The dissolved oxygen content of water influences the susceptibility of austenitic stainless steels and reactor pressure vessel steels to environment assisted cracking by raising the electrochemical potential. The relevance of this fact to the integrity of welded stainless steel constructions, deaerator vessels and reactor pressure vessels steels is discussed. In particulal, the use of slow strain rate test procedures involving applied electrochemical potential control is discussed as a means of assessing the susceptibility to cracking of materials in a range of aqueous environments.