Some 2.25%Cr-1%Mo furnace tubes had been removed from service during a modification of the furnace layout after prolonged service (more than the design life of 100,000hr).
Calculation suggested that the tubes were approaching the end of their available lives, based upon the standard creep rupture data available. These tubes were made available to TWI for Remaining Life
Assessment (RLA) by post-exposure creep testing. The wall thickness of the tubes was insufficient for the fabrication of conventional creep specimens and rods of test material were electron beam welded on to sections of matching composition for the larger diameter threaded ends to the specimens. A small-scale programme of accelerated stress rupture tests was performed and it was found that under the design conditions of temperature and stress there was still a very significant creep life remaining and retubing could be postponed for several years.