Thermal fatigue of pipes induced by fluid temperature change. (13) Relationship between failure probability and thermal loading conditions

Failure probability and crack initiation probability of a pipe is greatly affected by the stress caused by thermal fluctuation. The stress is affected by the temperature difference and with a hot-spot or a cold-spot. Crack initiates just only in the case of 150degC temperature difference with a hot-spot. If an initial crack exists, cumulative failure probability as of 10 years operation is 0.8 and 6.3 x 10^-3 in the case of 75degC and 35degC temperature difference without hot-spot. In order to reduce the failure probability, it is necessary to reduce the temperature difference. In addition, eliminating the initial crack is effective to reduce the failure probability. (author)