PHWT Procedure REV (1)

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Project:

Document Title:

POST WELD HEAT TREATMENT
PROCEDURE

Document Issue Record

1 27/03/2021 Revised As Per Comments Farid
0 26/03/2020 Issued for Review
Farid

Rev Issue Date Description Prepared Reviewed Reviewed Endorsed Approved
by by by by by

CONTRACTOR OWNER

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1.0 PURPOSE

This procedure describes the method for conducting Post Weld Heat Treatment
(PWHT) of external Localized electrical resistance in accordance with the
applicable codes and specification.

This procedure applied to PWHT activity related to pipe work, plates, tubes,
headers, flanges, branches & valves for any activity taken by MARK Heat
Treatment.

2.0 APPLICABLE PROCEDURE

This Procedure is written based on applicable working procedure as following
below:

1.0 MHT/SOP/05 : Post Weld Heat Treatment Procedure

3.0 TERMS, ABBREVIATION AND DEFINITION

No TERMS DEFINITION
1 MHT Mark Heat Treatment
2 P.W.H.T Post Weld Heat Treatment
3 WRC Welding Research Council
4 KEV Kapar Energy Ventures

4.0 REFERENCE CODES & STANDARDS

AWS D10.10 - Recommended Practices for Local Heating of
PTS 15.12.01 Welds in Piping and Tubing
Para 6.0 ” Local 360-Degree Band Heating”
Para 8.4 “Location of Thermocouples”
Para 8.4.3“Examples of Thermocouple Locations”

- Welding for Chemical, Oil, and Gas Industries,
February 2016

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WRC BULLETIN 452 Para 9.0 “Post Weld Heat Treatment (PWHT)”
API RP 582 - Recommended practice for local heat of weld in

ASME B31.1 pressure vessel.
- Welding Guideline for the Chemical, Oil, and Gas
ASME VIII DIV. 1
ASME PCC-2 Industries, December 2009
ASME V Para 9.0 “Post Weld Heat Treatment (PWHT)”
- Process Piping, 2007
Para 331.1 “Table 331.1.1 Post Weld Heat
Treatment Requirements”
Para 331.2.6 “Local heat Treatment”
- Rules for Construction of Pressure Vessels, July 2015
UW-40 “Procedures for Post Weld Heat Treatment”
Repair of Pressure Equipment and Piping, 2015
- Non Destructive Examination, 2015
Article 6 – “Liquid Penetrant Examination”
Article 7 – “Magnetic Particle Examination”

5.0 PROCEDURE

5.1 LOCAL P.W.H.T. ( BY RESISTANCE METHOD)

5.1.1 The operation of P.W.H.T. shall be performed in accordance to the
requirement given in the application code and specification section.

5.1.2 The P.W.H.T. shall be conducted in locally by means of electrical
resistance heater.

5.1.3 Minimum requirement for soak band (SB) width, heated band (HB)
width and gradient control band (GCB) width. See Table 1.0 ( Piping)
and 2.0 (Pressure Vessel)

Table 1.0

Summary of Recommendations for the SB, HB, GCB (AWS D10.10)

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Purpose for heating PWHT
Minimum Soak Band (SB) Width
t or 2in. (50mm), whichever is less, on either
side of the weld at its greatest width

Minimum Heated Band (HB) Width SB + 2in. (50mm) or SB + 4√RT

Minimum Gradient Band Control (GCB) Width HB + 4√RT

Reference: AWS D10.10 paras. 6.1.1, 6.2.1 and 6.3.1

Table 2.0

Summary of Recommendations for the SB, HB, GCB (WRC Bulletin 452)

Purpose for heating PWHT

Minimum Soak Band (SB) Width t or 2in. (50mm)

Minimum Heated Band (HB) Width 2√RT + SB

Minimum Gradient Band Control (GCB) Width 4√RT
Reference: WRC Bulletin 452 paras. 5.2.3

5.1.4 Schematic diagram for description of minimum band (SB) width,
heated band (HB) width and gradient control band (GCB) width. See
Figure 1.0

Figure 1.0: Soak band (SB) width, heated band (HB) width and gradient

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control band (GCB) width

5.2 SEQUENCE OF WORK

5.2.1 Thermocouple shall be attached to the center of the weld seam using
a capacitance at prescribed locations as per appendix 1.0.

