGEING


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IRON CARBON DIAGRAM


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NORMALIZING

The steel is heated to 40 C above the upper criticaltemperature followed by cooling in the still air.

To achieve

Uniform structure Change in Mechanical properties,

UTS & YS Hardness Impact properties

To refine the grainsANNEALING

Steel is heated 10 to 50C above the upper criticaltemperature and held for the desired length of time followed

by very slow cooling within the furnace

To achieve:

Softness & better ductility Stresses free materialStress generated due to mechanical

working / previous HT

Uniform property through out the materialSOLUTION ANNEALING

Austenitic Stainless steels is heated to above 1050C andheld for the desired time followed by cooling to room

temperature within few minutes by quenching / blowing the

air.


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Solution annealing is done on stainless steel and non ferrous

alloys to achieve following:

To soften the material To remove carbide precipitation formed at grain boundaries

during manufacturing process

To improve Corrosion ResistanceAGEING

The Material is heated to a certain temperature, and held for thedesired time; followed by quenching or cooling in air

Ageing is done on materials susceptible for ageing

characteristics : Maraging Steels

Normally increases strength Improve Toughness

STRESS RELIEVING

The steel is heated to a temperature below or close to the lower

critical temperature with a specific rate of heating. It is held at the

temperature for a desired length of time, followed by cooling with

a specific rate up to certain temperature.

There is no change in grain structure.

Stress relieving is done Fabricated Components of CS & LAS:

To reduce Internal Stresses To soften the steel partially To soften HAZ


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Ni -Steels

Nickel Steels : 1,2,3% Ni SA 203 GrA ,D

Temperature : 593 C Min Normally 600 - 640 C,

Time : 60 mts min Time : 1 hr / inch thick

Heating Rate : 200 C per hr per inch thick Cooling Rate : 260 C per hr per inch thick

Steels enhanced by Heat Treatments

Q&T Steels : 9.5% Ni Steels , SA 517 Gr E Temperature : 538 C Typ Normally < 600 C

Time : Minimum 15 minutes to 2 Hr Time : 1 hr / inch thick


C-Mn , C-Mo , Cr-Mo (< 2% Cr)

C - Mn Steels , C - Mo Steels, Cr-Mo Steels SA 515Gr 70 , SA204GrA, SA387GR11CL1

Temperature : 593 C Min Normally 600 - 640 C, 650-690 C

Time : 15 minutes min Time : 1 hr / inch thick


Cr-Mo SteelsCr - Mo Steels (Cr >2%)

SA 335P22 ,SA335P5


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Temperature : 676 C Min Normally 680 - 700 C 2.25Cr 704 - 720 C 5 Cr

Time : 15 mts min Time : 1 hr / inch thick


THERMOCOUPLES

PRINCIPLE OF A THERMOCOUPLE THERMOCOUPLE MATERIAL TYPES OF THERMOCOUPLE BEING USED IN HZW

PRINCIPLE OF THERMOCOUPLE

The basic principle of thermoelectric thermometry is that a

thermocouple develops an emf which is a function of the

difference in temperature of its measuring junction & reference

junction. If the temperature of reference junction is known, the

temperature of the measuring junction can be determined by

measuring the emf generated in the circuit.

THERMOCOUPLE MATERIAL REQUIREMENT

1.High coefficient of thermal emf.

2.Continuously increasing relation of emf to temperature over along range.3.Freedom from phase changes or other phenomenon giving rise

to discontinuity in temperature emf relationships.

4.Resistance to oxidation, corrosion and contamination.


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5.Homogeneity and reproducibility to fit an establish temperature

& emf relationship.

SPEED OF RESPONSE MAY BE IMPROVED AND

RADIATION & CONDUCTION ERRORS MAY BE REDUCED

BY THE USE OF SMALL DIAMETER THERMOCOUPLES.TYPES OF THERMOCOUPLE BEING USED IN HZW

K type :

Material : Chromel + Alumel

Nickel based ( 10 %Cr ) + ( 2 % Al )Properties : Non-Magnetic + Magnetic

In this type of thermocouple, the wires are joined at one end only

to form a point-type temperature sensor. Instrumentation convertsthe millivolt signal to related temperature.

S TYPE THERMOCOUPLE

S TYPE THERMOCOUPLE ARE THE STANDARDTHERMOCOUPLES.

