Corrosion-Fatigue (Circumferential) Cracking in Cr-Mo Low Alloy Boiler Tube Steels: Part 2—Laboratory Simulation

Abstract

A laboratory procedure which causes cracking similar to that found in the waterwalls of coal fired boilers was developed. The procedure was designed to simulate the mechanism of crack initiation by a combination of intergranular corrosion and thermal stress cycling. It can also be used to study the subsequent environmentally assisted fatigue crack propagation. A finite element analysis of the transient thermal stresses induced by the laboratory simulation procedure was also performed in order to understand and document the nature and magnitude of the thermal stresses in the specimen. The result is that, although the magnitude of the thermal stress cycle in the simulation was greater than that calculated for in-service tubes, its nature is the same. This simulation procedure has potential as a tool to evaluate the relative resistance of materials to circumferential cracking and as a life estimation procedure for new boiler tube surface modifications.