Small punch creep testing of P92 steel and weld for inter-laboratory comparison and standardization

The small punch creep (SPC) test is a miniature technique that can provide information on creep properties from in service materials or on local material properties such as heat affected zones in weldments. The code of practice (CoP) for the small punch testing technique is currently being transformed into an EN standard. To qualify the selected test specifications and to quantify inter-laboratory data scatter a round-robin was launched for the standardization effort. SPC and reference uniaxial creep tests are performed on P92 steel at temperatures of 600, 625 and 650°C. In parallel a testing programme on P92 welds have been started in the European Creep Collaborative Committee (ECCC). In this paper the initial test results of both these testing programmes are assessed and compared. The initial results show that the SPC time to rupture data scatter is reasonable and that inter-laboratory results are comparable at all specified force levels and temperatures. From the weld tests on specimens targeted to be positioned in different heat affected zones it can be shown that rupture times are indeed affected but no clear reduction in strength can be determined for the short term SPC test. It is clear that the bi-axial stress state and the different stress evolution during the SPC test in comparison to a uniaxial creep test is a challenge when attempting to formulate load to stress transformation equations. Robust estimates on the uniaxial stresses for P92 are acquired by both new approaches and by isothermal determination of force over stress ratios using the classical CoP methodology. This work aims to aid the development of the new standard and to highlight the usability of the method for remaining life or life extension assessments.

HOLMSTROM Bjorn;  DYMACEK Petr;  JEFFS Spencer;  LANCASTER R.J.;  HURST Roger Christopher;  TONTI Andrea;  POGGIO E;  VACCIERI E; 

2017-11-02

Steel Institute VDEh

JRC103347

978-3-514-00832-8,   

https://eccc2017.com/home.html,    https://publications.jrc.ec.europa.eu/repository/handle/JRC103347,