IT IS USED FOR CALIBRATING K TypeTHERMOCOUPLES.

MATERIAL OF CONSTRUCTION90% PLATINUM + 10% RHODIUM

PLATINUM

OXIDATION RESISTANCE , SO MORE LIFE .ISSUE METHODOLOGY

Users will send their requirement of thermocouplethrough Consumable slip ( mentioning HTR No ) to

QA

QA shall issue the same .


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QA shall issue identification sticker duly attached Users shall ensure availability of identification sticker

on unused wire .

COMPENSATING CABLE

COMPENSATING CABLE IS DEFINED AS A PAIR OF

WIRES

HAVING SUCH EM FTEMPERATURE

CHARACTERISTICSRELATED TO THE THERMOCOUPLE WITH WHICH

THE WIRES ARE INTENDED TO BE USED, THAT

WHEN PROPERLY CONNECTED TO THERMOCOUPLE

THE EFFECTIVE REFERENCE JUNCTION IS IN

EFFECT TRANSFERRED TO THE OTHER END OF THE

WIRES.

MATERIAL ==> +ve COPPER ( white )

-ve COPPER NICKEL (blue ) for K

TYPE .

P.I.D.

PID = PROPORTIONAL INTEGRAL DERIVATIVE

PID FUNCTIONS BOTH AS PROGRAMMER ANDCONTROLLER

PID CONTROLLER CAN BE ZONE WISE PROGRAMME IS MADE IN SEGMENTS AS PERDIFFERENT STAGES OF HEAT TREATMENT


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DIGITAL DISPLAY IS AVAILABLE FORPROGRAMME

TEMPERATURE AND FURNACE TEMEPERATURE

TYPICAL OR REPETITIVE HEAT TREATMENTCYCLE

CAN BE STORED IN PID(PROGRAMMER)

RECORDER

TYPES OF RECORDER

PAPERLESS -- WITH COLOUR DISPLAY SCREEN

,HARD DISC AND FLOPPY DRIVE.NOT USED IN HZW.

WITH PAPER -- CURRENTLY BEING USED IN HZW. 24 CHANNEL -- CURRENTLY BEING USED IN PFS(

CHINO MAKE-- model no.I003

/Graph ET 001).

12 CHANNEL -- CURRENTLY BEING USED IN MFS1AND HFS1

( CHINO MAKE -- model no. EH100 /

Graph ET 201).

COMPENSATING CABLES ARE CONNECTED BEHIND

THE RECORDER SCREEN IN

CHANNELS.

X-AXIS IS FOR TEMPERATURE (RANGE = 0 TO1200C)

THE SCALE ON X-AXIS IS NON-LINEAR. Y-AXIS IS FOR GRAPH SPEED.


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VARIOUS SPEED OF GRAPHS ARE 12.5, 25, 50, 100MM / HOUR

GENERALLY KEEP 25 MM / HOUR.

GRAPH PAPER

GRAPH PAPERS ARE USED FOR PLOTTING THEFURNACE TEMPERATURE VIA THERMOCOUPLE.

THEY ARE FITTED ON THE RECORDER.

GRAPH PAPER RECOMMENDED ON RECORDERONLY

TO BE USED

GRAPH PAPER FOR MFS1 AND HFS1 FURNACE==> ET 201 CHINO MAKE, JAPAN

GRAPH PAPER FOR PFS FURNACE

==> ET 001 CHINO MAKE, JAPAN

THE LENGTH OF ONE BUNDLE OF GRAPH PAPERIS

GENERALLY 2000 MM.

DOTTING TYPE RECORDER INK (CHINO MAKE,JAPAN)

IS USED IN RECORDER FOR PLOTTING OF GRAPH.

USUALLY , 6 COLOURS ARE FILLED FOR PLOTTING.

STANDARD OPERATING

PROCEDURE FOR HFS-1 FURNACE


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33

1650

3575

14300.

3575 3575 3575

( ZONE-1 ) ( ZONE-3 ) ( ZONE-5 ) ( ZONE-7 )

( ZONE-2 ) ( ZONE-4 ) ( ZONE-6 ) ( ZONE-8 )

1640 1650

7900

(BOGIEW IDTH

)

BURNER

HFS-I FURNACE SKETCH

34

7900 BOGGIE WIDTH

8700

1050

9500

9000

1195

1. PROJECT NO:

2. SECTION NO :

3. CHARGE NO :

4. H. T. REQ. NO :

BURNER

HFS-I FURNACE SKETCH


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STANDARD OPERATING PROCEDURE FOR HFS-1

FURNACE

Receive the job as per HT request.

