Protection against local failure is one of the integral components in the design-by-analysis requirements in ASME BPVC Section VIII, Division 2. Of the methods offered by the ASME, the Local Strain Limit procedure outlined in 5.3.3.1 is the preferred calculation method. However, it has been found that relying on this procedure alone can lead to problems in the form of untenable utilization results if used on certain analyses with varied load paths.

The flange described in this study was calculated using design by analysis according to Part 5 of ASME BPVC Section VIII, Division 2. Elastic-plastic stress analysis method was used.  The flange was loaded with an initial bolt pre-tension and then with internal pressure. During the local failure calculation, an abnormal condition was encountered:  A large spike in the history curve of the ratio between plastic strain and limiting triaxial strain occurred, showing thousands of percent of utilization.

An investigation of these nodes found that with below yield stress, they had non-zero plastic strain. The non-zero plastic strain and low stress state were caused by the load sequence: first, the bolt pre-tension and then internal pressure. The flange, which first bent inward due to the pre-tension load, experienced outward bending after the internal pressure load was applied. This resulted in a low stress and non-zero plastic strain in certain areas, which then showed very high utilization under the local failure strain limit criterion.

This paper will discuss how this issue can be avoided by using the strain limit damage calculation procedure 5.3.3.2 outlined in ASME BPVC Section VIII, Division 2. It uses the principal stress, equivalent stress and change in accumulated equivalent plastic strain to calculate the utilization.


Local Failure Analysis of Bolted Flanges

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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