Abstract
It has been known for some time that Monel is susceptible to intergranular stress corrosion cracking in fluosilicic acid. It was surprising, however, to find “K” Monel bolts breaking in transgranular fashion in hydrofluoric acid vapor. The diagnosis that these failures were stress corrosion cracking was confirmed by reproduction of the cracking in the laboratory. Several similar case histories are reviewed and a number of qualitative laboratory experiments on the stress corrosion cracking of Monel and some other high nickel alloys in hydrofluoric acid environments are described. The number and path of the cracks is influenced by composition, cold work, heat treatment, stress, time and conditions of exposure. Cracking is most prone to occur where corrosion rates are high, such as in moist, aerated vapor. This suggests that hydrogen may play a part in the cracking. Means of avoiding the cracking are discussed. 3.5.8