2. Receive heat treatment request duly approved by metallurgy engineer.

3. Ensure that Insp. Clearance is available prior

to loading for job.

4. Load the supporting arrangement as per the attached

annexure -3

5. Ensure the spider arrangement as per attached

annexure - 5

6. Fix the thermocouples at locations shown in furnacecharge.

7. Check the entire job as per check list (annex.-I).

9. Move the bogie inside the furnace

10. Pass the thermocouples through ports and

connect it with compensating cables

11. Set the program as per heat treatment request. Secure it

and then run it in fast mode as check. Bring it back to the

initial segment and hold.

12. Insert heat treatment chart in recorder and adjust the

speed of the graph.

13. Clear inspection of job and get the signature ofinspector

on graph paper for firing the furnace.

14. Check LPG level, pressure and temperature in the

storage tanks and note down in logbook.

15. Switch on the power supply

16. Close the bogie door

17. Follow the procedure for startup of furnace in zone-I

18. Start the blower from the field push button station

provided

19. Give power supply to the ignition panel

20 When the system healthy contact comes from the


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instrument panel, the lamp for the system healthy

signal is on. This indicates that the combustion air

pressure and gas pressure are within the specified

limits

21. Now the firing on the cycle can start.22. Open the pilot and main gas valves

23. Press start cycle button on doing so the cycle starts

and purging start indicator lamp is on.

24. After 3 minutes ( time adjusted through timer ) the

purging is completed and ignition start lamp is ON

At the same time the purging start lamp gets OFF.

25. After 10 seconds the ignition start lamp gets OFF

By this time the pilot burner should have been firedand the pilot flame is established.

26. Flame healthy signal LED gets on which is provided

on the flame sensor relay. This can be viewed through

the glass window provided in the ignition panel.

27. Due to certain length of pipe between the burner and

solenoid valves, which may contain air, the burner

may not light up in the first attempt. In that case,

repeat the above mentioned procedure.

28. Once the main flame is established, the control is

passed on to the temperature controller.

29. For startup of furnace in other zones, follow the same

steps no 16 to 27 mentioned above.

30. After all zones are started, start recording time and

temperature from recorder every 30 minutes in the

logbook.

31. Conduct spot checks for heat treatment every 4hours

and fill the spot check format.32. Monitor the heat treatment process and graph till the

completion to ensure that it is as per program and heat

treatment request.


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33. After heat treatment cycle is completed, shut off all

LPG supply valves and let furnace run with blowers on for

15 minutes.

34. Open the bogie door. Disconnect thermocouples from

compensating cable.35. Submit the graph and duly filled spot check formats to

inspection for approval of heat treatment.

36. Retrieve the thermocouples from the ports and the

bogie out of the furnace.

37. Allow the job to reach room temperature.

38. Remove the thermocouples from the job carefully

without damaging the junction of thermocouples and

without making impression on parent material of job.39. Unload the job from the bogie and move the bogie

inside the furnace.

40. Close the furnace. Shut off the main power supply.

43

125T Bogie hearth furnace -- PFS


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STANDARD OPERATING PROCEDURE FOR PFS

FURNACE

1. Receive the job as per HT request.2. Receive heat treatment request duly approved by

metallurgy engineer.

3. Ensure that Insp. clearance is available prior to

loading for job.

4. Load the job on the bogie as per the heat treatment

furnace request.

5. Ensure the supporting arrangement as per the

attached annexure-I.6. Ensure the spider arrangement as per annexure- II.

7. Fix the thermocouples at locations shown in furnace

charge.

8. Check the entire job as per check list attached as

annexure-III

9. Move the bogie inside the furnace.

10. Pass the thermocouples through ports and

connect it with compensating cables.

11. Insert heat treatment chart in recorder and adjust the

speed of the graph.

12. Clear inspection of job and get the signature of

inspector on graph paper for firing the furnace.

13. Check LPG level, pressure and temperature in the

storage tanks and note down in logbook.

