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

Buried Polyethylene Pipe: An Excellent Choice for Water Service

Buried Polyethylene Pipe: An Excellent Choice for Water Service
Buried steel pipe is prone to pitting due to external (soil-side) corrosion and internal (water-side) corrosion and biofouling. Preventive and mitigative measures include periodic inspection, cleaning, chemical and biocide treatments, and repairs. A cost-effective alternative consists in replacing the buried steel pipe with a non-metallic pipe, in particular high density polyethylene (HDPE). This alternative, widely used for buried waterworks and gas distribution piping, has been used at several nuclear power plants for non-safety related piping. Through ASME Code Case N-755, an alternative is now available for safety-related Class 3 piping. The first industrial polymerization of the ethylene monomer CH2=CH2 into polyethylene (-CH2-CH2-)n dates back to the 1930’s. Today’s polyethylene pipe is designated by its ASTM D 3350 name, such as PE3408 where 3 stands for the cell density, 4 is its resistance to slow crack growth and 08 reflects its hydrostatic design stress at room temperature (allowable stress in service) of...
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What is the Future of ASME B31.3, Appendix P?

What is the Future of ASME B31.3, Appendix P?
Appendix P was written to introduce piping flexibility analysis rules that are more suitable for computer piping flexibility analysis, in contrast to the rules in the base Code which were written when piping analysis was done by hand calculations.  Most of the elements of Appendix P have been, or are proposed to be, added to the base Code.  So what does the future hold? The primary reason Appendix P was written was to introduce the concept of taking differences in operating stress states.  This is because there is an interaction between sustained and displacement loads with nonlinear systems.  Supports, for example, can be engaged in one operating condition, and not another, which effects the stress range of the system.  The base Code was written based on looking at stressed due to sustained loads and displacement loads separately.  Although commercial pipe stress software may take differences in operating conditions to determine the...
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Chuck Becht

Appendix P

Yes, at the last minute the deletion of Appendix P was implemented. I think all of Appendix P other than the alternative allowabl... Read More
Tuesday, 22 December 2015 14:08
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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...
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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
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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...
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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
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