pwht procedure for petrol steel _ core

1 CORE TEAM

POST WELD HEAT TREATMENT PROCEDURE

DOC: CTG-PWHT/PETROSTEEL/008

REV 0

ISSUED ON: 05 December 2011

SREERAM METHIL

Operations Manager

This document is issued for use by CORE TEAM GLOBAL GENERAL CONTRACTING EST.

Neither the whole nor any part of this document may be reproduced in any form without prior

written consent of CORE TEAM GLOBAL CONTRACTING EST.

Microsoft Word - PWHT PROCEDURE FOR PETROL STEEL _ CORE file:///C:/Users/sh/Desktop/Microsoft Word - PWHT PROCEDURE F...

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POST WELD HEAT TREATMENT PROCEDURE

TABLE OF CONTENTS

1. SCOPE

2. GENERAL REQUIREMENTS

3. SPECIFICATION AND CODE

4. EQUIPMENT AND MATERIAL

5. PROCEDURE

6. HARDNESS TEST

7. DOCUMENTATION

ATTACHMENT

1. REQUIREMENTS FOR HEAT TREATMENT FROM ASME B31.3

2. REQUIREMENTS FOR HEAT TREATMENT FROM API 650

3. REQUIREMENTS FOR HEAT TREATMENT FROM ASME SEC VIII

4. PWHT REPORT

5. TIME SHEET

6. CALIBRATION CERTIFICATE


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1. SCOPE

1.1. This procedure outlines the minimum requirement for the external local post weld heat treatment

requirements associated with welded joints of pipe, nozzles, vessels and related components using

electrical resistance methods. The work shall be carried out in accordance with the codes and

specifications described in section 3.0 below.

1.2. Post weld heat treatment shall be performed after all welding and repairs but shall be performed

prior to any hydro test.

2. GENERAL REQUIREMENTS

2.1. This procedure shall be used to determine post weld heat treatment requirement including

equipment, heating methods and inspection techniques.

2.2. The following definitions are applicable to this procedure.

2.2.1. Post weld heat treatment

The heating of an assembly after welding. The types of post weld heat treatment encountered

are stress relieving, normalizing and annealing. For this standard, post weld heat treatment shall

refer to stress relieving.

2.2.2. Stress Relief

Uniform heating to a specified temperature below the lower critical temperature for a sufficient

period of time to relieve the major portion of residual stresses, followed by uniform cooling.

3. SPECIFICATION AND CODE

3.1. The edition of the code and specifications described during the execution of the job requirements will

be applicable.

3.1.1. ASME Boiler and Pressure vessel code section VIII Div. 1 (2010 Ed.)

3.1.2. ASME B 31.3 chemical plant and petroleum refinery piping (2010 Ed.)

3.1.3. API- 650 welded steel tanks for oil storage (10th

Edition, 1998)

3.1.4. SAES-W-010 welding requirements for pressure vessel

3.1.5. SAES-W-011 welding requirements for on-plot piping

4. EQUIPMENT AND MATERIAL

The equipment used by CORE TEAM GLOBAL is purpose built having proven ability in the field.

4.1. POWER SOURCE

Power source will be 380/440 three phase primary supply and gives 3 ph output voltage of

either 60 V to 80 V AC between phase and neutral .The unit is fitted with circuit breaker and panel mounted

cam lock output terminals

4.2 TEMPERATURE CONTROLLER

Temperature controller is a proportional controller for controlling the temperature during

POST WELD HEAT TREATMENT .The deviation between the work piece temp and the set point temp is

proportional to the magnitude of the control signal. K type thermocouples attached to the work piece will be

connected to the temp controller using compensating cables and will control the same. The 6 channel

controller energizes the contractorised heating circuits .Time proportional action is used to control the

heating, cooling and dwell action


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4.3 TEMPERATURE RECORDER

PWHT Temperature shall be progressively recorded using a multipoint potentiometric strip

chart recorder with built in thermocouple reference junction compensation circuit .The calibration of the

recorder will be every three months and a calibration certificate and sticker are provided with the recorder.

The chart speed shall be set at 25 mm/hr and shall record monitoring of all thermocouples and provide

information on the temperature difference and trends during the heating and cooling cycle .Every

thermocouple will be distinguishable on the chart by different color or different number

4.4 THERMOCOUPLE MATERIAL

Thermocouple will be Type `K’ (1/0.711 Ni.Cr./Ni.Al),and Conforms to British Standard BS

1041 Part 4. All thermocouple wire shall have a valid certificate of conformance and shall indicate a tolerance

of less than +/- 0.75% through the temperature range of 400 0

C to 800 o

C as per ANSI MC -96-1-1975

All thermocouples to have initial calibration check and thermocouple wire conformance certificate

