Abstract
Failures by stress-corrosion cracking of marine boiler tubes are commonly the result of a concentrated caustic solution in contact with stressed boiler metal. Usually the concentration of the caustic results from leakage between seams and around rivets, or capillary action and subsequent evaporation.
A rare example of the same type of failure is one where no seams or crevices exist for concentrating the boiler solution by leakage; this is failure resulting from concentration of the boiler solution right on the steam generating surface of the boiler tube. Details of such a failure are discussed. In particular, it is shown that the attainment of the necessary caustic concentration and stress levels is feasible. It is pointed out that stress need not be as high as is commonly believed.
The mechanism of caustic cracking as understood today is reviewed; that is, electrochemical action aided by stress. In effect, this serves to include caustic cracking among such phenomena as the season-cracking of brass and the stress-corrosion cracking of stainless steel. It is commonly accepted that this type of failure is rare. That it does occurr suggests that some thought might be directed to preventing channelling by hot gases and to alternative chemical treatments which do not rely on caustic.
