Why does the lower head of our buffer tank crack so often?
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The lower head of the three-stage outlet buffer tank of the 6M50 compressor in our workshop has developed cracks on several occasions; even after welding repairs, the cracks reappeared. I don’t know what’s going on. The lower leg of this type of tank is directly welded to the lower head. The vibration is not very high either: diameter 1000 mm, pressure 2 MPa, temperature 130 degrees. I heard that it’s best to weld the legs of the buffer to the middle cylinder; I’m not sure if that’s the reason.
The legs should be welded to the cylinder, as this helps to keep the center of gravity stable; I’ve never seen them welded to the lower end cap. My previous employer specialized in manufacturing auxiliary equipment for compressors in Shanghai, and I’ve also never seen such a design in any blueprints.
Our company is a professional compressor manufacturer, and the buffer tank supports that we design are usually welded to the cylinder body! Does that support in your factory have a shimming plate?
I have been involved in the design of auxiliary equipment for large reciprocating compressors, and this usually involves issues related to the vibration of such machines; these problems are quite complex. Without knowing the specific circumstances, I wouldn’t want to draw any conclusions. Here are a few suggestions: The root cause of cracks lies in vibration, regardless of whether the vibration appears to be severe on the surface； When connecting the legs to the equipment, it is necessary to use shims to prevent excessive local stress at the connection point between the legs and the equipment ； When the equipment is rigidly connected to a reciprocating compressor that generates pulsating loads, it is not advisable to use legs for support
What material is it? It’s probably fatigue cracks
For the compressor outlet buffer tank, even with gaskets in place, vibration problems are likely to occur. The main issue is probably the fatigue load exerted on the lower head; coupled with manufacturing and assembly stresses, this results in complex stress conditions in that area. It is recommended to weld the support legs to the cylinder body. (My personal opinion :) )
The structure is a bit unreasonable, but the main reason is probably vibration
It should be a supporting bracket, so it is welded to the lower head. The enhanced version wasn’t chosen well. It leads to stress failure; it is better to use legs as supports, as this increases the height but also improves the safety factor
The supports for this tank were probably not designed in accordance with JB4712; in that case, they should be welded to the tank body. But according to what you said, I think it might be support brackets of type JB4724. Cracks in the head should not be caused by this issue; I believe they are rather due to vibrations generated by the system
Ear-type supports are used and welded to the cylinder； But since it’s welded to the head, it’s not a big problem even if there are gaskets; it’s better to look for the causes in welding, vibration, and the material of the equipment itself
It should be an ear-type support; if the cracks are indeed caused by vibration, could using a hose for connection be considered?
I’ve really never seen welding supports for end caps; they must definitely be welded to the cylinder body. I’d also like to remind you that in containers under high pressure, any cracks should be repaired as soon as possible to avoid danger – there are many such cases
Legs can be used on the head, but please provide a photo showing where the cracks are located. It should be kept in mind that problems can also occur at the seams of the head, especially in those heads that are first welded together and then shaped
The compressor buffer tank is most likely to have fatigue cracks. A pressure of 2 MPa is already at a quite high level; it’s important to carry out repairs as soon as possible – safety comes first. It’s best to support the legs on the cylinder body, as this minimizes the axial stress on the cylinder. Supporting them on the head is like using a stick to poke at a piece of cardboard