Transgranular stress corrosion cracking in oil and gas linepipe was studied by testing full-scale pipes in soil environments. Three pipes made of Grade 359 (X-52) and Grade 414 (X-60) steels were used. Sixteen cracks were prepared on the external surface of each pipe, and crack growth was monitored and studied as a function of the pressure level and pressure fluctuation, the latter being described by the minimum to maximum stress ratio (R) and the loading rate.
The overall results suggest strong mechanical effects on crack growth. Crack growth rates were found to be affected by both the pressure level and the level and rate of pressure fluctuation. For the Grade 414 pipe, reducing pressure fluctuation by increasing R from 0.6 to greater than 0.97 reduced the crack growth rates to below 5*10−9 mm/s, the detection limit of the crack depth measurement system used. Similar effects of pressure fluctuation were also seen for the Grade 359 pipes.