PWHT

1

HEAT TREATMENT OF

PRESSURE VESSELS

2

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

3

WHY HT REQUIRED ?

• TO ENHANCE PROPERTIES

–Strength

–Toughness

–Hardness

TO BRING THE PROPERIES SUITABLE FOR FABRICATION

• CARRIED OUT IN

–FABRICATION INDUSTRIES

–STEEL PLANTS

– FOUNDRY

– FORGING SHOPS

4

MATERIALS HEAT TREATED

• METALS & ALLOYS

– SINGLE PHASE

– MULTIPHASE

• ALLOYS

– Single Phase : Copper Nickel

– Multiphase : Steels

• METALS (Single phase )

– Titanium

5

HEAT TREATEMENT

CRITERIA

• COLD WORKED to NORMAL – All materials

• UNEQUILIBRIUM PHASES to

EQUILIBRIUM – Stainless Steels ,Maraging Steels

• STRESSED to UNSTRESED – All Materials

6

MATERIALS HEAT TREATED

• CS

• C-Mn , C-Mo , Cr-Mo , Cr-Mo-V, Ni -Steels

• Stainless Steels

• Non Ferrous Materials

7

TYPES OF HEAT TREATMENT

• NORMALIZING

• ANNEALING

• STRESS RELIEVING

• SOLUTION ANNEALING

• HARDENING

• TEMPERING

• AGEING

8

IRON CARBON DIAGRAM

9

NORMALIZING • The steel is heated to 40° C above the upper

critical temperature followed by cooling in the

still air.

To achieve

• Uniform structure

• Change in Mechanical properties,

– UTS & YS

– Hardness

– Impact properties

• To refine the grains

10

ANNEALING

• Steel is heated 10 to 50°C above the upper critical temperature and held for the desired length of time followed by very slow cooling within the furnace

To achieve:

• Softness & better ductility

• Stresses free material – Stress generated due to mechanical working / previous HT

• Uniform property through out the material

11

SOLUTION ANNEALING

• Austenitic Stainless steels is heated to above

1050°C and held for the desired time followed by

cooling to room temperature within few minutes

by quenching / blowing the air.

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 Resistance

12

AGEING

The Material is heated to a certain temperature,

and held for the desired time; followed by

quenching or cooling in air

Ageing is done on materials susceptible for ageing characteristics : Maraging Steels

• Normally increases strength

• Improve Toughness

13

AGEING

Maraging Steels

M250

• Temperature : 485° C

• Normally 3 Hrs 15 mts

• Heating Rate : 200 C per hr per inch thick

• Cooling Rate : Cool in Air / Quench in water

14

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

15

STRESS RELIEVING

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

• Heating Rate : 200° C per hr per inch thick

• Cooling Rate : 260° C per hr per inch thick

16

Cr-Mo Steels

Cr - Mo Steels (Cr >2%) – SA 335P22 ,SA335P5


– Normally 680 - 700° C 2.25Cr

– 704 - 720° C 5 Cr

• Time : 15 mts min




STRESS RELIEVING

17

Ni -Steels

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


– Normally 600 - 640° C,

• Time : 60 mts min




STRESS RELIEVING

18

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




STRESS RELIEVING

19

LAYOUT OF A TYPICAL

FURNACE

(Electrical or Gas fired )

RECORDER P.I.D.

FURNACE

JOB

COMPENSATING

CABLE

THERMOCOUPLE

20

THERMOCOUPLES

• PRINCIPLE OF A THERMOCOUPLE

• THERMOCOUPLE MATERIAL

• TYPES OF THERMOCOUPLE BEING

USED IN HZW

21

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.

22

THERMOCOUPLE MATERIAL

REQUIREMENT 1. High coefficient of thermal emf.

2. Continuously increasing relation of emf to temperature over

a long range.

3. Freedom from phase changes or other phenomenon giving

rise to discontinuity in temperature emf relationships.

4. Resistance to oxidation, corrosion and contamination.

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.

23

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 converts

the millivolt signal to related temperature.

24

TYPES OF THERMOCOUPLE

BEING USED IN HZW contd... K type :

Dia : 2.5 mm 0. 7 mm

Insulation Bare(ceramic) Refractory

coated

Attachment Mech Capacitor

Usability Reusable Disposable

Location PIT F/c except PIT F/c

Color - Red & Yellow

25

recorder

pid

Compensating

cable

Thermocouple

wire

Welded

junction

CONSTRUCTION OF A

K TYPE THERMOCOUPLE

Accuracy : 0.75%

26

‘S’ TYPE THERMOCOUPLE

• „S‟ TYPE THERMOCOUPLE ARE THE STANDARD

THERMOCOUPLES.

