Chloride and Caustic Stress Corrosion Of Austenitic Stainless Steel in Hot Water and Steam^★

The various factors which affect transgranular stress corrosion of austenitic stainless steels in steam-hot water systems are discussed. The evidence indicates that complete solution of the problem cannot be guaranteed through control of the alloy composition and condition, or through control of temperature and stress level within practical limits. Control of such factors and attention to design can reduce stress-corrosion hazards, but complete elimination apparently requires treatment of the environment to render it noncorrosive. The most serious troubles are in the steam phase in areas where intermittent wetting and steaming can cause concentration of water solids. Stress corrosion from chlorides is shown to be dependent on oxygen content, and prevention of damage from this source may be obtained by limiting either the chloride level or the oxygen level. Stress corrosion from caustic solutions is not so well understood, but preliminary information indicates that the maintenance of a proper phosphatecaustic ratio may be a suitable preventive measure. 3.5.8