ASME VIII-2 Stress Classifications and Limits
File: File:PVE-4495
Last Updated: Aug 31, 2010
By: DRV
For pressure equipment FEA is typically completed in accordance with ASME VIII-2 Part 5 Design by Analysis. The user creates a solid model, applies an appropriate mesh, material properties, loads and boundary conditions. The FEA then provides corresponding displacement and stress results. The difficult part however is analyzing these results to ensure a safe design or code compliance.
 A Stress Plot of a Valve under pressure |
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The ASME code provides guidance and acceptance criteria for FEA results. It categorizes stresses into two categories based on the failure mode they are expected to induce and provides allowable stress limits for each. The first "primary stresses" are stresses located in areas which plastic collapse is expected to occur if loadings exceed design, such as a pipe under internal pressure. The second "secondary stresses" are caused by geometrical discontinuities and are in addition to primary stresses. These stresses are in proportion with primary stresses until the yield point. After reaching yield secondary stress regions are expected to be self-limiting, supported by adjacent material, and result in localized yielding opposed to plastic collapse. The hub of a flange of the valve below is a good example of this. |
Primary stresses that exceed the yield limit by some margin will result in failure and as such are limited to 1X the allowable ASME stress limit.
Pressure Vessel Engineering has over 8 years of experience analyzing components to the rules of ASME VIII-2 using FEA. A complete engineering report is available below representing a typical analysis and report done in compliance with ASME VIII-2.
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