• IT IS USED FOR CALIBRATING “K” Type

THERMOCOUPLES.

• MATERIAL OF CONSTRUCTION

90% PLATINUM + 10% RHODIUM

PLATINUM

• OXIDATION RESISTANCE , SO MORE LIFE .

Accuracy : 0.25 %

27

ISSUE METHODOLOGY For DISPOSAL TYPE

• Users will send their requirement of thermocouple

through Consumable slip ( mentioning HTR No ) to

QA

• QA shall issue the same .

• QA shall issue identification sticker duly attached

• Users shall ensure availability of identification sticker

on unused wire .

28

COMPENSATING CABLE

COMPENSATING CABLE IS DEFINED AS A PAIR OF WIRES

HAVING SUCH EMF TEMPERATURE CHARACTERISTICS

RELATED 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 .

29

P.I.D. PID = PROPORTIONAL INTEGRAL DERIVATIVE

• PID FUNCTIONS BOTH AS PROGRAMMER AND

CONTROLLER • PID CONTROLLER CAN BE ZONE WISE

• PROGRAMME IS MADE IN SEGMENTS AS PER

DIFFERENT STAGES OF HEAT TREATMENT

• DIGITAL DISPLAY IS AVAILABLE FOR PROGRAMME

TEMPERATURE AND FURNACE TEMEPERATURE

• TYPICAL OR REPETITIVE HEAT TREATMENT CYCLE

CAN BE STORED IN PID(PROGRAMMER)

30

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 MFS1 AND 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 TO 1200‟C)

•THE SCALE ON X-AXIS IS NON-LINEAR.

•Y-AXIS IS FOR GRAPH SPEED.

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

• GENERALLY KEEP 25 MM / HOUR.

31

GRAPH PAPER

• GRAPH PAPERS ARE USED FOR PLOTTING THE

FURNACE TEMPERATURE VIA THERMOCOUPLE.

THEY ARE FITTED ON THE RECORDER.

• GRAPH PAPER RECOMMENDED ON RECORDER ONLY

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 PAPER IS

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.

32

STANDARD OPERATING

PROCEDURE FOR HFS-1

FURNACE

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

(BOGIE

WIDTH

)

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

35

STANDARD OPERATING PROCEDURE FOR HFS-1

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 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 furnace charge.

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

36


FURNACE

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 of

inspector on graph paper for firing the furnace.

14. Check LPG level, pressure and temperature in the

storage tanks and note down in logbook.

37


FURNACE

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

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.

38


FURNACE

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 fired

and 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.

39


FURNACE

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.

40


FURNACE

32. Monitor the heat treatment process and graph till

the completion to ensure that it is as per program

and heat treatment request.

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.

41

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.


FURNACE

42

STANDARD OPERATING

PROCEDURE FOR PFS

FURNACE

43

125T Bogie hearth furnace -- PFS

44

BOGGIE WIDTH

4100

2650

5600

10

50

12

35

14

60

5

50

0

BURMER

PFS FURNACE SKETCH

45

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.

46


FURNACE

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.

47


FURNACE

14. Switch on the power supply.

15. Close the bogie door.

16. Switch on ID blower first and then the air blower

and maintain 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).

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.

48


FURNACE

20. Immediately start lighting the pilot burners and adjust

the 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.

49


FURNACE

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.

50

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 and

without marking impression on parent material of

job.

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

the furnace.

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


FURNACE

51

STANDARD OPERATING

PROCEDURE FOR PIT

FURNACE IN MFS-I

52 B

LO

WE

R

3700 1

/D O

F B

AF

FL

E

4150 ( R

EF

RA

CT

OR

Y I/S

)

4961 1000

250 125

1380

4020

TROLLEY

STRUCTURE

CERAMIC

BLANKET

ROOF

BAFFLE

HEATING

ELEMENT CERMIC FIBER

SLABER BLOCK

INSULATING

CASTABLE

FIRE BRICK

OUTER

SHELL

CERMIC

BLANKET

GROUND LEVEL

PIT FURNACE SKETCH

53

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

cable to PID.

54

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 PID‟s prior to starting the furnace.

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‟


FOR PIT FURNACE

55

13. Start recording the time and temperature in the

logbook 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.


FOR PIT FURNACE

56

18. It the job doesn‟t 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.


FOR PIT FURNACE

57

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 1000

0C in steps of 50

0C is fed

to the indicator / controller.

