2013

Sipilä, Konsta; Arilahti, Esko; Lehtikuusi, Taru; Saario, Timo; Varis, Päivi

A Japanese research group reported in 2008 susceptibility to stress corrosion cracking of oxygen free phosphorous doped copper (CuOFP) in sulphide containing sea water at T = 80°C and under uniaxial slow dynamical loading conditions. More evidence for stress corrosion cracking has not been found under multiaxial constant loading conditions in sulphide containing groundwater at T = 25°C. Indications of possible sulphur ingress to CuOFP grain boundaries from sulphide containing groundwater were found, which initiated further studies on the possibility of grain boundary embrittlement through such ingress. Further studies were conducted in order to clarify the effect of sulphide exposure on the mechanical behaviour of CuOFP. Tensile and creep tests were performed with specimens exposed to sulphide and reference specimens. In the studies presented in this paper only small con-centrations or no sulphur at all was found on fracture surfaces, in contradiction with earlier studies with precracked compact tension (CT) specimens under constant load. It is suggested that the high concentrations found earlier may have been caused by the method of opening up the fracture surfaces (i.e. post-exposure fatigue in air) and thus be an artefact. The tensile tests performed after the exposure to sulphide containing ground-water indicate a degrading influence of the exposure on mechanical properties of CuOFP. The result is based on adequate number of specimens and a standard test practise. The creep tests performed within the studies presented in this paper seem to indicate a minor degrading influence of the exposure to sulphide containing groundwater. However, when compared with all the publicly available creep data on CuOFP from different heats and laboratories the current finding is still within the scatter band.