14. Switch on the power supply.

15. Close the bogie door.

16. Switch on ID blower first and then the air blower andmaintain pressure at about 800mm WG by slowly opening

the suction valve.

17. Ensure that pressure of LPG from yard to inlet of

pressure regulator is always less than 20psi (1.5kg/CM2).


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18. Open the inlet valve to the regulator and open the

outlet valve.

19. If pressure exceeds 1600 mm WG , isolate the

pressure by lifting the handle of safety shut off valve.

20. Immediately start lighting the pilot burners and adjustthe flame with the air valve .

21. Open the isolating valve for pressure gauge and

adjust the pressure regulator by turning the screw

provided in the stem so that the pressure is

maintained at about 1000mm WG.

22. Light up alternate main burners and adjust the flame

lengths uniformly.

23. Lock the doors by pneumatic locking.24. After all zones start, record time and temperature

from recorder every 30 minutes in the logbook.

25. Conduct spot checks for heat treatment every 4

hours and fill the spot check format. Monitor the heat

treatment process and graph per heat treatment

request.

26. After the heat treatment cycle is completed, shut off all

LPG valves and let furnace run with blowers on for 15

minutes.

27. Open the bogie door. Disconnect thermocouples from

compensating cables.

28. Submit the graph and duly filled spot check formats to

inspection for approval of heat treatment.

29. Retrieve the thermocouples from the ports and move

the bogie out of the furnace.

30. Allow the job to reach room temperature.

31. Remove the thermocouples from job carefully andwithout marking impression on parent material of

job.

32. Unload the job from bogie and move the bogie insidethe

furnace.

33. Close the furnace. Shut off the power supply.


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52

BLOWER

37001/DOFBAFFLE

4150(REFRACTORYI/S

)

49611000

250125

1380

4020

TROLLEYSTRUCTURE

CERAMIC

BLANKET

ROOF

BAFFLE

HEATINGELEMENT

CERMIC FIBERSLABER BLOCK

INSULATING

CAST ABLE

FIRE BRICKOUTERSHELL

CERMICBLANKET

GROUND LEVEL

PIT FURNACE SKETCH

STANDARD OPERATING PROCEDURE

FOR PIT FURNACE

1. Receive heat treatment request duly authorized by

metallurgy engineer.2. Receive the job for heat treatment with

inspection clearance.

3. Put the job either on support or on heat

treatment fixture inside the furnace.

4. Ensure that equal clearance is available on all sides

between job and baffle.

5. Ensure that the furnace is calibrated.

6. Connect thermocouples with compensating cableto PID.

7. Set the program in the programmer as per heat

treatment request.

8. Take a trial run of program to ensure the accuracy.

9. Calibrate all 5 PIDs prior to starting the furnace.


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10. Insert the graph inside the recorder and take the

signature of inspector on the graph paper.

11. Close the furnace door.

12. Start the furnace by giving power supply ON

13. Start recording the time and temperature in thelogbook every 30 minutes.

14. Ensure that the cycle is functioning as per program.

15. After the heat treatment is over, open the furnace

cover.

16. If the job calls for water quenching, lift the job and

dip it in quench tank.

17. It the job calls for air cooling in still air, lift the job

and put it outside on supports in open air.18. It the job doesnt call for anything above, allow the job

to cool down in furnace.

19. Keep the job outside after removing from furnace.

20. Submit the heat treatment graph to inspection for

approval of heat treatment cycle.

21. Close the furnace cover after the furnace is cooled

down to room temperature.

PROCEDURE FOR EMPTY FURNACE CALIBRATION

Calibration of PIDS ( indicator & controller )

1. Connect the millivolt source to the temperature

indicator or controller by a compensating cable. Care

should be taken to clean the wires and terminals

thoroughly before connections are made.

2. The millivolt output for various temperature

ranging from 00C to 10000C in steps of 500C is fed tothe indicator / controller.

3. After the millivolt value / temperature reading

displayed is steady, the reading of

indicator/controller shall be noted.


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4. If the error in the indicated readings is more than the

specified accuracy ( +/- 10C ), then correction to be carried

out for the indicator / controller and points 1 to 4 shall be

repeated till the specified accuracy is obtained is obtained.

Calibration of recorder

1. Connect the millivolt source to the recorder by a

compensating cable. Care should be taken to clean the

wires and terminals thoroughly before the connections are

made.