3. After the millivolt value / temperature reading

displayed is steady, the reading of

indicator/controller shall be noted.

58


CALIBRATION

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.

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.

59


CALIBRATION

2. The millivolt output for various temperature

ranging from 400 C to 10000C is fed to the

recorder and is allowed to plot 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.

60


CALIBRATION

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) +/- 10C

6. Recorder +/- on temperature scale.

+/- minutes on time scale.

61

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.

62

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

thermocouples at an interval of 10 minutes.


63


12. The temperature is then raised in steps of 50 C up to

10000C. ( I. e. 400

0C, 450

0C, …….., 950

0C, 1000

0C. ) The

measured temperature is stabilized for 30 minutes.

PID reading are also to be recorded along with this.

13. The allowed temperature variation with respect to the

set temperature is +/- 50C up to 800

0C and +/- 10

0C

above 8000C.

14. This is allowed to plot on the graph and thus

obtained for time and temperature values.

15. Calibration of furnace is valid for 1 year.

64

STANDARD OPERATING

PRACTICES FOR LOCAL

STRESS RELIEVING

65

LOCAL STRESS RELIEVING

WHY • Local SR to be done only when furnace SR not feasible

• When only certain components to be PWHT

HOW • Can be done by Electrical / Gas / diesel / Induction etc..

• DETAILS ON ENSURING PWHT TEMP. IN WELDMENT AREA

• Soaking band(SB) = Widest weld width „x‟+ ‟t‟ or 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

66

LSR -BAND WIDTH

Weld width „X‟ +

lesser of 1T or 2” X

t

Soak band

Insulation band

Heating band

67

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.

68

LOCAL STRESS RELIEVING

No Welding at top

Multitonne roller

200 to 500mm from heating band

LSR of C/S

SB+HB+IB

Spider or

prop

69

GOOD ENGG. PRACTICES

FOR FURNACE CHARGES

& L S R

70

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.

71

600mm

900

600mm


450mm

5. Saddle shall be arranged in such away that open

end of the vessel is maximum 450mm from saddle

support.

6. Saddle shall be located as close to spiders

(temporarily arranged to control deformation) as

possible.

burner

300mm(point no:2)

72


7. Spiders shall be provided as per annexure-5

8 Saddle supports shall be selected as per annexure.-3

9. 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

73

Zero gap

Supporting

arrangement


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.

74

13. Checklist shall be prepared and attached with HT

request 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


75

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 / manways shall be located

towards bottom

76

GENERAL

Temp. support

Furnace floor

Gasket machined surface

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.

77

THERMOCOUPLES

1. All the thermocouples shall be

tagged with aluminum sheet

and identification hard punched

on it.

(For PIT furnace only)

2. Minimum two thermocouples to

be attached for any charge.

78

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

79

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 shall

attach thermocouple

4. A list of qualified person shall be by Welding

Eng.

THERMOCOUPLES

ATTACHMENTS

80

5. Clean surface prior to attachment. 6. Two wire of thermocouple shall be attached one after 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.

THERMOCOUPLES

ATTACHMENTS

81

THERMOCOUPLES

ATTACHMENT UNIT

82

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.

83

CODE EXTRACTS

•FURNACE PWHT

• L S R

84

REQUIREMENT OF HEAT TREATMENT

AS 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

OPERATION (UCS-68)

• COLD WORKING (UG-79)

• CUSTOMER SPEC.

85

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 an

enclosed 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.

86

CODE EXTRACT FOR HEAT TREATMENT

( 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.

87


( 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 true temperature 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 not previously been postweld heat treated.

88


( 8 contd...) The nominal thickness is the total depth of

the weld exclusive of any permitted weld

reinforcement.

For groove weld, the nominal thickness is the

depth of the groove.

For fillet welds, the nominal thickness is the

throat dimension.

If a fillet weld is used in conjunction of groove

weld, the nominal thickness is the depth of the

groove or the throat dimension, Whichever is

greater.

For stud welds, the nominal thickness shall be the

diameter of the stud.

( 9 ) For P–1 material ( carbon steel), minimum holding

temperature during postweld heat treatment shall

be 1100 Deg. F ( 593 Deg.c).

89


P. NO. HOLDING TEMP. NOM.THICKNESS

SOAKING PERIOD

1 ( CARBONSTEEL) & 3(LOW ALLOYSTEEL)

1100 DEG. F(593’C)

UPTO 2” 1 HR. PER INCH. ,HOWEVER 15 MINUTESMINIMUM

OVER 2”TO 5”

2 HOURS , PLUS 15 MIN.FOR EACH ADDITIONALINCH ABOVE 2”

OVER 5 ” 2 HOURS , PLUS 15 MIN.FOR EACH ADDITIONALINCH ABOVE 2”

* POST WELD HEAT TREATMENT IS MANDATORY ON P-NO.3 GR. NO. 3MATERIAL IN ALL THICKNESSES.

