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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.

The Difference Between ASME B31.3 Appendix X and EJMA Fatigue Curves for Bellows?

The Difference Between ASME B31.3 Appendix X and EJMA Fatigue Curves for Bellows?
Bellows vendors will often quote two different cycle lives for their bellows. One is in accordance with ASME B31.3, Appendix X. The other is in accordance with the Standards of The Expansion Joint Manufacturers Association. The latter provides a significantly higher cycle life. The EJMA bellows fatigue curve is a best fit curve based on data that was available, so it provides an expected average cycle life. The ASME curve was developed also using bellows fatigue data, but it provides design margins consistent with ASME pressure equipment codes. Historically, designers have put large factors of safety on the number of design cycles for bellows, which was in part justified since there was no design margin in the EJMA fatigue curve. This would result in a margin of safety entirely dependent upon the designer, and could vary from large, to none. This was not a satisfactory condition for an ASME Code, so...
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Chuck Becht

EJMA Column Squirm

The 2.25 factor cited in B31.3 is the same factor that is cited in EJMA, so use of the EJMA equations for column squirm are accept... Read More
Monday, 07 May 2018 16:58
Chuck Becht

examination

There are changes proposed for the 2016 edition that would drop the appendix X fatigue curve and use new EJMA fatigue curves. The... Read More
Thursday, 04 February 2016 12:07
Chuck Becht

validation testing

I have not reviewed the latest EJMA standard so cannot comment.
Thursday, 04 February 2016 12:08
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When Should the High Pressure Rules in Chapter IX of ASME B31.3 be Used?

The simple answer to this question is they should be used when the owner selects the use of these rules for a particular piping system. Note that the definition of High-Pressure Fluid Service simply requires that the owner specify use of Chapter IX. However, it is probably useful to understand why such a selection may be made. Some guidance is provided in K300 (a), which states that "High pressure is considered to be pressure in excess of that allowed by the ASME B16.5 PN 420 (Class 2500) rating for the specified design temperature and material group." This is not a requirement, and the base Code may be satisfactorily used at pressures higher than ASME B16.5, PN 420 (Class 2500). However, the base Code rules become increasingly conservative and, in fact, impossible to use as the pressure approaches the allowable stress (including quality factors). When this occurs, the wall thickness of straight...
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Chuck Becht

NDE Requirements

See K302.2.1 for unlisted components and K326.3 for listed components. The NDE requirements are for the fabricated piping system ... Read More
Monday, 07 May 2018 14:35
Chuck Becht

RE:Thickness equations chapter...

The equations in B31.3 are based on those developed for ASME Section VIII, Division 3 (Div. 3), the High Pressure Vessel Code. Ho... Read More
Monday, 07 December 2015 07:56
Chuck Becht

RE:Hydrotes Pressure

Because of the code wording which exempts listed components from code requirements (including testing) there is at this time a con... Read More
Monday, 07 December 2015 08:01
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Leadership

I was asked to participate in an engineering career development panel session at the 2013 ASME Pressure Vessel and Piping Conference which was held in Paris, France. I elected to talk about what engineers can do to improve their leadership skills. I am including some of the introductory material in this blog; the full presentation can be downloaded as a pdf here. I thought it best to clearly define what a leader is. It is simply a person that people follow. This is separate from the definition of a manager, which is an appointed position whose role is to plan, organize and coordinate the work. Generally, the most effective managers are also leaders. And generally, an organization needs leaders to achieve its potential and grow. If you wish to be a manager, and are in an organization that prefers to select people with leadership skills as managers, then you should develop...
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Why is Velocity a Good Indicator of Pipe Stress Due to Vibration?

There are three characteristics of motion which are all related by the natural frequency of vibration for steady state harmonic vibration: displacement, velocity and acceleration. Of these, which is the best indicator for cyclic stress (or strain) which in turn is related to fatigue damage? As it turns out, it is velocity. One may think that is should be displacement since stress is proportional to displacement, but the same displacement can result in different stresses in different piping systems. The same displacement will generally cause a higher stress in a stiffer piping system than in a more flexible piping system. You can understand why velocity is the best indicator if you consider energy concepts. Vibration is a transfer between kinetic and potential energy. The maximum kinetic energy is at the point with maximum velocity, which is when the displacement is zero (that is also where the acceleration zero, it is switching...
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