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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.

ASME Section VIII, Division 2 Elastic Analysis Discussion: Collapse vs Ratcheting

ASME Section VIII, Division 2 Elastic Analysis Discussion: Collapse vs Ratcheting
  So, you think you know what load case combinations to use for your ASME Section VIII, Division 2, Part 5 analysis to satisfy Protection Against? Common sense says to follow to Code rules in Table 5.3 – but do you fully understand what that means? And, what loads should you use to satisfy Protection Against Failure From Cyclic Loading: Ratcheting? Are the same as for Plastic Collapse, or are they different? Over the past couple of weeks, I have had one particular issue come up several times with respect to elastic analysis to Part 5. There seems to be widespread misunderstanding about how to apply load cases to Protection Against Plastic Collapse and Protection Against Failure from Cyclic Loading – Ratcheting. So, I wanted to write this post to (hopefully) clear up some of this misunderstanding. Article 5.2, Protection Against Plastic Collapse, describes what design load cases and design load...
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Trevor Seipp

RE:ratcheting vs cycling

Ratcheting is a different failure mode from fatigue; which is why each failure mode is handled separately in Part 5. You raise a ... Read More
Tuesday, 12 January 2016 12:41
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API 579/ASME FFS-Based Software Delivers Efficient Evaluation of Brittle Fracture Resistance and Minimum Allowable Temperature

API 579/ASME FFS-Based Software Delivers Efficient Evaluation of Brittle Fracture Resistance and Minimum Allowable Temperature
Process vessels such as towers, drums and heat exchangers may be exposed to low temperatures as a part of normal operation or as the result of an upset condition. Carbon and low alloy steels typically used in process vessels undergo a transition from ductile to brittle behavior as temperature is reduced and are at increased risk of brittle fracture. To reduce this risk, the ASME Boiler & Pressure Vessel Code contains requirements for vessels and vessel components with respect to low temperature operation. While these rules are applicable to new construction, API 579-1/ASME-1 FFS Fitness-For-Service, hereafter referred to as FFS, uses the ASME Code rules as the basis for evaluating the brittle fracture resistance of existing vessels. Becht relies on its proprietary FFS software to provide clients with operating pressure limits as a function of decreasing vessel metal temperature. These limits can be used as part of the client’s process hazard...
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Performing an FEA in Section VIII, Division 1 to Qualify an Article U-2(g) Component

  While there are currently no explicit rules on how to perform a finite element analysis (FEA) if you are doing so in support of an ASME Section VIII, Division 1 vessel, there is good practice. Regarding rules, all you have is from Article U-2(g), which says: This Division of Section VIII does not contain rules to cover all details of design and construction. Where complete details are not given, it is intended that the Manufacturer, subject to the acceptance of the Inspector, shall provide details of design and construction which will be as safe as those provided by the rules of this Division. So, how exactly does an engineer perform an FEA, for which Section VIII, Division 1 has absolutely no rules, that is “as safe as” the rules otherwise provided in Section VIII, Division 1? Luckily, I’m not the first person to think about this. In fact, there is...
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Mark Warner, PE

Thank you

Thank you for this review. I have used this approach for conformable pressure vessels where you need FEA to address the abnormal g... Read More
Friday, 13 September 2013 01:57
Trevor Seipp

Re: Thanks for guidelines

Shino Ulahannan - thank you for your questions. "1. What does ASME say about allowable deformations for a pressure vessel or vacu... Read More
Saturday, 07 December 2013 01:04
Trevor Seipp

Deformation values

"can we take the % strain or corresponding deformation against allowable stress(S - as defined by part D) from the stress strain p... Read More
Monday, 09 December 2013 18:01
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Use of Fracture Mechanics for Fatigue Design

While fracture mechanics is used in fitness-for-service, FFS, for evaluation of crack like flaws that are detected and for evaluation of the potential for brittle fracture, it is also used in new design to evaluate fatigue life. The rules for high pressure vessels in Section VIII, Div 3 and ASME B31.3 Chapter X permit and sometimes require the use of fracture mechanics to evaluate the fatigue life of pressure vessels and piping. The fatigue evaluation starts with the smallest detectable flaw that could remain in the equipment after the specified examinations are performed. The growth of this postulated flaw is simulated via fracture mechanics until the flaw reaches the critical crack size or reaches a FAD failure. The allowable number of design cycles is then the lesser of: the number of cycles required to reach 20 years, to reach 1/4 critical crack size, or half the number to reach the critical...
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