Becht Engineering Blog

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”. While...

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 the...

Gerrit Buchheim, Manager of the Pono Division of Becht Engineering, has developed a practical and simple-to-use approach to prioritizing the inspection and replacement of equipment in High Temperature Hydrogen Attack ( HTHA ) service.  This approach utilizes the existing and accepted “Nelson Curve”, but adapts it to better fit the realized operating conditions at an individual facility, based on several factors that have not been previously considered. Background Historically, the industry has used experienced-based curves (API 941 Nelson Curves) in the selection of materials as well as evaluating existing in-service equipment.   These curves have served the industry well to now, but in the past 5 years, there have been several notable cases of HTHA that fall below the established curves and there is still a sizeable base of C-0.5 Mo equipment operating above the carbon steel curve.  Therefore, industry needed a more realistic method for evaluating existing equipment in potential HTHA...

In 2008, Becht Engineering was awarded a project by the Materials Technology Institute (MTI) to develop an inspection guideline document and software tool for the collection and analysis of inspection data for piping, piping components and pressure vessels. Dr. Eileen Chant , as project manager, collaborated with Bob Sims of Becht, Dr. Mark Stone of Sonomatic Ltd., the ultrasonic inspection technology company affiliated with Becht, and Dr. William Meeker, a statistics expert at Iowa State University. MTI was founded in 1977 and is a not-for-profit technology development organization serving the needs of its members in key processing industries such as Refining, Mining, Energy production, Chemical production and other manufacturing industries for which safe and reliable fluid storage is critical. A typical refinery or chemical plant may have hundreds of miles of piping and hundreds of pressure vessels that require regular inspection to permit their safe and reliable operation. The inspection document...