This is the general basis behind what is known as the Hopper Diagram (because it resembles a grain hopper), shown below. Then, those linearized and classified stresses are compared to appropriate allowable stress limits. Therefore, the stresses as calculated in the FEA in specific locations, called Stress Classification Lines (SCLs), are further linearized and classified. Because not all stresses will contribute to plastic collapse or ratcheting, a stress-at-a-point limit is not meaningful. In demonstrating Protection Against Plastic Collapse and Protection Against Failure From Cyclic Loading: Ratcheting, one of the methods provided in Part 5 is a linear-elastic method. What is stress linearization and categorization?
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For Protection Against Plastic Collapse, the elastic method uses an Allowable Stress Design (ASD) approach, whereas the elastic-plastic method uses a Load and Resistance Factored Design (LRFD) approach.
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In general, these options involve an elastic method and an elastic-plastic method.
ASME SECTION 8 PDF HOW TO
Protection Against Failure From Cyclic Loadingįor each failure mode, the analyst is presented with multiple options of how to perform the analysis that would demonstrate that the specific failure mode has been protected against.
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ASME SECTION 8 PDF CODE
The Code writers (who, by the way are all volunteers) have spelled out four failure modes that require attention: The entire approach of this Code (which has changed substantially from the pre-2007 Editions) is centered on the philosophy of Protection Against Failure Modes. It provides detailed rules for performing analyses. What is Design By Analysis?ĭesign By Analysis, as described in ASME Section VIII, Division 2, Part 5 is a methodical approach for demonstrating the adequacy of a pressure vessel component design. In ASME Section VIII, Division 2, you can move between Part 4 (Design By Rules) and Part 5 (Design By Analysis) a little more easily, subject to the regulations in the locale where the pressure vessel will be located. In ASME Section VIII, Division 1, that is covered in Article U-2(g), which I have discussed previously. However, there are some situations where the rules don’t cover a specific design geometry or load that may necessitate the use of FEA. So, wherever possible, I would recommend that you follow those rules. 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. The short answer here is that for most situations, you probably should not be using FEA to design your pressure vessel. When do I have to use FEA in my pressure vessel design? We generated several questions, and so I decided to post this in a Question & Answer format. I was recently discussing with another blogger regarding some distinctive aspects of performing Design By Analysis for pressure vessels. What is it about FEA for pressure vessels that makes it unique? 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. Piping Pressure Vessels Reliability Improvement