Stress corrosion cracking of stainless steel pipes for Methyl-Methacrylate process plants

In a Methyl Methacrylate (MMA) plant, tree-like transgranular cracks were found near the weld of a pipe that had been used for transferring MMA material at 110 °C and 0.77 kg/cm2. The pipe was made of ASTM A312 TP304 stainless steel. s study, it was shown that the failure was due to the stress corrosion cracking (SCC) caused by the chloride that remained in the pipe. Corrosion pitting occurred on the inside surface of the pipe. The stress corrosion cracking started from the pits and grew out through the thickness. Concentrated chloride was found in the deposit stuck to the pipe in addition to the pre-process MMA materials. Many work-hardened grains were observed in the area of SCC, providing the evidence of high residual stress due to welding, which could serve as the driving force for the SCC. Recommendations are made for preventing further failure due to SCC in such cases.