90

( 10 ) Postweld heat treatment is mandatory in

Following conditions :

• For welded joints over 1. 5” nominal thickness.

• For welded joints over 1.25” nom. Thickness

through 1.5” nom. Thickness, unless preheat is

applied at a min. Temperature of 200‟F ( 94„c )

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 applying this rule, the

determining thickness shall be the total thickness

of base material.

• When the PWHT is a service requirement.


91

SERVICE CONDITION

• LETHAL SERVICE PWHT IS MANDATORY

• EXEMPTIONS ARE FEW


92


( 11 ) Postweld heat treatment is not mandatory for carbon steel jobs (P1 material ) in Following conditions (UG2):

If groove welds is not over ½” in size or fillet weld with a throat thickness of ½” or less used for attaching non pressure parts to pressure parts provided preheat to a minimum temperature of 200‟F is applied when the thickness of pressure Part exceeds 1.25”. If studs are welded to pressure parts provided preheat to a minimum temperature of 200‟F is applied when the thickness of the pressure parts exceeds 1.25”. for corrosion resistant weld metal overlay cladding or for welds attaching corrosion resistant applied lining provided preheat to a minimum temperature of 200‟f is maintained during application of the first layer when the thickness of the pressure part exceeds 1.25”.

93


• The temperature of furnace shall not exceed 800‟F

( 4270C) at the time when the vessel or part is placed in it.

• Above 8000F( 427

0C), the rate of heating shall not be more

than 4000F Per hour (200

0C/Hour) divided by the maximum

metal thickness of the shell or head plate in inches, but in no

case more than 4000F Per hour( 222

0C Per hour ).

• During the heating period, There shall not be a greater

variation in temperature throughout the portion of the vessel

being heat treated than 2500F( 139

0C) within any 15 feet (

4.6m) interval of length.

94


• During the holding period, there shall not be a

greater difference than 1500f ( 83

0c) between the highest and

the lowest temperature the portion of the vessel being heated

• During the heating & holding periods, the furnace

atmosphere 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.

• Above 8000F ( 427

0C), The rate of cooling shall not be

more than 5000F Per hour (278

0C/Hour) divided by the

maximum metal thickness of the shell or head plate in inches,

but in no case more than 5000F Per hour ( 278

0C Per hour).

95

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. BELOW

MIN. SPECIFIEDTEMPERATURE IN „F

MINIMUM HOLDING

TIME AT DECREASEDTEMPERATURE (NOTE 1)

NOTES

50 (10‟C) 2 HOURS ----

100(38‟C) 4 HOURS ----

150(68‟C) 10 HOURS 2

200(94‟C) 20 HOURS 2

NOTES :1. MINIMUM HOLDING TIME FOR 1” THICKNESS OR LESS ; ADD 15 MINUTES PER INCH OF

THICKNESS FOR THICKNESS GREATER THAN 1”.

2. THESE LOWER POSTWELD HEAT TREATMENT TEMPERATURES PERMITTED ONLY FOR P-NO.1 GROUP NO. 1 AND 2 MATERIALS.

96

97

98

99

100

SELECTION OF SPIDERS AT OPEN ENDS FOR HEAT TREATMENT

10000 10

20

30

40

50

60

70

80

90

100

9500

9000

8500

8000

7500

7000 ISMB 250

6500 ISMB 250 BOX SEC ISMB 250

6000

5500

5000

4500

4000

3500 ISMB 150

3000

2500

2000 ISMB 125 ISMB 150

1500

1000

500 ISMB 125 ISMB 150

10

20

30

40

50

60

70

80

90

100

DATA FOR ABOVE CHANNELS:

WEB HT FLG WD FLG THK WEB THK

SH

EL

L D

IAM

ET

ER

WT/ MTR.(KG)

13

SHELL THICKNESS

ISMB 125 75

ISMB 250

14.9

37.3

SHELL THICKNESS

ISMC 250

DESIGNATION

30.4

125

150

250

250

ISMB 150 80

125

80

7.6

7.6

12.5

14.1

4.4

4.8

6.9

7.1

Annexure-5

101

102

HT REQUEST

103

HT CHARGE

PWHT

Documents

conduct spot

standard operating

postweld heat

spot check

postweld heat

local stress

heat treatment

postweld heat