Cracking of welds in the synthesis tower
Thread Content
During the operation of my methanol synthesis tower (of the uniform temperature type, with water flowing in the shell side), there have been several instances where cracks occurred in the welds at the connection point between the steam rising pipe of the tower’s drum and the tower itself, forcing shutdowns. I would appreciate it if experts could analyze the reasons for this, as the tower has only been in use for a little over 2 years.
Thermal expansion issues, or welding problems
1. Welding quality 2. Control pressure of the steam drum 3. Unstable system operation, too rapid pressure increase and decrease
I think the main issue is that the material of the equipment does not meet the design requirements; secondly, the thermal stress generated during the equipment’s manufacturing was not properly calculated.
Weld crackage in shell and tube heat exchangers is a common occurrence; there are also abnormal cases. The reasons are simple: excessive local overheating leading to high thermal stress, poor welding quality, substandard welding materials, inadequate quality of the equipment components such as the tubes, and improper welding techniques – key processes like tube expansion being omitted. Excessive fluctuations in temperature, pressure, or differential pressure during operation can also cause weld crackage. It’s necessary to inspect the cracked areas. What do you do in cases of frequent cracking? The unit must be shut down. And how is the catalyst protected?
I personally also think it’s a material issue; the pipe material is ordinary 20# steel, and I feel that the expansion joints are too small as well. Additionally, their thickness is only 8 mm. This was mentioned during the three inspections and four regular checks – since the project is an EPC turnkey project, the material standards are supposed to meet the required requirements, but in practice they are chosen to be of lower quality. The catalyst refers to the nitrogen pressure retention; it’s the weld on the steam side that has cracked, while the catalyst layer is fine. The main problem is with the pipe section from the shell side of the synthesis tower to the steam drum.
It is mainly likely to be a material issue; it could also be that there are leaks in the tube side, which prevents the welds from withstanding the pressure