Reasons for crack formation
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This is a shell-and-tube heat exchanger; the material of the shell in the shell side is S30408, with tubes of φ273 and a thickness of 6 mm. The cracks appeared on the base metal at the weld seam between the expansion joint and the shell. At the user’s site, a leak was detected before any pressure was applied; let’s analyze the reasons.
Are the materials of the shell and the expansion joint compatible? Is the material of the welding rod up to standard?
The shell material is the same as that of the expansion joint; weld material A102 is suitable, and moreover, the crack did not appear at the weld seam.
If he has to consider so many things as you say, can his welding still meet the requirements of the process? Won’t that result in many cracks?
Let’s check the material first, take a spectrum to see if there are any issues with it. Check again whether there are any weld repairs in that area, and whether excessive local stress has resulted from inappropriate repair methods. As for whether there were any violations in processes such as alignment and welding during manufacturing, only the manufacturing unit knows.
This area also falls within the heat-affected zone of the weld; it is necessary to check whether there are any issues with the material. An ultrasound inspection should be carried out around the weld to determine if there are any internal cracks in that area. If such cracks exist, they should be removed promptly and the area rehealed
This crack must have appeared later; there were no issues during the pressure testing in the factory.
Check whether there are any issues with the material, as well as the heat-affected zone of the weld. It appears that these areas correspond to the starting and ending points of the welding rod; stress concentration may occur due to deviations during alignment, and force applicators were used to level out those areas
This is very important and should be written on the first floor. Write about what is easily overlooked.
If it occurs later on, the stress corrosion condition in this area should be considered.
It hasn’t been suppressed yet; it probably hasn’t been used yet, right?