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

Basics of Design By Analysis in ASME Section VIII, Division 2

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How hard can it be?  I’ve heard from several (unnamed) analysts that because they have access to an FEA program and have successfully applied FEA in other fields, that FEA for pressure vessels should be a snap.  What is it about FEA for pressure vessels that makes it unique? I was recently discussing with another blogger regarding some distinctive aspects of performing Design By Analysis for pressure vessels.  We generated several questions, and so I decided to post this in a Question & Answer format. When do I have to use FEA in my pressure vessel design? The short answer here is that for most situations, you probably should not be using FEA to design your pressure vessel.  The rules for designing pressure vessels in ASME Section VIII, Division 1 and ASME Section VIII, Division 2 have a long history of successful application.  So, wherever possible, I would recommend that you...
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Reducing Loss of Primary Containment (LOPC's) in a Refinery

cover-LOPCs
Reducing Loss of Primary Containment (LOPC's) or commonly referred to as “leaks” in a refinery is a key factor to improve reliability.  Historically, most refiners reduced the high consequence leaks to avoid major incidents; however, lower consequence related leaks were not given high priority.  Today high reliability is required, and reduction of all leaks is desired due to greater legal and regulatory oversight of the industry.  Approximately 90% of the leaks occur in piping systems.  These leaks typically fall into 3 categories; internal corrosion, flange leaks and external corrosion.  Many refiners have programs in place for internal corrosion and programs for flanged joints; however, many lack comprehensive programs for external corrosion. To fully reduce LOPCs a comprehensive internal and external corrosion management system is necessary. Background Many refineries have had Mechanical Integrity related audits performed during the last decade.  These audits have found many areas for improvements and programs were initiated...
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Elastic Follow-up Can Result in Failures in Systems that Comply with Piping Code Rules

piping_results_elastic_followup1 Cracking In Reduced Diameter Region Caused By Elastic Follow-up
The analysis procedures in the Code essentially assume that the strain range in the system can be determined from an elastic analysis. That is, strains are proportional to elastically calculated stresses. The stress range is limited to less than two times the yield stress, in part to achieve this. However, in some systems, strain concentration or elastic follow-up occurs. A typical concern in refinery systems is hot walled sections in otherwise refractory lined piping systems, where thermal expansion loading has resulted in cracking in the hot walled section although it complied with the basic code acceptance criteria. As an example, consider a cantilevered pipe with a portion adjacent to the fixed end constructed with a reduced-diameter or -thickness pipe or lower-yield-strength material that has the free end laterally displaced. The elastic analysis assumes that strains will be distributed in the system in accordance with the elastic stiffnesses. However, consider what happens...
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Fluid Catalytic Cracking (FCC) Transfer Line Flexibility - Analysis and Design Considerations

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FCC’s are complex units - and the design of their transfer lines has some unique considerations.   While many of the lines are refractory lined to permit construction with carbon steel piping, some sections are hot walled, at temperatures well into the creep range, for the purpose of balancing thermal expansion or, in the case of piping between the final catalyst separations device and flue gas expanders, to prevent dislodged chunks of refractory from being drawn into and damaging the expander.  Below are some critical considerations: The stiffness of the piping and resultant loads on equipment are affected by the presence of internal refractory . The composite action of the steel pipe and refractory needs to be considered.  Note that this is not simply including the refractory as a monolithic element, since the refractory will have shrinkage cracks.  There is a paper by T Chadda on an approach that can be...
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