Pressure-Vessel Steels: Promise and Problem

During the past 25 years, numerous pressure-vessel problems have been solved, but in many instances the solutions have led to other problems. Currently, promising developments in pressure-vessel steels are providing such solutions and such additional problems with respect to fabrication and various failure modes. With respect to fabrication, lamellar tearing is being minimized by special melting and solidification practices. However, continuous casting and electroslag-remelting of slabs are currently limited in plate size that can be produced. With respect to bursting, recent studies indicate that high-yield-strength steels have higher burst-strength indices than lower-strength steels even for vessels with nozzles and with notches up to 25 percent of the wall thickness. Strength and therefore resistance to bursting can be increased without loss in toughness through new control-rolling practices, except that these practices are limited to plates up to 3/4 in. thick. New high-toughness line-pipe steels are now available that should be very attractive for pressure vessels that require very high resistance to shear tearing. These low-sulfur steels may be somewhat impaired by sensitivity to splitting as a result of the control-rolling practice. To date, steels have not been developed with improved resistance to fatigue failure. Fortunately, pressure vessels have rarely failed by fatigue. Similarly, resistance to failure by environmental effects is not basically improved by steel composition. This is usually the result of difficulty in defining the effects of the numerous environments that may be involved. These steel developments promise continued improvement of pressure-vessel performance, but usually are accompanied by problems that present new technological challenges.