| Popis: |
Publisher Summary Stress corrosion cracking (SCC) occurs on the soil-side of a buried pipeline when the coating breaks down and groundwater comes in contact with the steel. This chapter examines the growth of single cracks, and proposes a superposition model incorporating the environmental, and mechanical effects to describe the later stages of near-neutral SCC growth using laboratory testing that duplicates pipeline conditions. Cantilever bending loading is used for the SCC tests on both the edge and surface crack specimens. Crack tip loading is characterized using the linear elastic stress intensity factor; K. SCC tests are performed under anaerobic conditions to simulate the conditions of a buried pipeline by enclosing the specimen and electrolyte chamber in a larger outer environmental chamber. This, in turn, is sealed and continuously flushed with pure N2 gas. Microscopic examination of the edge crack specimens reveals that the cracks are transgranular, traversing both pearlite, and ferrite grains. For the short-term tests of less than 80 days, the cracks remain narrow and sharp. This is in contrast with the long-term test results, where the cracks are blunt and wide. As the exposure time in NS4 solution increases, all the cracks experience general corrosion causing widening, despite the anaerobic environment. |
