In an effort to state what is known and not known about hydrogen damage to steel in power boilers, this paper summarizes the varied conditions under which it has developed in 27 plants since 1938 and reviews pertinent research on the influence of chemical, mechanical, and metallurgical factors in producing this type of brittle failure. Hydrogen damage has occurred in many different locations in boilers of a great variety of designs operating at pressures from 450 to 2700 psi. It has been found only in the steel underlying local areas of corrosion, where hydrogen would have been produced at a greater rate than elsewhere. Metal temperatures in the range from 600 to 950 F suffice. Pure iron containing only 42 ppm of carbon is not damaged by hydrogen. Low-carbon steel is damaged less rapidly when the iron carbide has been spheroidized by prior heat-treatment, or when the oxygen content of the steel is relatively high. Low-alloy steels containing about 3 percent of chromium and small amounts of such elements as molybdenum, vanadium, and tungsten are highly resistant. Cold work increases the rate of damage by hydrogen.

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