Failure analysis of flexible metal hose at compressor discharge

Flexible hoses are sometimes placed at compressor discharge to minimize the effect of vibrations on piping and vessels. Doing well for this purpose, these elements can suffer dynamic loads from gas pulsation and fail. The root cause of the failure of a flexible connection at the discharge of an oil distillery propane alternating compressor is investigated. The connection is a 150 mm stainless steel corrugated metal hose with an external braid. The failure took place by overload of the braid, after wear of the wires. The fractures in the wires were consequence of fatigue crack propagation in previously worn areas. It was found that the flexible connection was under a larger working pressure than the maximum allowable as defined by the manufacturer. The failed flexible had thinner wires and different braid design than those previously used by the user. Recommendations include procedures to verify dimensions previous to assembly and to increase the inspection frequency of these elements, as well as to verify vibration levels of the connected machines. An elastomer material placed between corrugated and braid would diminish the rate of wear caused by vibrations.