Pwht Procedure

AMIGOS TECHNICAL SERVICES ( S ) PTE LTD POST WELD HEAT TREATMENT PROCEDURE

Doc No

: ATS-PWHT-001

Revision No : 01 Date

:

POST WELD HEAT TREATMENT PROCEDURE

DESCRIPTION

NAME

SIGNATURE

PREPARED BY

REVIEWD BY

APPROVED BY

REVISION STATUS

S.NO

REVISION No.

DATE

DESCRIPTION

Page 1 of 11


Doc No

: ATS-PWHT-001


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CONTENTS Page 1.

Scope……………………………………………………………………………

3

2.

Heating Item / Work Volume, Location, Schedule………………………….

3

3.

Applicable Code & Specification……………………………………………..

3

4.

Heat Treatment ( PWHT ) Method……………………………………………

3–4

5.

Temperature Monitoring……………………………………………………….

4

6.

Precautions……………………………………………………………………..

4

7.

Important Measures During PWHT……………………………………….....

5

8.

Temperature Ranges....………………………………………………………

5

9.

Temperature Control System…………………………………………………

6

10.

Personnel‟s Qualification……………………………………………………..

6

11.

Report / Documentation………………………………………………………

6

12.

Heat Treatment Equipment………………………………………………….

7

Appendix 1

Sketch : Width of Heated & Insulted Zone ( LOCAL PWHT )

Appendix 2

Thermocouple Locations ( LOCAL PWHT )

Attachments

:

PWHT Report Form

( Specimen )

Page 2 of 11


Doc No


1.

: ATS-PWHT-001

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Scope This document covers the procedure for PWHT Work of High Pressure Piping system Weld joints by localized heating method for carbon and manganese steel, alloy steel materials and castings.

2.

HEATING ITEM / WORK VOLUME, LOCATION, SCHEDULE

HEATING ITEM Various sizes of piping welds range from Ø0.75” ~ Ø16” Thickness range : Less than 50.8mm Also structural weld joints of varying thickness

3.

APPLICABLE CODE & SPECIFICATION 1. 2. 3. 4. 5.

4.

ASME code Section VIII Div.1 2001 ED , chapter UCS-56 ASME B31.3 DNV-OS-C101 or DNV-OS-C201 AWS D1.1 Client‟s Specification

HEAT TREATMENT ( PWHT ) METHOD 4–1

Weld Joints shall be locally heat-treated in such manner that the entire Band be brought up uniformly to the required temperature and held for the specified period of time, in accordance with the codes specifications stated in the above section 3.

4–2

Minimum Required Heated Band Width: 1.

In Local PWHT of Butt Weld Joint, the minimum width of the Circumferential Heat Band, measured from CENTRE of the Weld, shall extend 2.5ѵRT beyond the edge of the weld. ( R = inside Diameter in mm ; T = pipe wall thickness in mm )

2.

3.

In Local PWHT of welded Branch Connection, the minimum Width of the heated band shall extend at least 2.5ѵRT beyond The edge of the weld joining the branch or attachment to the run pipe. In local PWHT of Bend or formed sections, the minimum width Of the heated band shall extend to 2.5ѵRT on each side of the Bent or formed area.

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4.

: ATS-PWHT-001

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HEAT TREATMENT ( PWHT ) METHOD – CON’T

4–3

Thermal Insulation: (a) The insulation width, measured from the center of the weld, Shall extend at least 5ѵRT beyond the edge of the weld. (b) Density of 128Kg/m3 Ceramic fiber insulation blanket shall be Used the thermal insulation. (c) The insulation blanket will be kept in position with iron or steel Wire. (d) Wherever possible, the ends of piping should be sealed to Prevent internal air currents from creating excessively high Thermal gradients through the thickness of the piping. (e) After heat treatment , all materials shall be cooled in still air, Protected from rain and draught.

4–4

Thermocouple Location: (a) Thermocouple shall be firmly attached to the center of the Weld zone using a capacitance-discharge type thermocouple Welder. A demonstration will be carried out upon client‟s Request. (b) When tack welding thermocouple onto the work piece, Precautions shall be taken so as not to create defects such as Undercuts, arc strike, etc and the welded zone shall be Smoothly finished by grinder after heat treatment. (c) All thermocouple attachments shall be adequately insulated by High temperature misreading caused by the effect of radiation. (d) The miminum number/location of the thermocouple to be Attached to the work place shall be as follows:

Weld sizes ( NPS )

No.of T/C

(a) D≥6”

1 no

(b) 6”
2 no

(c) D≥ 16”

3 or more

Locations 9 O‟clock ( center )

1800 apart ( top & bottom )

Every 600mm from each other, or in ¼ of the outer Circumference, whichever Distance is the smallest. (pls refer to APPENDIX-2)

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4-4-1

: ATS-PWHT-001

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For Structural Joints :

Thermocouple can be placed as per the clients requirement or at a Regular intervals of 0.5m whichever is suitable

5.

TEMPERATURE MONITORING 5–1

6.

7.

Temperature monitoring shall be done by the thermocouples and Temperature shall be recorded continuously on temperature record Chart.

PRECAUTIONS

6–1

It is vital to highlight the need for adequate support of work piece Prior to commencing any heat treatment to minimize possible Misalignment, distortion, collapse or deformation.

