SCC susceptibility study of C-steel in cementitious environments relevant to the Supercontainer design: SSRT experiments under open circuit potential

An experimental campaign was initiated studying the SCC susceptibility of plain and welded P355 QL2 grade carbon steel (MIG/MAG, SAW and RPEB) exposed to artificial concrete pore water solutions (YCW, pH~13.6), simulating the supercontainer buffer environment, under anoxic conditions. The slow strain rate testing (SSRT) technique was used to investigate the effect of S2- (100 – 500 mg/L) and S2O32- (60 – 600 mg/L) on the SCC behaviour. This report summarizes and discusses the results of the SCC experiments carried out in the period 2009-2017. It was found that the addition of S2- and S2O32- had no discernible effect on the mechanical and ductility parameters, nor on the appearance of the fracture surface of carbon steel exposed to artificial concrete pore water under anoxic conditions. Most of the entire fracture surface of all specimens was found to consist of ductile dimples, which is an indication that failure primarily occurred due to a purely mechanical fracture. The presence of magnetite crystals was observed on the fracture surface of the samples tested in sulphide containing solutions. This indicates that some form of corrosion had occurred in these test solutions. Some specimens showed evidences of small and shallow secondary cracking in the necked down section immediately adjacent to the fracture. This was believed to be caused as a result of circumferential machining marks left on the specimen surface.