Failure Analysis Stress Analysis Redesign

Failure Analysis / Stress Analysis / Redesign: We have carried out analysis of machinery failures in order to determine root causes. In addition, it is sometimes necessary to enhance the design of machinery to improve reliability because the mean time between failures (MTBF) is not acceptable. The pictures below show a refinery 6 ins OVTB 2 stage flashed crude oil pump which experienced failed bearings, failed mechanical seals and failed shafts over many years.

Original Design from Manufacturer	Improved Design

Original Design	Improved Design

Original Design	Improved Design

The cause was that the pump operated very close to its first lateral critical speed. The impeller hubs were bored out and a larger diameter, reduced length shaft was designed and fitted. The old stuffing box castings were redesigned to incorporate inboard mechanical seals and the shorter shaft. To reduce the overhung mass and inertia, the original large mass high inertia coupling hub was re-machined. The thrust bearing was changed to angular contact bearings in the ‘back to back’ configuration at the NDE and the DE bearing was changed to a cylindrical roller to accommodate thermal growth. The overall vibration level reduced from 28.5 mm/sec rms (1.122 ins/sec rms) to 0.9 mm/sec rms (0.0354 ins/sec rms) and reliability was no longer an issue.

We can also offer failure analysis on rolling element bearings, journal bearings, active magnetic bearings, mechanical seals, rotors, structures, piping etc. This service may be useful for warranty claims.