Failure Analysis

It's a must to have a Root Cause Analysis (RCA) program. This is one part of the pump reliability puzzle required to be effective in our businesses.

by Robert L. Matthews

It's a must to have a Root Cause Analysis (RCA) program. This is one part of the pump reliability puzzle required to be effective in our businesses. The easiest way to start an RCA is to simply ask "why?" until you can't ask it again.

What happened? Seal failure? Why? What else could it be? Why?

In the case of seal failure, for example, statements such as "seal", "seal leak", or "seal blow out" don't constitute a failure analysis. Not only does this not give any clue as to why the failure happened, it doesn't even give enough information to track down the cause. Too often operations will shutdown equipment with a seal failure and it was a gasket leak at the seal or an o-ring under a sleeve and not the seal at all. Since this costs plants so much unnecessary repair cost, it's where operator awareness to rotating equipment is so important.

Failure analysis is using all the information from the change-out tag, disassembly checks, visual component inspection, operator interviews, and any added scrutiny — then you try to determine what caused the failure and why. This involves two steps. The first is determining exactly what happened, and the second is determining why it happened. The second step is key to preventing the failure in the future, and is the whole reason for doing the analysis.

Let's walk through a quick example of Root Cause Analysis.

A pump has sprayed caustic from a mechanical seal and the operations night crew shuts it down and starts the standby pump. Shift maintenance is called to pull the pump. The pump has a failed mechanical seal and, as the rotating assembly is pulled, obvious visual signs point to the impeller clashing and rubbing the casing. This would have caused the seal to fail. Next the radial bearing labyrinth is damaged and oil has leaked out, causing the bearings to fail — and that would cause impeller clashing. The bearing housing is opened and the oil gone which we know will knock out the bearings, but inspection of the pump sight shows that oil was in the housing and had leaked out. The front or wet end bearing cap is pulled and there's a crack in the gasket. The crack wasn't noticed at installation because it was on the back side. The gasket was cracked because store room workers had folded the gasket — the last "why?". You get the picture. With training in the store room and inspections in the pump shop this never happens again.

Root cause analysis works and the payback is worth the effort.


About the Author: Reliability manager for Houston-based Royal Purple Ltd., Bob Matthews has 35+ years of pump industry experience — from hands-on to supervision, in-plant maintenance management, consulting and training. He has taught advanced pump classes for Fortune 500 companies, universities, the Vibration Institute, ASME and FSA. Contact: www.royal-purple.net

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