Magnetic Particle Inspection of Reciprocating Compressor Cylinders Using a Fixed AC Coil

摘要

Unique magnetic particle methods are sometimes required for testing surfaces that are not accessible to the use of conventional inspection equipment. The failure of a hydrogen service reciprocating compressor cylinder initiated the development of just such a method. A reciprocating compressor 4th stage recycle cylinder, in hydrogen service, suffered a fatigue failure that initiated in the fillet of the inboard suction valve shelf. This cylinder, specified to AISI 4340 forgings, was designed for a suction pressure of 11,720 kPa (1,700 psig) and a discharge pressure of 21,720 kPa (3,150 psig), with suction and discharge temperatures of 57.2 and 121℃ (135 and 250℉) respectively. Any through wall cylinder failure could have catastrophic results. Thus, an accurate nondestructive testing (NDT) procedure enabling the detection of cylinder valve shelf defects was required.