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

When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

There has been a fair amount of confusion as to when the rules for severe cyclic conditions in ASME B31.3 should be used, and the rules themselves can be somewhat confusing to apply.  The definition as to when the rules of severe cyclic apply is in the 300.2, Definitions.  It states that it is severe cyclic conditions are: • Conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5), and • the equivalent number of cycles (N in para. 302.3.5) exceeds 7000; • or other conditions that the designer determines will produce an equivalent effect. So, severe cyclic conditions applies to piping systems with a lot of displacement cycles, which are rare in most process plants, and the calculated displacement stress is close to the allowable displacement stress.  For these piping systems, fatigue is a greater concern. Following the rules...
Continue reading
21
  22823 Hits
  12 Comments
Recent Comments
Chuck Becht

answer to question

There is an new Appendix being voted on for high cycle fatigue, which is suitable for use with FPSO's. However, I believe it's fo... Read More
Wednesday, 01 October 2014 16:25
Chuck Becht

severe cyclic

Severe cyclic applies when the number of cycles exceeds 7000 so the f factor will be 1 or lower, not 1.2. The 0.8 factor is a c... Read More
Thursday, 04 February 2016 12:01
Chuck Becht

Response to recip piping comme...

The B31.3 code has changed the criteria to a more subjective one, and I will address that in a future blog. But it does not speci... Read More
Monday, 09 October 2017 09:34
22823 Hits
12 Comments

What is Bellows Pressure Thrust?

Pressure thrust is present in all pressurized piping systems. It is simply the gage pressure times the inside area of the pipe. It acts at changes in direction, such as elbows, and at changes in pipe cross section, such as reducers. Pressure thrust is normally carried as an axial load by the pipe. However, inclusion of a bellows expansion joint, which is not intended to carry such axial loads, removes the normal means of resisting the pressure thrust.  Therefore, other means, such as pipe anchors and hardware on the bellows such as tie rods, is required to carry the pressure thrust load. The pressure thrust is the gage pressure times the area within the mean diameter (Dm) of a metallic bellows expansion joint. It can be helpful in system design to understand where the forces actually occur.  Some pipe stress software use the simplifying assumption in the analysis that the force...
Continue reading
22
  19438 Hits
  5 Comments
Tags:
Recent Comments
Chuck Becht

RE:Question

With a bellows fillet welded to the OD of a pipe, there will be pressure acting on the end of the pipe, within the bellows. The p... Read More
Thursday, 03 December 2015 10:56
19438 Hits
5 Comments

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...
Continue reading
7
  10769 Hits
  12 Comments
Recent Comments
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
10769 Hits
12 Comments

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...
Continue reading
13
  13041 Hits
  11 Comments
Recent Comments
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
13041 Hits
11 Comments