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1988
Journal Article
Titel
Fatigue and creep crack growth in methane reformer tubes at temperatures above 700 degrees C
Abstract
In order to clarify the problems of transferability for fracture mechanics data in the high temperature regime (above 700 degrees C), creep crack growth and fatigue crack growth experiments have been performed with several types of specimens. Beside standard specimens (1" CT, 1/2" CT, CCP), in some experiments also methane reformer tubes of 120 mm o.d. and 10 mm w.t. were tested. These tubes were stressed by cyclic tensile load or by static tensile load and superimposed internal pressure. The crack growth was monitored by the DC potential drop technique. Fatigue crack growth to be K sub I-controlled up to the highest testing temperature of 850 degrees C. Creep crack growth can be described by the C-integral. As no eta-factors for the calculation of C integral are specified in the literature for tubes with circumferential cracks, finite element calculations were carried out. As a result of this calculation, eta was found to be approximately 1.35 for the geometry described. The influence of crack length on eta is low. In addition to the experiments with tubes in the as received state, two tubes were tested which had been in service for more than 8000 h at 800 degrees C. This condition did not produce any significant influence on creep and fatigue crack growth. (IWM)