4.5 COMPENSATING CABLE

Copper –Constantan compensating cables shall be used to connect “K” type thermocouple

to the temperature controllers and temperature recorder .The copper lead ( positive ,white)shall be connected

to the nickel –chromium conductor (non-magnetic )and constantan lead (negative ,blue)to the nickel

aluminum conductor (magnetic ) of the “K” type thermocouple. Compensating Cable complies with

International Thermocouple Reference Tables BSEN 60584-1 1996

Description:

2 X 13/0.2 mm Copper –Constantan compensating cable type VX, PVC/PVC laid flat BS 1843 color code Positive

white negative blue and sheath cover red

Copper –Constantan compensating cables shall be used with the following conditions:

1. The junction between the copper–constantan compensating cable and the type K thermocouple lead shall

be a minimum of 0.5 m outside the insulated area

2. The acceptable temperature range of the junction between the compensating cable and thermocouple lead

is from 0 to 80 0 C

3. Attachment of thermocouple shall be capacitance discharged direct wire, the gap between not to exceed

6mm .Actual junction to be insulated using thermocouple high temperature Putty to protect from direct heat

source


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4.5 HEATING ELEMENTS

Heating elements used for PWHT shall be flexible ceramic mat heaters of 60 V, 2.7 KW. Standard sizes are 205

X250 mm, 255X205 mm, 305X165 mm, 380X145 mm and 1220X45 mm. Flexible ceramic mat heaters are

designed to use up to 1050 o C. End of the heaters are provided with cam lock plug and socket connections and

the elements are attached by black annealed iron wire and mild steel 12 mm wide banding strap Flexible

ceramic mat heaters can be easily wrapped around the pipes with the following conditions

1. The width of the circumferential band to be heated shall be at least SIX (6) times the thickness of shell

material being welded from both edge of weld ,and should not be less than 25 mm

2. Centre line circumferential gap between two band of elements shall not exceed 30 mm or “t”

whichever is lesser and the longitudinal gap between elements shall not exceed the wall thickness or

50 mm whichever is less ,care shall be taken to ensure that there is no gap in the 6 o’clock position

3. In case if the welding is of two separate wall thickness then the thickness of the thicker pipe will be

considered

4.6 INSULATION

Ceramic fiber mats of thickness 25 mm and size 300 x 600, 600x 600,900x 600, 1200x 600, 1800x600 with SS

wire mesh cover shall be used as thermal insulation .Density of the ceramic fiber shall be 128 kg /m 3

.The

insulation shall extend a minimum distance of 300 mm either side of the weld joint to heat treated .The

insulation shall not be removed until the heat treatment is completed and the temperature is below 150 o

C.

Open end of the pipe shall be closed off to stop air flow through pipe that will lower the temperature of the

inside surface unless the internal surface is insulated .

The number of the layers and extent of insulation will depend on the wall thickness, pipe or fitting diameter,

gradient requirements and the site conditions and the minimum requirement shall be 2 layers of density

128 kg /m 3

5 PROCEDURE

5.1. PREPARATION

5.1.1. Prior to the start of heat treatment the piping shall be inspected to ensure that all restraints have

been removed so it is free to expand and contract.

5.1.2. The work shall be properly supported during heat treatment to prevent sagging and distortion.

5.1.3. Pipe ends shall be blanked off prior to PWHT to prevent the effects of drafts inside the pipe, free

venting shall be observed in the preparation.

5.1.4. The work being heat treated shall be protected from impingement of wind and other types of

inclement weather. It shall be supported (restrained as needed) to prevent war page and other distortion.

5.1.5. Protect flanges faces and threaded connections to prevent damage from scaling during the heat

treatment by a suitable paint or compound (anti-sieze compound/ deoxaluminite). Material shall be heat

resistant and shall be applied by brush and properly covered with ceramics mats during the post weld heat

treatment.


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5.2. THERMO COUPLING

5.2.1. It shall be ensured that there shall be at least one Thermocouple for each separately controlled

zone of heating elements for every 450 mm (24 inch) length of weld seams being heat treated.

If localized PWHT of piping or nozzle welds in used, the following number of equally spaced recording

thermocouples (T/C) shall be used.

A. Pipe Diameter 203 mm or less : 1 T/ C

B. Pipe Diameter above 203 mm up to and including 305 mm : 2 T/C

C. Pipe diameter above 305 mm up to and including 508 mm : 3 T/C

D. Pipe diameter above 508 mm up to and including 610 mm : 4 T/C

E. Pipe diameter above 610 mm : As per the job diameter

Type A

Type B

Type C

Type D


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If localized PWHT of the vessel shall is used, it shall be monitored used at least 4 sets of thermocouples,

with each set consisting of one thermocouple each on the inside and outside surfaces. Each set shall be

placed at 90 intervals around the vessel circumference.

Additional T/C are required if multiple heat control zones are used, in which a control zone is not

monitored by any of the primary T/Cs.

