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.
Becht Engineering staff are experts in piping, and include former chairman of various ASME piping committees, including ASME B31.3. Becht Engineering performs detailed design for complex piping systems including very high temperature and pressure systems such as piping for FCC flue gas expanders and high pressure LDPE systems, as well as design, a...nalysis, troubleshooting and fitness for service evaluation of piping. More

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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Tom Vowell

ASME vs EJMA STRESS VALUES

Hi. I just had a bellows mfr send me 2 sets of calcs, EJMA and ASME for a 16" 316ss bellows. When he sent the EJMA calcs I noticed... Read More
Wednesday, 16 October 2013 00:07
Chuck Becht

Response to Stress Question

Sa is the allowable stress from the applicable code. Perhaps there was confusion over which code was applicable. For example, wa... Read More
Wednesday, 16 October 2013 16:10
Chuck Becht

examination

That is the minimum required exam for any metallic bellows to be used in ASME B31.3 piping. There is not a lesser inspection opti... Read More
Thursday, 04 February 2016 12:03
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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

Hydrotest Pressure

The leak test requirements in Chapter IX are more stringent than the base code. While the test pressure is generally the same, it... Read More
Monday, 14 April 2014 15:57
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
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
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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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When Should Category M Fluid Service be Selected for ASME B31.3 Piping Systems

ASME B31.3 provides rules for Category M Fluid Service in Chapter VIII of the Code. These rules are designed to provide additional measures of leak tightness. For example, special precautions to prevent leakage past valve stems are included and a sensitive leak test designed to find even very small leaks in the system is required. The Code requires that the owner decide if a piping system is in Category M Fluid Service. Note that it is Category M Fluid Service and not Category M fluids, as it is not simply the fluid, but also the conditions of installation that are considered in making the designation. The owner is guided in the classification for the piping system by the definition of Category M Fluid Service in Chapter I of ASME B31.3. Further, a guide to the application of these rules is provided in ASME B31.3, Appendix M, which contains a flow chart...
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Chuck Becht

example

An example of a fluid that would be considered Category M if the other conditions are satisfied would be Phosgene, or MIC
Thursday, 04 February 2016 12:11
Chuck Becht

ASME Code Scope

The ASME B31.3 code is essentially for creating a safe pressure boundary. It does not provide guidance for sizing pipe or calcula... Read More
Sunday, 14 December 2014 18:26
Chuck Becht

RE:Should be a H2S piping cons...

You need to consider the conditions of the installation, and the hazard that would be caused by a small leak. For example, if it ... Read More
Saturday, 07 March 2015 08:20
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