Case Study: Root Cause on Seal Failure in Refinery

Semiconductor devices are almost always part of a larger, more complex piece of electronic equipment. These devices operate in concert with other circuit elements and are subject to system, subsystem and environmental influences. When equipment fails in the field or on the shop floor, technicians usually begin their evaluations with the unit's smallest, most easily replaceable module or subsystem. The subsystem is then sent to a lab, where technicians troubleshoot the problem to an individual component, which is then removed--often with less-than-controlled thermal, mechanical and electrical stresses--and submitted to a laboratory for analysis. Although this isn't the optimal failure analysis path, it is generally what actually happens.

Fatigue is a failure mode that every manufacturing plant will experience at some point and can become chronic if not solved. While understanding fatigue has advanced since its inception in the early 1800s, there are still some misunderstandings in manufacturing in solving these failures. A characteristic of fatigue failures is stress, which is typically below the yield strength of the material. This is what makes fatigue a silent killer.

Metal fatigue is the common name used to describe the unexpected failure of metal parts by progressive fracturing while in service. The article is a basic introduction to the mechanism of metal fatigue failure. An introduction into accepted theories is provided and relevant design practices to reduce metal fatigue are presented and explained.

Root Cause Analysis (RCA) is a useful tool for trouble shooting breakdowns and efficiently coming to a solution. I propose the following seven points for successful implementation of RCA that will naturally result in increased profits.

A fault tree is constructed starting with the final failure and progressively tracing each cause that led to the previous cause. This continues till the trail can be traced back no further. Each result of a cause must clearly flow from its predecessor (the one before it). If it is clear that a step is missing between causes it is added in and evidence looked for to support its presence. Below is a sample fault tree for the moral story of the kingdom lost because of a missing horseshoe nail.

Root Cause Analysis has the potential of CHANGING people, IF the leader of the investigation knows of this potential. Far from “just another problem-solving exercise,”the root cause analysis should SLOW PEOPLE DOWN to the extent that they can see the truth of the incident under inquiry, WHATEVER THE TRUTH MIGHT BE. This paper focuses on two parts of our human nature which are large obstacles to root cause discovery, i.e., our unwillingness to slow down, and our unwillingness to let go of certain basic assumptions about life. Warning: This paper is designed to challenge the way you think about Root Cause Analysis.