7800 PWHT-(Storage Tanks) Rev.a _1

The Company with the Strength of Steel

PROCEDURE FOR POST WELD HEAT TREATMENT OF STORA STORAG GE TANKS TANKS

PROCEDURE NO.: 7-8-00 / JF - 777 UNTREATED ASL STORA STORAG GE TANK

A Rev.

26.11.2016 Date

Issued for Client Approval Revision Description

M. Ibrahim

Z. Ramadan

Ib. Nageeb

Prepare By Welding Engineer

Reviewed By: QC Sup Super erin inte tend nd

Approved By: QC Manager


POST WELD HEAT TREATMENT (STORAGE TANKS)

Procedure :7-8-00/JZ-777 Rev / Date : A / 26.11.2016 Page : 1 of 5

TABLE OF CONTENTS SECTION

TITLE

PAGE

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Cover Page...................................................................

0

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Table of Content............................................................

1

1

Scope............................................................................

2

2

References…………………..........................................

2

3

General Requirements..................................................

2

4

Heating System……………...........................................

2

5

Temperature Control….….............................................

3

6

Thermocouples & Thermocouple Extension….………..

3

7

Thermocouple Positions………………………...…...…..

3

8

Temperature Record…………………………….………..

3

9

Procedure………………………………………...………..

4-5

10

Documentation & Records…………………...…………..

5




1

Scope

1.1

This procedure describes all the requirements for Post Weld Heat Treatment of shell / re-pad and cleanout door assembly of Storage tanks in a furnace as per API 650 & API 620.

2

References

2.1

API 650 11th Edition (2011).

2.2

32-SAMSS-030

2.3

SAES-W-017

2.4

Applicable Welding Package (WPS, PQR).

3

General Requirements

3.1

Before applying the detailed requirements, satisfactory weld procedure qualifications of the procedures to be used shall be performed in accordance with all the essentail variables of ASME section IX including conditions of postweld heat treatment or lack of postweld heat treatment.

3.2

Prior to the start of PWHT, components shall be checked to ensure that all restraints are removed, the component is free to expand and contract and suitable and sufficient support are used.

3.3

All machined surface, such as flanges faces, threaded bolts holes, threads, etc. Shall be protected from oxidation during the heat treatment by coating with de-oxaluminite or other suitable material.

3.4

All PWHT chart records shall be submitted to Welding Engineer for review and approval.

3.5

Suitably trained Presonnel shall be employed for operation of PWHT Furnace.

4

Heating System

4.1

The Specification of PWHT Furnace as follows 

Furance type : Transport loading type (W(6) X H(7.5) X L(25) Meter)

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Loading Capacity : 300Ton/Charge Max.

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Maximum Operation Temperature : 750 C (Normal : 700 C)

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Coumbustion method : Diesel Burner (Ignition LPG)

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Ignition system : LPG high voltage discahrge ignited by the Flame

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Main Fuel : Diesel

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Burner Quantity : 8 set

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Burner Capacity : 1000000 Kcal/h/set

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Electricity : 380V 3P 60Hz

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Blower : Motor : 11KW 3P x 8 set

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Air Pressure & Air Flow : 700mmAq & 35CMM

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Local control Panel & Main Control Panel




5

Temperature Control

5.1

There are eight Local Control Panel in the Furnce for the burner control. The Local Control Panel to drive the burner control unit as fundamental from air pressure control ignition, fuel valve control etc.

5.2

The Burners shall be adjusted manually, by continous reference to the temperature recording instrument, adjusting fuel and airflow in a manner such as to ensure that parameters and constraints of the specification are fully met, to achieve a heating balance throughout the assembly.

5.3

The location of thermocouples describes in Section 7 of this procedure, shall be determined so as to provide a good indication of the overall distribution of heat throughout the assembly, any discrepancy shall be investigated.

5.4

The actual temperature range for the soak period, as recorded by thermocouples, shall not have a spread of more than 40°C.

6

Thermocouples & Thermocouple Extension

6.1

Thermocouples shall be Type K(Chromel-Alumel) or Type J(iron-Constantan).

6.2

Thermocouples shall be attached to the workpiece by the direct wire capacitance discharge welding method.

6.3

All extension cables, compensating cables, and jumper cables in the measurement or control circuits shall be the specified thermocouple wire or the matching extension wire.

6.4

The thermocouple to compensation lead connection shall be a minimum of 0.5m from the heated zone, and that the temperature at the junction is to be in the range of 0-80°C.

7

Thermocouple Position

7.1

Thermocouple sahll be located on the nozzle to shell / pad assembly surface to ensure that all positions are properly and uniformly heated. The thermocouple locations shall include: a- The thinnest major component b- The thickest member.

7.2

Sufficient thermocouples must be used to ensure that the welds and heat affected zones achieve the uniform temperatures.

8

Temperature Recording

8.1

Thermocouples and a calibrated temperature chart recorder shall be used to provide an accurate and legible record of all PWHTs. All charts shall be marked with the date and sufficient information to uniquely identify the vessel (orjoint/component for localized PWHT) being heat treated. Multipoint chart recorders shall clearly differentiate/identify each channel/point by use of different colored inks or automatic number stamping.

