How to fix a heat exchanger leak
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Our plant has an air preheater that is a fixed-tube-sheet heat exchanger. The tube carries steam, while the shell carries air. Both the fixed tube sheet and the tube material are stainless steel (304), with fins on the tubes. For some reason, after several months of operation, the welds between the tubes and the tube sheet kept leaking. The equipment is made for our factory’s maintenance department. The welding was not followed by heat treatment; given how good the material is, shouldn’t it be treated? Also, with the equipment being so large, I’m not sure how to carry out heat treatment
It’s due to welding issues; it is recommended to use surfacing and heat treatment, as the pressure of the medium in the air preheater is too high
The post about air preheaters with over 500,000 views – please don’t just disappear like this! Help! ! ! ! ! ! ! ! ! !
Is the weld leakage due to cracks, pores, or incomplete welding? Is it regular?
304? Heat treatment? In general, 304 material does not require heat treatment. Leaks between pipes and tube sheets are mostly caused by welding. It is caused by poor welding skills or inadequate operation of the automatic welding machine. Other reasons should also be looked for.
Should the pipes be joined by expansion welding with sealing, or by strength welding?
It is necessary to carefully observe the shape of the cracks. If the welds of 304 steel are not treated properly, many cracks will appear; however, different shapes of cracks result from different formation mechanisms, and blind treatment will only provide temporary solutions rather than addressing the root cause.
It is recommended to conduct a PT test first to determine the cause of the leakage: is it cracks, pores, or corrosion? Only then can solutions be considered. Different situations require different solutions
There may be issues with the welding quality; perhaps minor cracks occurred during welding, and the high steam pressure led to stress corrosion. The material is so good and doesn’t require heat treatment. I don’t have any practical work experience, so I really don’t know how to solve this!
Based on what the poster has said, this device is likely a typical \"product without any proper certifications.\" Given the high value of the equipment, in response to this situation, it is recommended to: 1) Contact personnel responsible for the design, manufacture, and inspection of pressure vessels to conduct on-site analysis and inspection, and develop a specific plan for rectification ； 2) Repaired by professionals from specialized manufacturing plants (pressure vessel manufacturers, certified welders, and non-destructive testing personnel, etc.) ； 3) There are quality certificates issued by the repair factory, etc. There’s no need to waste time here; take action right away.
Is there a problem with the quality of the steam? For example, if the desalination effect is poor and chloride ions are present, it is not recommended to use austenitic stainless steel in areas where steam is present.
Was the air preheater designed in-house? I’m not aware of the welding method used for joining the tubes to the tube sheet; it is recommended to first check the design drawings to determine whether a strength-enhancing seal weld connection is being used. Then, examine the manufacturing process to see if it matches the design specifications. It’s also necessary to check whether the dimensions of the holes in the tube sheet for the heat exchange tubes are within acceptable limits, whether there are any issues with the materials used for the tube sheet and heat exchange tubes, and whether there are problems with the welding materials used. I believe that there must be some issue in one or more of these aspects, and identifying those issues will allow us to take appropriate action: lol. As for welding quality issues, I think equipment of such importance should not be welded by beginners: Q.
There are many welding-related issues; when welding stainless steel tube sheets to tubes, it’s important to maintain proper levelness, and it’s best to conduct a surface inspection after welding.
The main problem might be welding issues； The second is a structural issue with the equipment itself; due to thermal expansion and contraction, stress tends to concentrate between the tubes and the tube sheet. Our company has two air preheaters, fin-type, with a temperature of 150 degrees and a flow rate of over 30,000; the material used is carbon steel. It was done by a company before; steam leakage occurred after three months, and catalytic oxidation led to corrosion of the subsequent equipment ； I switched to another company, left a 40% warranty deposit, made slight modifications to the design, and it hasn’t leaked after being in use for over a year.
Stainless steel does not require heat treatment; I agree with what was said on floor 15 – it might be a welding issue. Organize people to prepare the rectification plan.
Welding issues are inevitable; if the tubes are thin while the tube sheets are thick, cracks can occur if a connection method that takes into account strength considerations and proper sealing is not used. A root pass must be made using TIG welding. Re-examine the welding plan. During construction, on-site supervision is essential; don’t let them deceive you.
The tube sheet has a thickness of 6 mm, while the tubes have a diameter of 25 mm and a thickness of 3 mm. This equipment is manufactured solely by our factory and is intended for use only within that factory. There are no specialized design drawings either. The tube should extend 2mm to 3mm beyond the tube sheet. Everyone’s discussions are really emotional
This type of stainless steel does not require heat treatment. The main issue is gap corrosion that occurs between the tube sheet and the tubes; if there are cracks near the welds, it is stress corrosion, while other problems are likely related to welding issues.
How can the tube sheet thickness be 6mm?