Pwht1

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HEAT TREATMENT OF PRESSURE VESSELS

2

HEAT TREATMENT

MECHANICAL PROPERTIES OF METALS & ALLOYS DEPEND ON

CHEMISTRY (ALLOYING ELEMENTS)

&

HEAT TREATMENT

3

WHAT IS HEAT TREATMENT?

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

• HEATING BY VARIOUS SOURCES– HEATING IN A FURNACE – Oil, Gas, Electrical

– HEATING OUT SIDE WITH ELECTRIC HEATING COILS ARROUND THE JOB – Local Heat treatment

– PASSING HOT AIR INSIDE A CLOSSED VESSEL – Internal firing

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HEAT TREATMENT

• HEAT TEATMENT PARAMETERS– RATE OF HEATING

– SOAKING TEMP.

– SOAKING TIME

– COOLING RATE

– COOLING MEDIA

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WHY HT REQUIRED ?

• TO BRING THE PROPERTIES TO THE DESIRED RANGE

–Strength, UTS, YS & Elongation–Toughness–Hardness

• CARRIED OUT IN –FABRICATION INDUSTRIES- Fabricated Components–STEEL PLANTS – Plates, Pipes, Tubes, Sections– FOUNDRY SHOPS - Castings– FORGING SHOPS – Forged Components

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MATERIALS HEAT TREATED

• METALS & ALLOYS – SINGLE PHASE – MULTIPHASE

• ALLOYS– Single Phase : Copper Nickel – Multiphase : Steels

• METALS (Single phase ) – Titanium

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HEAT TREATEMENT

CRITERIA

• COLD WORKED to NORMAL– All materials

• UNEQUILIBRIUM PHASES to EQUILIBRIUM– Stainless Steels ,Maraging Steels

• STRESSED to UNSTRESED– All Materials

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MATERIALS HEAT TREATED

• CS

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

• Stainless Steels

• Non Ferrous Materials

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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

critical temperature followed by cooling in the still air.

To achieve

• Uniform structure

• Change in Mechanical properties,– UTS, YS & Elongation– Hardness – Impact properties

• Refined grains

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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

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SOLUTION ANNEALING

• Austenitic Stainless steels is heated to above 1050°C and held for the desired time followed by fast cooling to room temperature within few minutes by quenching / blowing the air.

Solution annealing is done on stainless steel and non ferrous alloys

• To soften the material

• To remove carbide precipitation formed at grain boundaries during manufacturing process ( SS )

• To improve Corrosion Resistance

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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

• Improves Toughness

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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

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STRESS RELIEVING

The steel is heated to a temperature below 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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STRESS RELIEVING

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

• C - Mn Steels , C - Mo Steels, Cr-Mo Steels – SA 515Gr 70 , SA204GrA, SA387GR11,CL1

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

• Time : 15 minutes min ( 1 hr / inch thick)• Heating Rate : 200° C per hr per inch thick• Cooling Rate : 260° C per hr per inch thick

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

– SA 335P22 ,SA335P5• Temperature : 676° C Min

– Normally 680 - 700° C 2.25Cr– 704 - 720° C 5 Cr

• Time : 15 mts min (1 hr / inch thick)• Heating Rate : 200° C per hr per inch thick• Cooling Rate : 260° C per hr per inch thick

STRESS RELIEVING

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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 (1 hr / inch thick)• Heating Rate : 200° C per hr per inch thick• Cooling Rate : 260° C per hr per inch thick

STRESS RELIEVING

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Steels enhanced by Heat Treatments

• Q&T Steels :– 9.5% Ni Steels , SA 517 Gr E

• Temperature : 538° C Typ– Normally < 600° C

• Time : Min 15 minutes to 2 Hr ( 1 hr / inch thick)• Heating Rate : 200° C per hr per inch thick• Cooling Rate : 260° C per hr per inch thick

STRESS RELIEVING

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LAYOUT OF A TYPICAL FURNACE

(Electrical or Gas fired )

RECORDER P.I.D.

FURNACE

JOB

COMPENSATING CABLE

THERMOCOUPLE

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THERMOCOUPLES

• PRINCIPLE OF A THERMOCOUPLE

• THERMOCOUPLE MATERIAL

• TYPES OF THERMOCOUPLE BEING USED IN HED POWAI / HZW

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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.

