The influence of minor constituents on the OXIDATION OF A HIGH ALLOY STEEL

Centrifugally cast reformer tubes in a nominal 25 Cr 20 Ni austenitic stainless steel have cracked when used to carry out the reforming of butane‐steam mixtures to hydrogen—carbon monoxide—carbon dioxide mixtures, with firing temperature approaching 1,000°C, in reforming plants. Surface oxidation on the firing side, producing notching, has led to cracks which have been encouraged to propagate by chains of sigma phase. Machining off the unsound metal after casting has presented a good stable austenitic surface to the fire. Adjustments to the relative amounts of Cr and Ni, decrease in niobium content, increase in carbon content, and other minor adjustments have combined to give less oxidation and less crack propagation.