Stress Corrosion Cracking of X-60 Line Pipe Steel in a Carbonate-Bicarbonate Solution

摘要

An experimental system was developed to reproduce stress corrosion cracking (SCC) of API X-60 line pipe steels in highly alkaline (pH =10) carbonate-bicarbonate (1 N sodium carbonate Na_2CO_3 + 1 N sodium bicarbonate NaHCO_3 solutions. Intergranular fracture developed in precracked specimens under very low frequency (40 cycles/day to 400 cycles/day) cyclic loading conditions (minimum to maximum stress ratio R of 0.82) at 75 deg C and -650 mVSCE that simulated actual pipeline conditions. Crack growth rates were determined following fradographic examination, and a maximum average growth rate of 2.7 x 10~7 mm/s was measured. The minimum threshold stress intensity for SCC (KISCC) was 25 MPs m. These findings supported the view that rupture of the passive film is responsible for SCC of pipeline steels under highly alkaline field conditions.