5.4. ALARM SCANNER

The equipment used is incorporated with an alarm scanner which can scan 6 thermocouples

at one time. If one or more gets out of step with other and starts to fall behind an alarm will sound. Similarly if

it exceeds the ‘High alarm’ setting the alarm will sound. If either fault is not cleared within 5 minutes, a second

relay operates which may be used to switch off the faulty circuits. If an alarm sounds, the operator shall stop

wrapping and connecting other welds and returns to the machine.

5.5. POST WELD HEAT TREATMENT

5.6.1. The maximum heating rate beyond 316 oC up to soaking temperature shall not exceed 222

oC/hour

divided by the material thickness in inches, but in no case shall be more than 222 o

C / hour for carbon steel

and alloy steel respectively. Heating and cooling rates are regardless of wall thickness and shall conform to the

PWHT requirement in the individual approved welding procedure.

5.6.2. Soak temperature to be set at a mean difference between the upper and lower limits and the maximum

variation in temperature shall not exceed 40 oC .Soak time starts when all thermocouples reach this

temperature

Carbon Steel Temperature Range: 593 o

C-649 o

C

Holding Time: 1 hour minimum soak time for 25 mm Wall Thickness

Alloy Steel Temperature Range: 704 o

C-746 o

C

Holding Time: 2 hour minimum soak time for 25 mm Wall Thickness

5.6.3. The maximum cooling rate to 316 o

C from soaking temperature shall not exceed 222 oC / hour divided by

the material thickness in inches, but in no case shall it be more than 222 oC/ hour). At

316 o

C the power shall be turned off and the weld will be allowed to cool naturally with the insulation in place.

The insulation shall not be removed before the temperature has cooled to below 150 oC.

5.5. POST CLEANING

After PWHT the TC’s shall be removed and the areas of attachment filled or ground to clean metal. After

thermocouples are removed, the areas shall be visually examined or liquid penetrant inspected. PT report

chart.


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6. HARDNES TEST

6.1. GENERAL

6.1.1. This test method covers the determination of the hardness of the materials, parent metal and the

weldments after PWHT is completed. Acceptable methods for verifying hardness of materials shall conform to

ASTM standard.

6.2. Hardness test shall be carried out with strict compliance set forth in project specification/standards and in

accordance with Brinell Hardness Examination Procedure No: Core Team Global 800-003, Rev. 04.

7. DOCUMENTATION

7.1. Prior to the start of work Core Team Global or fabricator shall prepare a table listing each joint or

component requiring heat treatment, which shall be submitted to Saudi Aramco Inspection for review. The

table shall include the following for each joint or component: location, drawing number, diameter, wall

thickness, material, heating rate, soak temperature, soak time, and cooling rate.

7.2. The post weld heat treatment strip chart shall have a unique identifying number that can be tied back in to

the inspection report.

7.3. The chart speed shall be calculated and noted on the strip a chart at the start of heat treatment.

7.4. The start and end of the soak period shall be clearly mark on each strip chart

7.5. The simple sketch of the element/ heat zone TC layout shall be drawn on the strip chart or attached to it

on a separate sheet of paper.

7.6. Temperature recorders shall be calibrated every three months and a current calibration sticker shall be

maintained on the recorder.

7.7. Hardness test on heat affected zone and weld metals shall be recorded and shall be submitted along with

PWHT reports, sketch or isometric drawing.

7.8. The contractor shall verify the actual thickness of the job and the heating rate and cooling rate shall be

reduced if the thickness exceed the drawing requirement in the actual job as per Para 13.4 of SAES-W-011 and

Para 5.6 of this procedure.


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Client

Project

Order No :

o C

o C

( + - )oC

Hrs Min

o

C/HR

o

C

o

C

APPROVALS

Items Inspected and Process Specification approved befroe PWHT

Weld

Number Diameter Sch/W.T

Joint

Type TC Nos

Tc Color

Code Remarks

Reviewed &Approved By

DATE

Name:_________________________________________________Signature ____________________________Date :_____________________________

NAME

SIGNATURE

Procedure Ref No.

Date

FOR CLIENT

Technician's Name

Thermocouple Removal Area Inspection YES NO

INSPECTED BY

Soaking Period (Min)

Line No/DrgNo /Spool No .

Damage Or Deformation YES NONE

SPECIFICATION AND RECORD OF HEAT TREATMENT Report No

HEAT TREATMENT DETAILS

Restrcited Cooling Rate (Max)

Unrestricted Cooling Rate From To:

Insulation Removed At:

Report No :

Date :

Job No :

Chart No :

Unrestricted Heating Rate To:

Signature (Technician )

Name :

Restrcited Heating Rate of (Max)

Soaking Temparature

Signature (Client )

CHART IDENTIFICATION DETAILS

CORE HEAT SERVICES

Name:_________________________________________________Signature ____________________________Date :_____________________________

INSPECTION AFTER HEAT TREATMENT


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pwht procedure for petrol steel _ core

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