I would like to ask you about the flaw detection issues of fixed tube plate heat exchangers.
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As shown in the picture, how to detect flaw in this weld, there is no need to discuss surface detection, radiography is the best, followed by recordable flaw detection, if it involves the assembly sequence, please tell me a few words, thank you! :) There is no need to discuss the topic of exemption from flaw detection and structural improvement, or even the statement that flaw detection is impossible. We just discuss how to detect flaw, and there is no need to expand on other issues. In addition, please answer it if you have actually encountered it and solved it, so as not to mislead friends who have never been in contact with it.
RT can be done, as long as there is a distance of 20mm between the docking boss and the film can be attached. After the specific design is completed, I will ask the person who does the non-destructive testing.
Stick it outside? There is obviously not enough 20mm inside. The flaw detector here said it can't be done. I'll go and confirm why it can't be done. Even after RT can be done, there must be a circumferential weld that cannot be radiated, and then TOFD is used.
The flaw detection personnel here also said that they can't do it and can only do UT.
Does the Pot Inspection Institute agree? Our pot inspection office disagrees, and this is the crux of the problem.
TOFD has requirements for thickness (maybe more than 16mm) and extended docking length (due to dual probes). It is recommended to do UT+MT. My personal suggestion is for reference only.
There should be no problem with the thickness. This structure will only be used when it is greater than 4.0MPa, and it is clearly stated on 150 that equipment not greater than 800 can be exempted from inspection, so this problem will only exist when it is greater than 800 and 4.0Mpa. Then I said that the TOFD we did was to leave the last girth weld in the middle of the shell, that is, the weld to the tube plate was welded in advance.
Is it appropriate to place the closing seam in the middle of the tube heat exchanger? What if the baffles and other internal parts happen to be near the welding seam and affect the welding? It is recommended that you take a look at the assembly sequence in your production workshop before making a decision. We have done a lot of UT+MT joints between tube sheets and cylinders, and they are recognized by the design institute and the special inspection institute. (Personal suggestions are for reference only)
In this pot inspection institute, one place or one person has different opinions and cannot communicate. Let’s just talk about this issue. Even if the weld coefficient is 0.6 when it cannot be detected as mentioned in the standard, the pot inspection institute will not agree with it. Why should you take 0.6 if it can be measured? Hey, there are other problems that often arise.
If the drawing is issued by the design institute, then proceed according to the requirements of the drawing. If not, it has nothing to do with whether the design institute approves it or not. The weld is forced to be placed in the middle, and there is no problem. As for the problem you mentioned, this is only one of the considerations. There are also avoidance openings, avoidance supports, and sufficient TOFD space, etc. These will all be drawn up before production. There is no problem with this. The order of the workshops is not static within a certain range, and we have communicated long ago that it is feasible. This issue is similar to whether a fixed tube sheet heat exchanger has a concealed or exposed penetration.
Always pay attention to this issue! Looking forward to more people participating in the discussion!