A microstructural investigation on the cracking of the Muhleberg reactor primary pipe "CH1"
The cracking of a primary pipe of the Muhleberg reactor was investigated by means of optical microscopy, scanning electron microscopy and electron probe microanalysis. The circumferential crack, extending almost 360 and 2-6 mm deep, started to propagate from the sharp edge of the counterbore. Since the crack initiation occurred at 45 circumferential location in the heat-affected zone near the weld, where intergranular precipitation of carbides has been found, it is concluded that the crack initiated primarily by stress-corrosion, as a consequence of residual stresses and weld sensitisation. Taking into account the fact that at other circumferential locations the crack was found to be outside the heat affected zone, it cannot be excluded that the propagation of the circumferential crack might be due also to fatigue corrosion. However, given the fact that the deepest cracking occurs in the heat- affected zone, the stress-corrosion mechanism seems to be predominant. The corrosive environment was likely to be originated or enhanced by sulphide ions, formed by dissolution of manganese sulphide inclusions in the crevices, as found in previous investigations on low alloyed steels.
Bibliographic Reference: EUR 12888 EN (1990) 40 pp., MF, ECU 4, blow-up copy ECU 5
Record Number: 199011343 / Last updated on: 1994-12-01
Original language: en
Available languages: en