An older high-pressure (30,000 psi) hyper-compressor, installed in a Low-Density Polyethylene (LDPE) plant on the Gulf Coast, USA, faced significant operational challenges. The compressor experienced repeated failures of the connecting-rod big-end bearings, leading to frequent and costly replacements.
This compressor experienced several connecting-rod big-end bearing failures due to inadequate crush within the housing in the conrod, resulting in fretting on the bearing’s external surface and fatigue failure of the antifriction metal, necessitating repeated replacements.
Fig 1. MALB connecting rod with FEA
The fretting phenomena can be related to a low level of specific contact pressure between conrod and the bearing shell. This is noticeable in conrods equipped with bearings with a thick shell. For such bearings high bolt preload is necessary for sufficient contact pressure. In some compressors such fretting wear for the conrod body is recurrent, and repairs (such as hand polishing) are required more often. Frequent repairs can lead to distortion of the original shape and further integrity problems with the bearing itself.
CST conducted a Root Cause Analysis (RCA) that confirmed the fretting phenomenon through Finite Element methods (FEM) simulation. Subsequently, the big end bearing and cap bolts were redesigned to optimize contact pressure and prevent relative movement, leading to the refurbishment of the connecting rods accordingly.
