Distribution law and statistical treatment method of fracture toughness in heat-affected zone of the girth weld

Crack tip opening displacement (CTOD) of the heat-affected zone of the 31.8 mm thick L485 pipeline steel girth welded joint was tested using the single edge notch tension (SENT) test method. The distribution fitting of 18 test results was carried out by using the mathematical statistical method and the distribution law of CTOD was determined by using A-D method and K-S method. The results show that, δ_m and δ_0.2 obey normal and lognormal distributions respectively, and the specific quantile CTOD values of them are obtained. Comparative analysis shows that CTOD value (δ_m and δ_0.2) determined by MOTE method is between 5% ~ 10% quantiles of probability distribution. The 10% quantile value (δ_m) of normal distribution and the 5% quantile value (δ_0.2) of lognormal distribution are consistent with the recommended practice of BS7910, indicating that the quantile method of CTOD value probability distribution function is a reasonable and feasible method to deal with discrete fracture toughness.