Pressure pipelines and pressure vessels: regarding radiography, the sequence before and after heat treatment (Reward: 2 charm points – Deep Blue Expectation)

I’m not quite sure about pressure pipelines! I’m not in this business; as for pressure vessels! I can give a brief overview! Radiographic testing of pressure vessels refers to this RT inspection (non-destructive testing). After the equipment is manufactured, all welds must undergo non-destructive testing based on the weld coefficient, in order to ensure the quality of the welds. Radiographic testing is used to determine the extent of defects in the welds; if these defects exceed the specified limits, the welds need to be reworked and welded again. Heat treatment, on the other hand, is a process used to relieve stress in the equipment (welds). If heat treatment is carried out first and then radiography is done, and it is found that the weld is not up to standard, re-welding is required followed by additional heat treatment.

I’ve never worked on pipelines, but by checking the GB/T20801-2006 standard, it doesn’t seem that flaw detection is required after heat treatment. Section 11.3.11.1 of the \"GB50236-98 Code for Construction and Acceptance of Welding Works on Field Equipment and Industrial Piping\" states that post-weld heat treatment of welds shall be carried out after the visual inspection of the welds and the completion of the specified non-destructive testing. However, welded joints with a tendency to reheat cracking should undergo surface non-destructive testing once after welding and once after heat treatment. Do you mean this?

The last edit to this post was made by You Er Bu Ji on 2011-5-19 at 16:44. From another perspective, your question can seem to be answered as follows: Containers are generally large and their heat treatment costs are high, so they are placed later; pipes, on the other hand, can undergo local heat treatment using electric heating, which is less costly, allowing them to be placed earlier.

For the thick-walled pipes P11 and P22 used in ethylene plants, flaw detection is carried out after heat treatment; the acceptance standard SH3501-2002 does not specify anything to the contrary (except for materials prone to reheat cracking). Similarly, for the pipes P91/T91 and P92/T91 used in power plants, flaw detection is performed after heat treatment, and the acceptance standard DL/T869-2004 also does not specify anything different (except for materials prone to reheat cracking). Other materials such as 15CrMo and 12Cr1MoV are also subject to flaw detection after heat treatment. It’s not clear whether this is due to convention or as a precautionary measure. Of course, it is possible to conduct flaw detection on these pipes before heat treatment, in order to ensure that the welds are of satisfactory quality and to avoid the hassle of having to repair them after heat treatment.

This post was last edited by SuperFree2316 on 2011-5-23 at 17:58. Reply 1# WANGJIABAO: The reason is as follows: 1. There are many locations where pipeline construction takes place, and heat treatment requires a lot of time; to facilitate work and reduce the risks associated with radiation on site, flaw detection is carried out in a centralized manner after heat treatment. Additionally, when issues are found during pipeline welding and the pipes are rewelded, flaw detection after heat treatment is simpler； 2. Containers are generally subjected to heat treatment after flaw detection during manufacturing; in order to prevent the need for multiple heat treatments due to minor welding defects, flaw detection is carried out first, and materials prone to thermal stress cracks are inspected again after heat treatment

Radiography is carried out to check the quality of the welds, and the first-pass success rate for welds generally cannot reach 100%; therefore, the heat treatment of large containers is performed after radiography

After heat treatment, welding on the container is no longer allowed; if imaging is performed after heat treatment and defects are found in the welds, it is not possible to carry out repair welding

RT is required before and after heat treatment: the first RT is conducted to identify any possible defects, and RT is performed again after those defects are repaired; the subsequent RT is carried out to detect any \"new defects\" that may have arisen during PWHT, and RT is done once more after those defects are fixed.

For containers, welding repairs are generally not allowed after heat treatment. If RT is performed first and the repaired weld is then welded again, heat treatment will have to be carried out once more, which means multiple heat treatments and is not very economical.

If new defects arise during the PWHT process, then \"doing nothing\" is the correct approach; this is not an economic issue, but rather a question of whether the product can meet the required standards.