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Use of the austenitic stainless steels permitted increases in steam temperature in the power industry from 1000 F up to 1200 F. Problems of cracking at welded joints in Type 347 heavy-wall steam piping used at 1050 to 1100 F (566 to 593 C) resulted in changing to Types 304 and 316 steels for pipe. Creep failures in Type 321 superheater tubing have been resolved by use of the Type 321H material. Residual elements had no part in the problems with Types 347 and 321. A study made by the Edison Electric Institute shows that as pressure, temperature, and size of units have increased, operating availability has decreased. The result is a downward trend to 1000 to 1050 F (538 to 566 C) in temperature of new designs. Failures due to corrosion pitting of stainless steel condenser tubes were reported in several plants in 1965. Type 304 tubing used in a few plants as a replacement material in feedwater heaters has a good record. Research to improve the strength of Type 304 shows the beneficial effect of 0.07 to 0.15 per cent nitrogen in improving the rupture strength at 1200 F (649 C). A review of the use of austenitic stainless steels and the experience with the materials shows that the residual elements present in commercial materials have no effect on the use of the austenitic stainless steels in the power industry.
residual elements, austenitic stainless steels, stainless steels, electric power generation, high temperature, pipe, superheaters, condensers (liquefiers), feedwater heaters, weldments, corrosion
Rohrig, I. A.
Materials engineerPersonal member ASTM, The Detroit Edison Co., Detroit, Mich.