Application of statistical acceptance by measurement in yield strength tests of tubes for nuclear power plant steam generators

The possibility was tested of using the principle of statistic acceptance for selective checks of seamless tubes, cold drawn from steel 08Kh18N10T for steam generators of nuclear power plants. The results were analyzed of the tests of yield strength Rp 0.2 at 350 degC over a period of 10 months. 18,731 samples from 216 pipe groups were tested. It was concluded from the test of agreement of empirical and theoretical distributions that the technological process could be considered to be highly stabilized and the conditions for statistic acceptance by measurement satisfied. The technique specified in ISO 3951 was applied in the selective yield strength test. The individual steps of the acceptance are described and the values of selection characteristics are listed. A model application of the statistical acceptance by measurement showed high efficiency of the test method proposed, its considerable sensitivity to distribution normality, and mainly, the capability of revealing groups with as little as one tube of unsatisfactory quality, this at significant savings in the cost of yield strength testing. (J.B.). 2 tabs., 6 refs