Cracks appear in the heat exchanger expansion joint
Thread Content
The expansion joint material of the heat exchanger, in which low-pressure steam is used on the shell side, is 00Cr17Ni14Mo2. After being in use for one year, cracks appeared; TIG welding was carried out, but new cracks emerged immediately after welding, and further cracks appeared not long after that. What should be done? If a new heat exchanger is installed, does the material of the expansion joint need to be replaced as well? Seeking help from experts
It’s not 00Cr17Ni14Mo2, it’s S31608
It depends on what type of crack it is – whether it’s a crack in the weld or in the base material – as well as whether there is intergranular corrosion or stress corrosion in the material. As for cracking immediately after welding, extra caution is needed, as the tendency for stress corrosion cracking is high.
In the situation described by the poster, stress corrosion is likely to have occurred. First, the medium involved needs to be considered; if its influence can be ruled out, then the environment should be examined to see whether chlorine ions are present in the air. I have experienced this phenomenon: cracks appeared in the pipes, and those cracks grew worse as welding continued; in the most severe cases, a hole would form with each weld. It is possible that no further solution treatment was carried out after the expansion joint was formed, resulting in tensile stress and thus stress corrosion. What material is the casing made of? Low-alloy steel, maybe Q345R? For the new heat exchanger, the expansion joints need to undergo solution treatment after being formed.