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

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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Five Keys to a Cost-Effective Repair/Modification Package for Tanks-Vessels-Piping

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: Process : Does the repair change the process chemistries, physics (fluid phase), and thermo-hydraulics (flow rates, pressures, temperatures)? Does the modification change the control room indications and the operating envelopes? Material : Are the selected metallic materials (base metal and welds) and non-metallic materials (gaskets, packings, etc.) compatible with the existing materials, with the environment, and with the service, for the design life of the repair? Is the material compliant with (a) the material specification (ASTM or ASME II), (b) the supplementary Code requirements, and (c) the supplementary plant-specific requirements? Will the material be procured from an approved supplier; does it require supplementary Quality Controls? ASME Code design : Does the modification alter the system layout? If yes, has the layout been checked for good practice and consistency with the process design (item 1 above)? Are the loads and load combinations well defined and categorized as Service Levels A, B,...
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12 Checks When Qualifying Piping Systems in Nuclear Applications

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The analysis and qualification of piping systems in nuclear power plants involves more than meeting Code stress limits. Generally, a piping system is qualified if the following criteria have been met. These various qualification criteria are typically specified in the plant FSAR, the plant design procedures, or the ASME Code. Pressure design in accordance with the design Code. This check will govern the schedule of pipes, the thickness of tubing, the schedule and pressure class of fittings, the reinforcement of openings and branch connections, the pressure rating of valves, the pressure class of flanges, and the pressure design of specialty fittings. ASME Code stress limits . This check will verify that the Code stress equations for the load combinations corresponding to Test, Design, and Service Levels A, B, C, and D loadings have been met. NRC Standard Review Plan (SRP) Section 3.6 stress limits for the postulation of high energy line...
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