Recently on the RCM2 LinkedIn Group, an interesting discussion emerged on the differences between root cause and failure mode? Worth sharing…

Adhen Utomo, Mechanical Engineer at Kaltm Prima Coal in Indonesia, asked this question, “what is the difference between root cause and failure mode?”

Denis Marshment, long time RCM2 Practitioner and Director of Asset Dynamics Asia. Stated that “Root cause and failure modes are essentially the same thing. Both are causes of failure. The only difference is in the techniques that we use to identify them. With Root Cause Analysis (RCA) we are studying a failure event that has already occurred with the aim of preventing its re-occurrence. To do this we must understand all the contributing factors that led to the failure and identify the likely causes. We stop listing failure modes (causes) when it becomes possible to implement a suitable failure management policy – this is the “Root Cause”. RCA is concerned with a single failure event and is applied after the failure has occurred, so in this sense its scope is limited and it is a reactive approach.

The other technique that uses root causes/failure modes is the RCM approach. With RCM we try to identify all the likely causes of failure and their consequences for an asset or system and identify suitable failure management policies to address each failure mode. RCM is a proactive approach that is hopefully applied before the asset has failed with the objective being to mitigate or prevent the failure consequences. The output of RCM is a maintenance plan for the asset or system that covers all the likely failure modes.

Both approaches are extremely useful and quite complimentary.”

Steve Turner of OMCS added that he has a different understanding. “To me, if we are talking assets, there are failure modes which by definition from a dictionary, means the “manner for form” by which things fail. The word “cause” can mean the same thing. However when someone adds the word root to either failure mode or cause, they are meaning the failure mode or cause that was at the root of the problem. My understanding of causal relationships is that they are a continuum and they can have multiple trees. You can keep asking why forever and so you can never get to the root cause in reality…. there is no such thing. There are numbers of causes and events that end up causing failure. So with Dennis definition, his root cause is when we can put in a suitable failure management policy… Under his definition, Root Causes is a post failure thing. My definition is root cause can be established ahead of failures… RCA can be done in the future tense but it is not called by that name in futuristic studies.
I don’t want to add to the confusion, but some people use the term failure mechanism too and they say this term differs from failure mode. Maintenance is full of words that people use differently. You can see that Dennis has a different understanding to me… If I get into a technical conversation I often ask what they mean by the words they use so I understand the definitions being applied.”

Adhen Utomo, whom asked this question, realized that this company needs to decide and develop a dictionary related to maintenance since there is a lot confusion and debate for maintenance “word”. He agreed with Denis because “We have the same information from John Moubray, but there are a lot that might be we must search and digging for details of this issue in maintenance.”

Matt Thomnpson of Rio tinto added “The only thing I would like to add to the discussion is that athough failure modes ( from an equipment centric point of view) can often be thought of as causes not all causes can be thought of as failure modes. For example administrative causes or failures of procedures or management policies can be root causes of an RCA cause and effect chain but are not equipment or component failure modes.  Root cause and failure mode are classified as two separate things.”  

Matt had an example (however simple it is) to illustrate the differences:

EQUIPMENT:  e.g. furnace tube boiler

FAILURE: (what happened)  e.g. Catastrophic failure of the welded joint between the furnace tube and tube plate.

FAILURE MODE: (by definition is what the equipment or component failed from) e.g. Corrosion fatigue.

ROOT CAUSE/S: (by definition, what caused the failure mode to occur AND what can be changed to prevent re-occurrence. Remember there can be more than one!!)
e.g. Poor feed water treatment accelerated corrosion; Rapid firing, particularly from cold, increased thermal stress on the boiler; Over pressurization and temperature cycles.

If you liked this discussion, visit LinkedIn and join the RCM2 Group.