Brent St. Blanc

Many companies and organizations have been on the reliability journey for a number of years, while others are just beginning.  There are many elements of a solid reliability program – establishing a reliability centered culture, tracking key metrics, bad actor elimination programs and establishing equipment reliability plans – to name a few.  But, one key element to a solid reliability program, and one that is very important to improving unit reliability metrics, is root cause failure analysis (RCFA). Historically, various methods have been used over time to assist in RCFA – Why Tree Analysis, 5-Whys, and Fishbone Diagrams.  However, one common tool to facilitate and document the RCFA is a Cause Map, or Cause and Effect Diagram.  Cause Mapping is a very flexible platform, which allows utilization for any type of failure investigation, regardless of equipment type, industry, or complexity.  Cause Mapping starts with a primary effect – where the...

Many years ago when I first started my career in a rotating equipment maintenance organization, I was spending the day with a senior metallurgist, which was part of my orientation process as a new technical employee.  He was well known to not have the best “bedside manner” and it was clear he was not thrilled to have a young mechanical engineer by his side for the day.  As I walked into the materials lab, looking for something to start a conversation, I picked up a small broken ANSI pump shaft and asked if he knew why this shaft had failed?  His response I vividly remember to this day – he said, “Son, I have not analyzed that failure yet, but if it is a shaft out of a piece of rotating equipment and is broken into two pieces, there is about a 90% chance that it is a fatigue failure”....

Note:  This blog is a continuation from the previous article from Becht Engineering, “Shaft Fatigue Failures – Part I”.  It is suggested that the reader review “Shaft Fatigue Failures - Part I” before proceeding with this article.   Click Here to view Part I. Before getting into the calculation methods, first a quick refresher on high cycle fatigue.  High cycle fatigue failures are typically acknowledged to be fatigue failures resulting from alternating loading cycles in excess of 10 6 cycles.    While that may sound like a large number, in high speed rotating machinery, one million cycles will occur in hours.  For high cycle fatigue, the fatigue test data is often reported in the form of alternating stress vs number of cycles (S-N, or Stress-Life method).  Fortunately, many of the common shaft and rotor alloys exhibit a fatigue strength “endurance limit” at about 10 6 – 10 7 cycles, beyond which...