2. The millivolt output for various temperature ranging

from 400 C to 10000C is fed to the recorder and is allowed toplot on a graph.

3. The graph thus obtained is reviewed for time and

temperature values. These values should meet the accuracy

requirements.

4. If there is error in the values plotted on the graph,

then correction to be carried out for the recorder and points 1

to 4 shall be repeated till the specified accuracy is

obtained.

EQUIPMENT REQUIRED ACCURACY

1. 20 Nos. big K-type thermocouples +/- 0.25%

2. 10 Nos. small K-type thermocouples +/- 0.25%

3. Millivolt source (wahl unit )

( 1 micro volt at 1000 micro volts )

4. Heat treatment fixture.

5. Temperature indicators (PID) +/- 10C6. Recorder +/- on temperature scale.

+/- minutes on time scale.


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PIT FURNACE CALIBRATION PROCEDURE

1. Ensure that the PIDs are calibrated as mentioned above.

2. Ensure that the recorder is calibrated as mentioned above.

3. Ensure that all the thermocouples used are calibrated.

4. Ensure that the thermocouples are attached to the heat

treatment fixture as shown in sketch-I.

5. Place the heat treatment fixture inside the furnace with

thermocouples in position.

6. Close the furnace lid. Start the furnace and the recorder.

7. Set the temperature of controller to 4000C.8. After reaching the set temperature, it is allowed to

stabilize for half an hour.

9. Measure and record the temperature indicated by

each of the 20 thermocouples. The temperature is to be

read through WAHL UNIT.

10. Three sets of readings are to be taken for each

thermocouples at an interval of 10 minutes.

11. Also record the readings indicated by each of the


7. Set the temperature of controller to 4000C.

8. After reaching the set temperature, it is allowed to

stabilize for half an hour.

9. Measure and record the temperature indicated by

each of the 20 thermocouples. The temperature is to be

read through WAHL UNIT.

10. Three sets of readings are to be taken for each

thermocouples at an interval of 10 minutes.11. Also record the readings indicated by each of the



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STANDARD OPERATING

PRACTICES FOR LOCAL STRESS RELIEVING

LOCAL STRESS RELIEVING

WHY?

Local SR to be done only when furnace SR notfeasible

When only certain components to be PWHTHOW?

Can be done by Electrical / Gas / diesel /Induction etc.. DETAILS ON ENSURING PWHT TEMP. IN

WELDMENT AREA

Soaking band(SB) = Widest weld width x+ tor 2 inches

whichever is less from edge of weld

Heating band width (HB) Induction stress level Through thickness criteria SB + 4 rt where r = Inside radius, t =

thickness

Insulation band width (IB) Axial gradient HB + 4 rt


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LOCAL STRESS RELIEVING SET UP

1. Provide multitonne roller on one end of vessel during

LSR of circular seam when job is horizontal.2. If both ends are open during LSR, provide insulation

from inside. If not possible , prevent airflow so that

temperature on inside surface do not drop down.

3. Spider/prop shall be provided in such a way that upper

portion of spider / prop is not welded with inside

surface to allow contraction/expansion of shell surface.

4. Spider/prop shall be between 200- 500mm from heating

zone.5. Temporary attachments, provided for holding insulation,

shall be within soak band only.

6. Minimum two thermocouples shall be provided from

inside, when accessible.

GOOD ENGG. PRACTICES

FOR FURNACE CHARGES

& L S R

SUPPORTING ARRANGEMENTS

1. Minimum distance between wall of furnace and the

job shall be 600mm.

2. Minimum distance between floor of the furnace and

lower most part of the job shall be 300mm.

3. The distance between the flame of burner and saddle

support shall be 600mm.4. Minimum 90 degree saddle to be used, however 120

degree saddle is desirable.

5. Saddle shall be arranged in such away that open end

of the vessel is maximum 450mm from saddle support.


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6. Saddle shall be located as close to spiders

(temporarily arranged to control deformation) as

possible.

7. Spiders shall be provided as per annexure-5

8 Saddle supports shall be selected as per annexure.-39. Spiders or vertical prop shall be provided at open

ends, center and below man way/nozzles above 24 10.

Avoid gap between saddle support and job surface

11. Locking/clamping of job, restricting the movement

(axial/lateral) during heat treatment shall be avoided.

