Internal Pressure Creep Properties of Electric Resistance Weld Tube for Boiler

Abstract

Creep rupture tests on tubular specimens under internal pressure at high temperatures give the most reliable information for tube design of boilers, because the tubes for boilers are subjected to multiaxial stresses in actual use but the maximum principal stress is tensile hoop stress.
In this study, the creep rupture tests on the tubular specimens of carbon steel under internal pressure at high temperatures were carried out. Furthermore, the burst tests on the thickness-deviated tubular specimens were done in order to investigate the fracture behavior under internal pressure. The results obtained are summarized as follows:
(1) The creep rupture properties of the carbon steel tubes produced by the electric resistance welding process, JIS-STB 42 EG and BS-ST 45 ERW, were proven not at all inferior to those of the seamless tubes.
(2) In the internal creep rupture tests, all specimens ruptured at the base, not at the welded portion, and the slight deviation in wall thickess of a steel tube affected the location of initial rupture.
(3) The thickness-deviated tube ruptured at the position of minimum thickness and showed a kind of the notch-strengthening.
(4) The electric resistance weld tubes were recognized to have sufficient mechanical properties for use as boiler tubes from the results of material strength tests, microscopic observations and creep rupture tests under internal pressure on the tubes used for 7954 hours at a 250 MW boiler plant.