Additional Information - Posters # 1998 Gothenburg
This paper presents experimental evidences and experiences obta~nedfrom the use of the so-called Miner's rule for determination of lifetime expectancies of plastic pipes subjected to varying testing conditions, i.e. altering temperatures and pressures. Results obtained from some unique long-term pressure tests of PE, PP, PB and PEX (Stage 111) performed at constant temperatures are presented as well as results obtained from cycling tests for validation of Miner's rule. The latter results show that Miner's rule is overestimating the lifetime in many cases for the investigated materials. In one case was just 57% of the lifetime observed compared to the one predicted with Miner's rule. This indicates that much too optimistic results may be predicted with Miner's rule if no care is taken in validating this method before usage. However, more work is needed in order to definitely confirm this conclusion. The paper also gives a background and an introduction to Miner's rule according to ISODIS 13760 and the Standard Extrapolation Method (SEM) according to ISOrTR 9080. Where the SEM is used to support the Miner's rule calculations of the lifetime at altering service conditions.