6–2

Exposed, machined and threaded surface shall be protected from Oxidation by applying Anti-Seize and Lubricating Compound prior to PWHT.

IMPORTANT MEASURES DURING PWHT

Upon the occurrence of below-mentioned problems during LOCAL PWHT Operation, the following should be observed:

FAULT / PROBLEM

RAIN

ACTION NOT ALLOWED

CORRECTIVE ACTION

No weather protection Provided before heating

Provide proper and Adequate weather Protection before heating

Page 5 0f 11


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8.

: ATS-PWHT-001

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TEMPERATURE RANGES :

The procedure for PWHT has to be followed for the various steel grades as mentioned below.

Material Grade

Temperature Range

Heating / Soaking TIme

Rate of Heating

Rate of Cooling

Alloy Steels ASTM A 335 P4

705° - 749°

2 Hrs / 25mm wall Thickness soaking 2 hrs minimum

100°C / Hrs / 25mm wall thickness


705° - 760°




705° - 749°




730° - 790°




590° - 650°





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: ATS-PWHT-001


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Page 6 of 11

9.

TEMPERATURE CONTROL SYSTEM Temperature will be controlled by combination of program setter (1) which Generates voltage (mv) equivalent to the electromotive force of “k” Thermocouple with temperature controller (2), and the Heater (4) will be Controlled by the difference of thermal electromotive force of thermocouple (5).

Schematic Sketch of Heat Treatment process

Workpiece Power Source

„k‟ type mV Program Setter (1)

Temperature Controllerpulse (2)

On/off pulse

Power Regulator (3)

Heater (4)

Temperature Recorder

10.

PERSONNEL’S QUALIFICATION Heat Treatment operator shall have at least one year of field experience in the Heat treatment work described in this Procedure.

+


Doc No

: ATS-PWHT-001


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Page 7 of 11

11.

12.

REPORT / DOCUMENTATION

11 – 1

A Time-Temperature Record Chart shall be provided for each heat Treatment operation. Each chart is to show: (a) Item Identification Number ( Job, Unit, System, ISO, Tag/Piece No.etc (b) Number of Thermocouples (c) Time and Date Started (d) Chart Speed ( inches/hr) (e) Heating / cooling Rates, Soak Temperature & Soak Time (f) Model & serial number of temperature recorder , including date of calibration (g) Name of operator (h) The Approval signature of Client‟s site representive

11 – 2

A copy of Thermocouple Certificate provided by the supplier and Calibration Certificate of Temperature Recorder will be attached Together with the heat treatment Report and temperature chart.

HEAT TREATMENT EQUIPMENT’S

12 – 1

Temperature Recorder It is Chino 12pts recorder calibrated for type “k” chromel / alumel Temperatures. The instrument shall be calibrated every 12 months by a third party. Calibration Certificate shall be submitted to Clients before commencing Work.

12 – 2

Program Controller It consists of Chino Program Setter and Chino Temperature Controller.

12 – 3

Thermocouple It shall be Chromel-Alumel type “k” thermocouple (consumable type, 0.8mmØ, glass fiber varnish finished) for temperature range up to 900°C. Thermocouple will be attached directly onto metal surface of the work piece Using a thermocouple Welder. This consumable type of thermocouple gives The greatest accuracy and weld penetration will be only 0.2mm to 0.3mm.


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: ATS-PWHT-001


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Page 8 of 11

12 – 4

Thermocouple Welding Unit When counsumable type of thermocouple is to used for monitoring Temperature, it will be attached to the metal surface by capacitance Discharge from this instrument.

12 – 5

Thermocouple Compensating Lead It shall be Copper / Constantan when used in conjunction with type “k” Thermocouple.

12 – 6

Electric Resistance Heater 2.7Kw Ceramic Pad Heaters.

12 – 7

Power Regulator 60Kva Step down Transformer c/w built in ELCB x 6 channels 60 Kva output

12 – 8

High Temperature Ceramic Putty This is used to insulate the hot junction of thermocouple, so as to avoid Temperature misreading caused by the effect radiation.

12 – 9

Insulation Blanket Density of 128Kg/m3 ceramic fiber blanket Size: 7200L x 600W x 25T (mm) per roll Maximum services temperature: 1200°C

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: ATS-PWHT-001


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Page 9 of 11

APPENDIX – 1

WIDTH OF HEATED & INSULATED ZONES ( FOR LOCAL PWHT )

Heated Band Width Weld Centre Line

2.5ѵRT

Heating Element

2.5ѵRT

Insulation

5ѵRT

5ѵRT

Insulation Width

Where R = Inside Diameter in mm, T = Pipe Wall thickness in mm.


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: ATS-PWHT-001


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Page 10 of 11 APPENDIX – 2

THERMOCOUPLE LOCATIONS ( LOCAL PWHT )

All thermocouples are to be attached on the center of the weld. 1) D ≤ 6”

: 1 thermocouple – 9 O‟ clock ( CENTRE)

2) 6” < D < 16”

: 2 thermocouple ( TOP & BOTTOM )

3) D ≥ 16”

: 3 or more thermocouples ( Every 600mm from each other or in ¼ of The outer circumference, whichever Distance is the smallest )

600mm

600mm


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: ATS-PWHT-001


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Page 11 of 11

Pwht Procedure

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