Stresses in piping systems subject to hydrogen detonation loading are complex. There are high-frequency localized shell-type stresses, such as hoop membrane, longitudinal through-wall bending and hoop through-wall bending due to asymmetric modes. There are low-frequency gross beam-type stresses, similar to those from a waterhammer, as the unbalanced forces excite the beam bending and bar wave modes in the piping system. From a code compliance standpoint, all the stresses need to be considered and categorized in terms of the type of failure that they can cause.
Part 1 developed a method to estimate the local shell stresses due to the detonation wave. This paper, Part 2, discusses an investigation into the global beam bending effects. It proposes a methodology for combining the beam and local shell effects, and evaluating the results in terms of complying with a typical piping code.
The gross stresses due to the propagating detonation wave can be evaluated using beam-finite element models and time-history analysis, similar to analyses for waterhammer. As with waterhammer, these stresses are typically considered “occasional” loads. However, the beam stresses can coincide with very high hoop or radial shell stresses, due to the high peak pressures involved, so that the simple comparison of using longitudinal stresses may not be an adequate design check. This paper recommends a combination of shell-equivalent stresses and beam-stress intensities that result in a conservative comparison, when compared to a full time-history analysis, but one which is not overly conservative.
With the exception of ASME Section III, Class 1, most U.S. piping codes do not provide rules for fatigue evaluation for loads other than displacement controlled loads. ASME B31.3 Appendix P provides guidance for pressure fluctuations, but the focus is primarily gross stress effects. The local effects from a detonation wave include both a “skin” stress effect on the inside surface and a through-wall bending effect due to the dynamic nature of the effects of the propagating wave. Both of these must be considered if the number of occurrences is significant. This paper proposes a method to consider these localized stresses that is patterned after the guidance in ASME Section III, NB-3600.