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

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...
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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...
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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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Changes In the 2012 Edition of ASME B31.3

In addition to the many clarifications, updated references to codes and standards, updates to basic allowable stresses, and added listed materials, there are several substantive changes to the 2012 Edition of ASME B31.3, Process Piping. These changes are: Category D Fluid Service The definition was revised to include piping with design minimum temperatures below -29⁰C (-20⁰F) if the cause of the lower temperature is from ambient conditions. Allowable Displacement Stress Range The allowable displacement stress range was limited to 60,000 psi (414 MPa) in the 2012 edition. High strength steels have higher yield and tensile strengths and thus higher allowable stresses. Therefore, they also have higher calculated allowable displacement stress ranges when calculated using the old formula. However, these materials have fatigue strengths similar to the more common steels, which is why the limit was added. Flexibility Stress Equation The axial stress was added to the flexibility stress equation. While...
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Byron Laird

Allowable Displacement Stress ...

Dear Don, Thanks for your article, very informative. Referring to your comment on the allowable displacement stress range. I can ... Read More
Wednesday, 11 September 2013 18:16
Don Frikken

MPa Stress table - response

The ASME B16.5 ratings are based on data supplied by the B&PV Code Section II Committee. In some cases, the MPa values are derived... Read More
Tuesday, 10 December 2013 11:31
Don Frikken

RE:withstand

I'm not familiar enough with ASME B&PV Code Section IX to know if there is an exception to the rule you describe. If the material ... Read More
Friday, 06 February 2015 09:17
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Piping Vibration Screening Rule

It is useful to have a screening rule for evaluation of piping vibration in order to determine if the vibration is potentially harmful (can lead to damage or fatigue failure) or if it is simply a nuisance and can be accepted without doing a more detailed assessment or anything to mitigate it. A very useful screening rule is provided in ASME OM-3 , “ Requirements for Preoperational and Initial Start-up Vibration Testing of Nuclear Power Plant Piping Systems;” however, it is first important to understand when it is appropriate to use this rule. It is not uncommon to have people use tools they are familiar with to address problems the tools are not suited for, yielding meaningless results. To understand where the OM-3 screening rule is applicable, it is useful to understand different categories of piping vibration. The first division is transient versus steady state. The screening rule is for...
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