12. All long nozzles projecting outside job surface shall

be supported

13. Checklist shall be prepared and attached with HTrequest before furnace is fired as per Ann-1

14. Spot check report shall be filled by supervisor as per

Annexure-2 during job is being heat treated.

15. Moonplate support and welding inside surface prior

to release for Heat treatment as per

Annexure-4

16. General idea about thermocouple locations and its

attachments is as per Annexure-6

GENERAL

1. Blocking the flame of the burner is not desirable

2. Burner shall have blue flame and not yellow

3. Flame shall not directly impinge on job

4. All burners shall be fired at a time

5. Keep all job nozzles open during heat treatment

6. Above 24 nozzles / manwaysshall be located towardsbottom

7. Deoxidization agent shall be applied on all

machined and gasket faces

8. Gasket / machined face of loose assemblies shall not

be touching any object.


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THERMOCOUPLES

1. All the thermocouples shall be

tagged with aluminum sheetand identification hard punched

on it.

(For PIT furnace only)

2. Minimum two thermocouples to

be attached for any charge.

3. Minimum 8 thermocouples to be used for a charge in

HFS- I furnace if the job occupies all 8 zones

4. Maximum distance between two thermocouples for a

sample job is as shown in annexure- 6

5. PTC shall have separate thermocouple

THERMOCOUPLES ATTACHMENTS

1. Use only TAU-90 capacitor Discharge Welding machine

for thermocouple connection

2. Use WPS:999-154 R0 for attachment of

thermocouple for cs/alloy steel material

3. Only trained person by welding engineering shallattach thermocouple

4. A list of qualified person shall be by Welding

Eng.


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5. Clean surface prior to attachment.

6. Two wire of thermocouple shall be attached oneafter another.

7. Gap between two wire of a thermocouple shall be

max. 3.0mm

8. Only calibrated thermocouple shall be used.

Calibration shall be by QA.

9. After PWHT, thermocouple area shall be ground

and DP shall be carried out.

SPECIAL NOTE

IF THE TEMPERATURE OF HEAT TREATMENT

EXCEEEDS 650-DEGREE CENTIGRADE, THE

MATERIAL AND SIZE OF SPIDERS AND SUPPORTS TO

BE DECIDED BY PLANNING AND APPROVED BY

DESIGN.

REQUIREMENT OF HEAT TREATMENTAS PER ASME-SEC VIII Div.-1

SERVICE CONDITION (UW-2) MATERIAL (UG-85, UW-40,UCS-

56,UAT-80,UHA-32,UNF-79)

THICKNESS (UG-85, UW-40,UCS-56,UAT-80,UHA-32,UNF-79)

LOW TEMERATURE


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OPERATION (UCS-68)

COLD WORKING (UG-79) CUSTOMER SPEC.

CODE EXTRACT FOR HEAT TREATMENT

( 1 ) The soak band shall contain the weld, heat affected zone

and a portion of base metal adjacent to the weld being heat

treated. The minimum width of this volume is the widest

width of weld plus 1T or 2 inches, whichever is less, on each

side or end of the weld. The term T is the nominal thickness.

( 2 ) The operation of postweld heat treatment shall be

performed either by heating the vessel as a whole in anenclosed furnace or heating the vessel in more than one heat in

a furnace, provided the overlap of the heated sections of the

vessel is at least 5 feet ( 1.5m). When this procedure is used,

the portion outside of the furnace shall be shielded so that the

temperature gradient is not harmful. The cross section where

the vessel projects from the furnace shall not intersect a nozzle

or other structural discontinuity.

( 3 ) When the vessel is required to be postweld heat treated,

and it is not practicable to postweld heat treat the completed

vessel as a whole or in two or more heats; any circumferential

joints not provisionally heat treated may be thereafter locally

postweld heat treated by heating such joints by any

appropriate means that will assure the required uniformity.

( 4 ) While carrying out local postweld heat treatment, the

soak band shall extend around the full circumference. The

portion outside the soak band shall be protected so that the

temperature gradient is not harmful.( 5 ) Heating a circumferential band containing nozzles or

other welded attachments in such a manner that the entire

band shall be brought up uniformly to the required

temperature and held for the specified time.


