Publications
| Title | | Authors |
|---|---|
| Fatigue strength of flawless gas transmission pipes: effect of mean pressure « back |
R Phnung-Ngoc, R Batisse, M Zarea, G Demofonti, G Mannucci and U Marewski |
| 12th PRCI/EPRG Joint Technical Meeting, Groningen, Holland, May 1999 | |
| The fatigue strength of large diameter pipelines subjected to internal pressure fluctuations is nowadays assessed almost exclusively on the basis of German standard DIN2413 (Steel pipes - Calculation of wall thickness subjected to internal pressure), which does not take into account the influence of mean stress. To extend knowledge on the fatigue life of flawless pipelines and specially on the influence of mean stress, EPRG launched a fatigue test program on 14 fuil scale vessels. Vessels were hydraulically tested until leak, except for some cases with no failure above 400,000 cycles. Test results were compared to the predictions of the DIN 2413 standard. The comparison was not satisfactory. Tests results were also interpreted taking into account the mean stress, using several criteria : the Gerber model, the Goodman model, and a multiaxial criterion. Conservative predictions are possible for the fatigue life of flawless pipes when the mean stress is taken into account. 1. INTRODUCTION The fatigue strength of flawless large diameter pipelines subjected to internal pressure fluctuations can nowadays be assessed on the basis of a specific Gerrnan standard, the DIN2413 (Steel pipes - Calculation of wall thickness subjected to internal pressure). The assessment according to this standard is based upon S-N curves, i.e. stress range vs. number of cycles to failure, obtained by results of full scale fatigue tests performed at a constant stress ratio R, which is about Zero (minimum stress during the fatigue tests about zero). The DIN 2413 does not explicitly take into account the mean stress value, but as R=O, the mean stress value is equal to half the stress range (i.e. the difference between maximum and minimum stress applied during the fatigue test). This direct relation between stress range and mean stress is not representative of the realistic operating conditions of gas transmission pipelines, i.e. low stress range with high mean stress. If the DIN 2413 is used to predict the actual fatigue life for such pipelines , the S-N curves can lead to nonconsemative predictions, due to the very low mean stress applied to establish this part of DIN 2413. In other | |
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