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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.

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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.

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TYPES OF THERMOCOUPLE BEING USED IN HZW .

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

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recorder

pid

Compensating cable

Thermocouple wire

Welded junction

CONSTRUCTION OF A

K TYPE THERMOCOUPLE

Accuracy : 0.75%

PROPORTIONAL INTEGRAL

DERIVATIVE

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‘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 %

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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 .

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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)

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RECORDER TYPES OF RECORDER•PAPERLESS -- WITH COLOUR DISPLAY SCREEN ,HARD DISC AND FLOPPY

DRIVE. NOT USED IN HED 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)

•Y-AXIS IS FOR GRAPH SPEED.

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

• GENERALLY KEEP 25 MM / HOUR.

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GRAPH PAPER• GRAPH PAPERS ARE USED FOR PLOTTING THE FURNACE /JOB 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.

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PROCEDURE FOR EMPTY FURNACE CALIBRATION

Calibration of PIDS ( indicator & controller )

1. Connect the millivolt source to the temperatureindicator or controller by a compensating

cable. Care should be taken to clean the wires andterminals thoroughly before connections aremade.

2. The millivolt output for various temperature

ranging from 00C to 10000C in steps of 500C is fedto the indicator / controller.

3. After the millivolt value / temperature readingdisplayed is steady, the reading ofindicator/controller shall be noted.

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Calibration of recorder

1. Connect the millivolt source to the recorder by acompensating cable. Care should be taken toclean the wires and terminals thoroughly beforethe 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.

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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.

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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.

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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.

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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.


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

10000C. ( I. e. 4000C, 4500C, …….., 9500C, 10000C. ) 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 8000C and +/- 100C

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.

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STANDARD OPERATING PRACTICES FOR LOCAL

STRESS RELIEVING

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LOCAL STRESS RELIEVINGWhen

• Local SR to be done only when furnace SR not feasible• Only when certain weld joints on components to be heat

treated

HOW• Done by Electrical heating coil• 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

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LSR -BAND WIDTH

‘X’ = Weld widthX

T

Soak band

Insulation band

Heating band

Insi

de

rad

ius

Lesser of 1T or 2”

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LOCAL STRESS RELIEVING SET UP1. 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.

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LOCAL STRESS RELIEVING

No Welding at top

Multitonne roller

200 to 500mm from heating band

LSR of C/S

SB+HB+IB

Spider orprop

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GOOD ENGG. PRACTICES FOR FURNACE CHARGES

& L S R

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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.

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600mm

900

600mm


450mm

5. Saddle shall be arranged in such away that openend 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)

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SUPPORTING ARRANGEMENTS7. 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

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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.

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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


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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

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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.

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THERMOCOUPLES1. 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.

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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

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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

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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

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THERMOCOUPLES ATTACHMENT UNIT

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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.

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CODE EXTRACTS •FURNACE PWHT• L S R

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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

OPERATION (UCS-68)

• COLD WORKING (UG-79)

• CUSTOMER SPEC.

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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.

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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.

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CODE EXTRACT FOR HEAT TREATMENT( 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.

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CODE EXTRACT FOR HEAT TREATMENT

( 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).

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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.

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( 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.


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SERVICE CONDITION

• LETHAL SERVICE PWHT IS MANDATORY

• EXEMPTIONS ARE FEW


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CODE EXTRACT FOR HEAT TREATMENT( 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”.

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• The temperature of furnace shall not exceed

800’F

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

• Above 8000F( 4270C), the rate of heating shall 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 be a 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.

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CODE EXTRACT FOR HEAT TREATMENT• During the holding period, there shall not be a

greater difference than 1500f ( 830c) 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 ( 4270C), The rate of cooling shall not be

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 ( 2780C Per hour).

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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)

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.

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73

74

75

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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 25014.937.3

SHELL THICKNESS

ISMC 250

DESIGNATION

30.4

125150250250

ISMB 150 8012580

7.67.6

12.514.1

4.44.86.97.1

Annexure-5

77

78

HT REQUEST

79

HT CHARGE

Pwht1

Engineering

c time

c mo steels

cr c mn steels

hr inch thick heating

inch thick cooling rate

crmo steels cr mo steels

stress relieving cmn

cs cmn