The stainless steel bolts at the pump outlet have loosened – what should I do?
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I’m facing a tricky issue now: can carbon steel bolts be used on the stainless steel flanges of pumps with significant vibration (diaphragm pumps)? Currently, stainless steel bolts are being used in the design, but they have loosened due to vibration near the expansion joints at the pump’s inlet and outlet. What should be done? Is it because stainless steel bolts don’t perform well under vibration? Stainless steel is relatively soft, so it cannot be tightened properly, and its strength at room temperature is lower than that of carbon steel bolts; it tends to soften when subjected to vibration, and once it softens, it loosens up. I’d like to change it to carbon steel bolts with spring washers; please give me some suggestions!
The key to solving this problem isn’t necessarily choosing between carbon steel and stainless steel bolts. In my opinion, the crucial aspect is dealing with vibrations; as long as those vibrations are controlled, the bolts, as connecting elements, won’t loosen so easily!
If it is single-ended, change it to double-ended; if it has a single nut, a locknut can be added. If the pipeline vibrates excessively and it is a pipeline at the pump’s inlet or outlet, vibration damping must be implemented. Vibration reduction can be approached from aspects such as the process and brackets.
Reply to 4# lewismelon: That type of pump is different from ordinary centrifugal pumps; centrifugal pumps have very little vibration, while diaphragm pumps vibrate in a pulsating manner. That’s why expansion joints are installed at both the inlet and outlet of the pump – it is at these expansion joint locations that the bolts tend to loosen. Thank you for your reply. I feel that using spring washers and double nuts is quite effective.
Reply to 1# 45791978: Does adding a stop washer make it work much better?
The specifications do not require that stainless steel flanges must be secured with stainless steel bolts. As for the bolts on the inlet flange of diaphragm pumps coming loose, it is not a problem related to whether the bolts are made of carbon steel or stainless steel. The pulsating vibrations of diaphragm pumps represent cyclic stresses; if the damping effect is insufficient, this issue can be addressed by considering the choice of expansion joints – selecting more suitable expansion joints or flexible connectors. It is best to use double-headed bolts along with spring washers