5.2.2 Perform tack weld on thermocouple at work piece.
5.2.3 Insulation blanket are cut to the size.
5.2.4 Heating elements are placed on the aforementioned backing and

secured with galvanized wires.
5.2.5 Insulation blanket shall be placed on area to be heat treated.
5.2.6 Connecting of heating element
5.2.7 Connecting of thermocouple wire
5.2.8 Test run power supply
5.2.9 Start heating process.
5.2.10 Monitor of Process until finish
5.2.11 Removal of insulation and heating element
5.2.12 Perform DPT after PWHT work completed.
5.2.13 To conduct Hardness Test. See Appendix 4.0

5.3 THERMOCOUPLE LOCATION

5.3.1 The minimum number of thermocouples for pressure vessel should
consider WRC Bulletin 452 and ASME VIII DIV.1. See Table 3.0

a. ASME VIII. DIV. 1 - Thermocouples shall be placed on at the
bottom, centre, and top location.

b. WRC bulletin 452 - Minimum recommended monitoring
thermocouple locations should be considered, especially when
unusual circumstances or uncertainties are present.

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Table 3.0
Comparison of Number Thermocouple Location for PWHT of Pressure Vessel

Code Recommended Number of Control Zones and Thermocouple Location
ASME VIII DIV.1 Three Zones with control thermocouple at top, bottom and center

WRC Bulletin 452 Four Zones (outer surface) with control thermocouple when heating a
cylindrical shell

Two Zone (inner surface) with control thermocouple when heating a
cylindrical shell
Four Zones (outer surface) with control thermocouple when heating a
double curvature shell or head

Two Zone (inner surface) with control thermocouple when heating a
double curvature shell or head

Two Zones (outer surface) with control thermocouple when heating a
nozzle or attachment

one Zone (inner surface) with control thermocouple when heating a
nozzle or attachment
Reference: ASME VIII DIV.1 paras. UW-40 (C) and WRC Bulletin 452 paras. 7.8

5.3.2 Example of thermocouple location as per appendix 1.0

6.0 TEMPERATURE MONITORING

6.1 Temperature shall be monitor using thermocouples and temperature shall
be continuously recorded on the temperature recorder chart.

7.0 TEMPERATURE CONDITION

7.1 Heating from ambient temperature to 200 ⁰C is unrestricted.
7.2 Minimum required soaking temperature and soaking time for PWHT shall be

as per ASME B31.1 Table 331.1.1. Please refer to Appendix 2.0 Table UCS-56
of ASME VIII DIV.1 for Pressure Vessel.
7.3 The cooling rate from control heat temperature to ambient shall not exceed
200 ⁰C / hr.

8.0 HEAT TREATMENT EQUIPMENT

8.1 Temperature recorder

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Temperature recorder shall be Multi- Point temperature indicating recorder –
CHINO 12 pts recorder. The instrument shall be calibrated every 12 months
by third party. Calibration Certificate shall be submitted to client before
commencing work.

8.2 Thermocouple
Chromel – Alumel Thermocouple shall be purchased with certificate of
conformity. It shall be the consumable type 0.8 mm, glass fiber varnish –
finished. Thermocouple shall be attached directly to the metal surface using
a thermocouple welder. This consumable type of thermocouple gives the
greatest accuracy and weld penetration will be only 0.2 mm to 0.3 mm.

8.3 Thermocouple Welder

When the consumable type of thermocouple is to be used for monitoring
temperature, it shall be attached to the metal surface by capacitance
discharged from this instrument.

8.4 Heater

Ceramic Pad Heater (Electrical resistance Heater)

8.5 Power unit
8.5.1 VA Power Transformers.

9.0 REPORTING AND DOCUMENTATION

9.1 The complete temperature cycle of heating, soaking, temperature and
cooling shall be recorded on a chart.

9.2 Temperature measuring devices shall have valid calibration certificates.
9.3 Multi-channel recorder shall be used to measure the temperature of each of

the thermocouple.
9.4 Temperature chart shall be fully identified and with respect to weld joint no,

line, drawing and thermocouple heat treatment arrangement.
9.5 Any discrepancy shall be reported.
9.6 PWHT report(s) and temperature charts shall be furnished to the client site

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Engineer or inspector for approval.