8.2

Temperature recorders shall be calibrated every three months and a current calibration sticker shall be maintained on the recorder. The calibration frequency may be extended to 12 months with the approval of Saudi Aramco Inspection if the documented calibration checks for that particular recorder demonstrate acceptable accuracy for a suitable period..



9

Procedure

9.1

API 650 Storage Tanks


9.1.1 All flush-type cleanout fittings and flush-type shell connections shall be thermally stressrelieved as an assembly prior to installation in the tank shell or after installation into the tank shell if the entire tank is stress-relieved. The stress relief shall be carried out within a temperature range of 600°C - 650°C (1100°F - 1200°F) for 1 hour per 25 mm (1 in.) of shell thickness. The assembly shall include the bottom reinforcing plate (or annular plate) and the flange-to-neck weld. 9.1.2 When the shell material is Group I, II, III, or IIIA, all opening connections NPS 12 or larger in nominal diame-ter in a shell plate or thickened insert plate more than 25 mm (1 in.) thick shall be prefabricated into the shell plate or thickened insert plate, and the prefabricated assembly shall be thermally stress-relieved within a temperature range of 600°C - 650°C (1100°F 1200°F) for 1 hour per 25 mm (1 in.) of thickness prior to installation. The stress-relieving requirements need not include the flange-to-neck welds or other nozzle-neck and manholeneck attachments, provided the following conditions are fulfilled: a) The welds are outside the reinforcement b) The throat dimension of a fillet weld in a slip-on flange does not exceed 16 mm (5/8in.), or the butt joint of a welding neck flange does not exceed 19 mm (3/4 in.). If the material is preheated to a minimum temperature of 90°C (200°F) during welding, the weld limits of 16 mm (5/8in.) and 19 mm (3/4 in.) may be increased to 32 mm and 40 mm (1 1/4 in. and 1 1/2 in.), respectively. 9.1.3 When the shell material is Group IV, IVA, V, or VI, all opening connections requiring rein forcement in a shell plate or thickened insert plate more than 13 mm (1/2in.) thick shall be prefabricated into the sh ell plate or thickened insert plate, and the prefabricated assembly shall be thermally stress relieved within a temperature range of 600°C – 650°C (1100°F – 1200°F) for 1 hour per 25 mm (1 in.) of thickness prior to installation. 9.2

API 620 Storge tanks

9.2.1 Tank sections that have a nominal thickness of wall plate greater than 1 1/4 in.at any nozzle or other welded attachment and nozzle necks whose thickness at any welded joint therein exceeds (D + 50) / 120 shall be thermally stress relieved after welding. Thickness of compression rings are not considered in the determination of thermal stress relief requirements. When thermal stress relief cannot be applied to welded assemblies of these parts after erection, all such assemblies, particularly around openings and support attachments, shall be made in the shop and shall be thermally stress relieved before shipment. 9.2.2 A minimum temperature of 1100°F (600°C) shall be maintained for a period of one hour per in. of metal thickness (maximum metal thickness of the tank wall plates affected).

Table 1

9.2

General

9.3.1 The temperature of the furnace shall not exceed 600°F (315 C) at the time the part or section of the tank is placed in it. 9.3.2 The rate of heating in excess of 600°F (315 C) shall be not more than than 400°F (222°C) per hour divided by the maximum metal thickness, in inches., of the wall plate being heated, but in no case shall it be more than 400 °F/hr (222°C/hr)




9.2.3 During the heating period, the temperature throughout the portion of the tank being heated shall not vary more than 250°F (140°C) within any 15-ft (4.6m) interval of length and when at the hold temperature not more than 150°F (85°C) throughout the portion of the tank being heated. 9.2.4 During the heating and holding periods, the furnace atmosphere shall be so controlled as to avoid excessive oxidation of the surface of the material being treated. The furnace shall be of such design as to prevent direct impingement of the flame on the material. 9.2.5 At temperatures over 600°F (315°C), cooling shall be done in a closed furnace or cooling chamber at a rate not greater than 500°F (280°C) per hour divided by the maximum metal thickness, in inches of the plates affected; in no case shall the rate be more than 500°F (280°C) per hour. At temperatures of 600°F (315°C) and below, the material may be cooled in still air. 9.2.6 The rates of heating and cooling need not be less than 100 °F/hr (55°C/h). However, in all cases consideration of closed chambers and complex structures may indicate reduced rates of heating and cooling to avoid structural damage due to excessive thermal gradients.

10

Documentation & Records

10.1

The documentation information will comprise of the following: 

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

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Approval of relevant heat treatment procedure and / or specification, and chart recording receipt. Heat Treatment Data sheet (Deatails of thermocouple layout & traceability to the recording chart). Temperature chart, fully identified and referenced. The chart shall also identify the heat treatment specification, chart speed, date of operation, job and component number. Recorder Test Certificate and Thermocouples conformation.

7800 PWHT-(Storage Tanks) Rev.a _1

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