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Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.

Equipment Nozzle Loads

Equipment Nozzle Loads
by Greg Hollinger and George Antaki One of the qualification requirements for a piping system is to keep the loads imparted by the piping on equipment nozzles within certain allowable limits. These loads consist of sets of three forces and three moments, for the various load combinations. There are basically two types of nozzle load limits: (1) nozzle loads applied to active equipment, and (2) nozzle loads applied to passive equipment. Active Equipment Nozzle Loads Active mechanical equipment consist of equipment with moving parts, such as pumps, compressors, and fans. The pipe nozzle load limits are developed by the equipment manufacturer and are intended to prevent malfunction, such as shaft misalignment, or distortion of the casing that could impede the movement of impellers. These limits are typically based on actual testing of the equipment, and not on analysis. Some standards have published standard pump nozzle loads, but these are only valid for...
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Shaft Fatigue Failures – Part I

Shaft Fatigue Failures – Part I
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...
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Shaft Fatigue Failures – Part II

Shaft Fatigue Failures – Part II
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...
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Process Centrifugal Compressor Oil Seals

Process Centrifugal Compressor Oil Seals
Ingersoll Rand Cone Oil Seals Compressor process shaft end seals are designed to seal the rotating assembly in the stationary compressor case to prevent the process gas in the compressor from escaping to the atmosphere and to prevent the atmosphere from getting into the process gas.   Shaft end oil seals, as compared to the relatively new dry gas seals, have been in the machinery world since the inception of centrifugal compressors.  A comparison of advantages and disadvantages for each type of compressor shaft end seal (gas or oil) will not be covered in this article.  It is safe to say that today’s trend is to purchase new centrifugal compressors with dry gas seals, and where feasible, to retrofit existing oil seals with dry gas seals. Purpose The purpose of this article is to outline the basic components of a compressor oil seal and support system, with a brief description on how...
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