Equipment for local and volumetric PWHT (heat treatment of welded joints)

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STO Gazprom 2-2.3-251-2008

07.04.2019 21:06:00

Dear friends!

This document has the name "Assembly, welding, heat treatment and quality control during the repair and modernization of case technological equipment of GAZPROM OJSC".

Лого Газпром

This standard applies to the assembly processes, manual and mechanized arc welding and heat treatment, as well as to the quality control of welded joints during the repair and modernization of Gazprom's case technological equipment - steel vessels and apparatuses operating under pressure not exceeding 16 MPa (160 kgf / cm2) or without pressure and at a wall temperature not lower than -70 ° С.

Requirements for heating modes before and during welding are specified in clause 14.7.2.

General requirements for local heat treatment of welds after welding are specified in section 16.

16.1 General requirements for the heat treatment of repair welded joints.

16.1.1 This section is designed in accordance with the requirements of ПБ 039576903, ПБ 039584903, ОСТ 26291, РТМ 26944982, РД 558997, ОТУ 3901.

During repairing under the conditions of the installation site, local heat treatment of repair welded joints, volumetric out-of-furnace heat treatment of the vessel in whole or in part, or combined using local and volumetric heating simultaneously can be performed.

16.1.2 Volumetric out-of-furnace heat treatment is recommended for large volumes of repair welding.

16.1.3 During the case equipment repairing , the following types of technological heating and heat treatment are used:
- heat treatment to remove hydrogen (degassing) before welding when repairing equipment that was in operation in environments containing hydrogen sulfide;
- preliminary and concurrent heating during welding and other types of hot work;
- thermal rest in case of long breaks in work with martensitic steels (as an option for intermediate stress relieving in the absence of mechanical impact on the product);
- intermediate stress relieving, in the case of welding of hard knots and correction of defects with a large volume of deposited metal during the development of an individual technological process
- post-welding (final) heat treatment according to the regime of high-temperature stress relieving or stabilizing annealing to reduce welding stresses and improve the properties of the weld metal and the heat-affected zone.

16.1.4 Parts and components that have passed an intermediate PWHT is later on subject to mandatory high-temperature stress relieving. After stress relieving, the time until the final heat treatment is not regulated.

16.1.5 Static and dynamic loads on the vessel should be excluded as far as possible before the final heat treatment.

16.1.6 Heat treatment works are carried out in accordance with the work instructions (technological process), which are developed taking into account the requirements in the passport (drawing) of the apparatus, repair documentation and actual part.

16.1.7 Welding without heat treatment of internal and external devices on the mounting site to special plates and brackets welded to the body of the device and undergoing heat treatment with it is allowed without heat treatment.

16.1.8 It is allowed to weld internal and external devices without subsequent heat treatment according to the high-temperature stress relieving mode to the bodies of previously heat-treated vessels and apparatuses made of carbon and low-alloyed silicon-manganese (20K, 09Г2С, 16ГС, etc.), provided that the size of the weld is not exceeds 8 mm.

16.1.9 Cancellation of heat treatment or change of modes can be made by agreement with the design organization, the developer of repair documentation or the developer of the standard, with the exception of cases specified in 16.1.7 and 16.1.8.

16.1.10 To conduct heat treatment, a special group should be organized, consisting of:
- from an engineer (team leader) who has permission to supervise heat treatment;
- an operator-thermist on mobile thermal installations, respectively, for local or out-of-furnace volumetric heat treatment that has finish special training, accordant qualification tests and has a certificate of the right to carry out work;
- a specialist to service thermal equipment and instrumentation.

16.1.11 The heat treatment should be started after checking the documentation confirming the quality of the welding work. In the case of defects correctionby welding after heat treatment, the repair site must be subjected to repeated heat treatment.

You can download STO Gazprom 2-2.3-251-2008 here.

Regardless of the regulatory document you are using, our managers can help you to choose right units, heating elements and other components for local heat treatment of welds.

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