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( 6 ) Where more than one pressure vessel or more pressure

vessel part are postweld heat treated in one furnace charge,

thermocouples shall be placed on vessels at the bottom, center,

and top of the charge or in other zones of possible temperature

variation so that the temperature indicated shall be truetemperature for all vessels or parts in those zones.

( 7 ) Postweld heat treatment, When required, shall be done

before the hydrostatic test and after any welded repairs. A

preliminary hydrostatic test to reveal leaks prior to PWHT is

permissible.

( 8 ) For pressure vessels or parts of pressure vessels being

post weld heat treated in a furnace charge, it is the greatest

weld thickness in any vessel or vessel part which has notpreviously been postweld heat treated.

The nominal thickness is the total depth of the weld

exclusive of any permitted weld reinforcement.

For groove weld, the nominal thickness isthe depth of the groove.

For fillet welds, the nominal thickness isthe throat dimension.

If a fillet weld is used in conjunction ofgroove weld, the nominal thickness is thedepth of the groove or the throat dimension,

Whichever is greater.

For stud welds, the nominal thicknessshall be the diameter of the stud.

( 9 ) For P1 material ( carbon steel), minimum holding

temperature during postweld heat treatment shall be

1100 Deg. F ( 593 Deg.c).

10 ) Postweld heat treatment is mandatory in Following

conditions :

For welded joints over 1. 5 nominalthickness.


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For welded joints over 1.25 nom.Thickness through 1.5 nom.

Thickness, unless preheat is applied at

a min. Temperature of 200F ( 94c )

during welding. Vessels or parts of vessels

constructed of base material with

corrosion resistant integral or weld

metal overlay cladding or applied

corrosion resistant lining material

shall be postweld heat treated when

the base material is required to be

postweld heat treated. In applyingthis rule, the determining thickness

shall be the total thickness of base

material.

When the PWHT is a servicerequirement.

SERVICE CONDITION

LETHAL SERVICE PWHT ISMANDATORY

EXEMPTIONS ARE FEW( 11 ) Postweld heat treatment is not mandatory for carbon

steel jobs (P1 material ) in Following conditions (UG2):

If groove welds is not over insize or fillet weld with a throat

thickness of or less used for

attaching non pressure parts to

pressure parts provided preheat to

a minimum temperature of 200F is

applied when the thickness of

pressure Part exceeds 1.25.

If studs are welded to pressureparts provided preheat to a


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minimum temperature of 200F is

applied when the thickness of the

pressure parts exceeds 1.25.

for corrosion resistant weldmetal overlay cladding or forwelds attaching corrosion resistant

applied lining provided preheat to

a minimum temperature of 200f is

maintained during application of

the first layer when the thickness

of the pressure part exceeds

1.25.

The temperature of furnace shall notexceed 800F( 4270C) at the time when the vessel or part is placed in it.

Above 8000F( 4270C), the rate of heatingshall not be more than 4000F Per hour

(2000C/Hour) divided by the maximum metal

thickness of the shell or head plate in inches,

but in no case more than 4000F Per hour(

2220C Per hour ). During the heating period, There shall not bea greater variation in temperature throughout

the portion of the vessel being heat treated

than 2500F( 1390C) within any 15 feet ( 4.6m)

interval of length.

During the holding period, there shall not be agreater difference than 1500f ( 830c) between the highest

and the lowest temperature the portion of the vessel being

heated

During the heating & holding periods, the furnaceatmosphere shall be so controlled as to avoid excessive

oxidation of the surface of the vessel. The furnace shall be

of such design as to prevent direct heat impingement of

the flame on the vessel.


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Above 8000F ( 4270C), The rate of cooling shall notbe more than 5000F Per hour (2780C/Hour) divided by

the maximum metal thickness of the shell or head plate in

inches, but in no case more than 5000F Per hour ( 27 80C

Per hour).when it is impractical to postweld heat treat at the temperature

specified in table mentioned in Sr.. No. 9, It is permissible to

carry out the post weld heat treatments at lower temperatures

for longer periods of time as shown in table below

DECREASE IN TEMP. BELOWMIN. SPECIFIED

TEMPERATURE IN F

MINIMUM HOLDINGTIME AT DECREASED

TEMPERATURE (NOTE 1)

NOTE

50 (10C) 2 HOURS ----

100(38C) 4 HOURS ----

150(68C) 10 HOURS 2

200(94C) 20 HOURS 2

heat treatment of pressure vessels

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