Small Punch Creep Testing of P91 Welded Joints

The present article describes preliminary investigations to show the suitability of the Small Punch testing technology for application as a lifetime prediction tool for metallic components operating at high temperatures. The lack of standardisation of this technique and doubts about the ability to correlate the test data with that obtained from conventional creep tests give strong arguments for further investigations in this direction, also in support of the recently launched Code of Practice for Small Punch Testing (CEN/WS 21) [1]. In particular this work is concerned with investigating the creep properties of P91 steel weldments and parent material at 600oC. Thin discs, 8mm in diameter and 0.5mm thick, were manufactured from different zones of a virgin to service-exposed welded P91 pipe. The first series of small-punch creep tests have been performed at 600oC under different loads following the Code of Practice and the results compared to the standard uniaxial creep tests results obtained for the parent material. Special attention has been paid to the experimental control conditions in particular exact temperature measurement, a known problem in the SP test implementation, and the effect of loading rate on the tests results. A first attempt is made to interpret the small punch test data for the different zones of the P91 welded joint and correlate this with the available standard creep data according to the procedure proposed in the Code of Practice which relates SP test load with uniaxial creep stress. ; JRC.F.4 - Nuclear design safety