10.0 ATTACHMENTS

Appendix 1.0 – Location of Thermocouple
Appendix 2.0 – Requirement for Post Weld Heat Treatment (for Piping)
Appendix 3.0 – Requirement for Post Weld Treatment (For Pressure Vessel)
Appendix 4.0 – Hardness Test Requirement
Appendix 5.0 – Sketch of Graph

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Appendix 1.0

LOCATION OF THERMOCOUPLE AS PER AWS D10.10

Minimum Number of Thermocouples (Monitoring and Control)
Recommended for Local 360-Degree Band PWHT of a Butt Weld for
Piping in the Horizontal Position with Pipe Size up to 6 NPS (150 DN)

and One Control Zone

Minimum Number of Thermocouples (Monitoring and Control)
Recommended for Local 360-Degree Band PWHT of a Butt Weld for
Piping in the Horizontal Position with Pipe Sizes of 8 and up to 12 NPS

(200 to 300 DN) and Two Control Zones

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Minimum Number of Thermocouples (Monitoring and Control)
Recommended for Local 360-Degree Band PWHT of a Butt Weld for
Piping in the Horizontal Position with Pipe Sizes of 20 and up to 30 NPS

(500 to 750 DN) and Four Control Zones

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Appendix 1.0 (CONT’D)
LOCATION OF THERMOCOUPLE AS PER WRC BULLETIN 452 FOR PRESSURE VESSEL

- Four Zones (outer surface) with control thermocouple when heating a
cylindrical shell

- Two Zone (inner surface) with control thermocouple when heating a
cylindrical shell

- Four Zones (outer surface) with control thermocouple when heating a double curvature shell or head
- Two Zone (inner surface) with control thermocouple when heating a double curvature shell or head

Appendix 1.0 (CONT’D)

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- Two Zones (outer surface) with control thermocouple when heating a nozzle or attachment
- One Zone (inner surface) with control thermocouple when heating a nozzle or attachment

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Appendix 2.0

REQUIREMENT FOR POST WELD HEAT TREATMENT (ASME B31.1)

MARK HEAT TREATMENT

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Appendix 2.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 2.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0
REQUIREMENT FOR POST WELD HEAT TREATMENT (ASME VIII DIV.1)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 3.0 (CONT’D)

MARK HEAT TREATMENT

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Appendix 4.0

HARDNESS TEST REQUIREMENT

S/N MATERIAL, P NO HARDNESS VALUE

1 P-1, P-3 and P-4 225 Brinell

2 P-5B Group 1 241 Brinell

3 P-5A and P-5C Refer to API 934-C

4 P-6 and P-7 (410S) 241 Brinell

5 Ferritic metals in process services, 248 HV10 maximum

including H2 and Sour Service

conditions

6 Ferritic materials in utility service 300 HV10 maximum

(steam, air, water, non-sour service).

7 9 % Ni steels in the as-welded 350 HV10 maximum
condition. 290 HV10 maximum
325 HV10 maximum
8 9Cr-1Mo-V steel (P91, T91) in the PWHT
condition

9 Structural steels.

10 (a) 3.5 % Ni steel, joint thickness ≤ 9.5 250 HV10 maximum
mm (3/8 in). 275 HV10 is permitted in the
(b) 3.5% Ni steel, joint thickness > mid-thickness and cap when
9.5mm (3/8 in) the hardness impression is

located at least 8 mm (5/16 in)

from the internal surface.

Reference: API RP 582 – Para 12.6.2.5 and PTS 15.12.01

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Appendix 5.0 – Sketch of Graph

Temp Deg
C

760 °C Holding Temp = 675-760 °C
Holding Time = 1 hours
Control Heating
Rate 200˚C/h Control Cooling
Rate :200˚C/h

30 deg C Time
(Hour)
1
4 59