Mercury stress corrosion cracking of brass components can also occur in service due to contamination from broken thermometers. Recognition Stress corrosion cracking in brass is usually localised and, if ammonia has been involved, may be accompanied by black staining of the surrounding surface. The fracture surface of the crack may be stained or bright, according to whether the crack propagated slowly or rapidly. The cracks run roughly perpendicular to the direction of the tensile stress involved. Stress corrosion cracking in pipes that have been cold bent without a subsequent stress relief anneal occurs typically along the neutral axis of the bend.
Stress corrosion cracking due to operating stresses is transverse to the axis of the applied stress.
Examination of metallographic sections through cracked areas will usually show a markedly intergranular crack pattern in simple alpha brasses. In aluminium brass the cracking is transgranular and much branched and in admiralty brass either or both forms of cracking may be observed. The cracks look discontinuous in metallographic sections, as they divert above or below the plane of the section to pass round the alpha phase. It does show that the higher the copper content, the better the resistance to stress corrosion cracking. Similar results to these have been found by other researchers and are supported by practical experience.