During pressure testing of a downhole plugging tool manufactured from a duplex stainless steel forging, a failure occurred that had not been observed in similar development projects. The failure was characterised by surface pinhole formation and cracking associated with a region of high plastic strain. Examination revealed that the defects were associated with areas of sigma -phase at the ferrite/austenite phase boundaries local to the centre of the 250 mm diameter forging. Estimation of the cooling rates of the forging during oil quenching showed that the centre region of the forging would not cool at a rate sufficient to exceed the critical cooling rate for sigma -phase formation. The material was shown to be capable of withstanding greater levels of plastic strain in regions where no sigma -phase existed. (C) 2001 Elsevier Science Ltd. All rights reserved.
- super duplex
- SIGMA-PHASE PRECIPITATION