メタノール溶液中における低炭素鋼の応力腐食割れ

抄録

Steel drums made of low carbon hot rolled steel sheet (1.2mm thick) filled with a methanol solution of vinyl resin sustained cracking at the beaded regions of drums after two months storage in the summer season when drums were stacked on their sides. The cracks first initiated at the inside surface of drums and propagated intergranually toward the thickness direction. A constant strain test and constant strain rate test were carried out in methanol solutions of vinyl resin to clarify the causes of drum fracture.
It was found that methanol and its derivatives together with the concentration of tensile stress at beads caused stress corrosion cracking of low carbon steel.
The effect of impurities, formic acid, water, and formaldehyde in methanol on the stress corrosion susceptibility of low carbon steel sheet was investigated by the constant strain rate test. Bent specimens of low carbon steel showed high susceptibility to stress corrosion in methanol containing 0.01-0.02 wt% formic acid and 0.05-0.2 wt% water. In this case, over 1.0wt% water inhibited the stress corrosion whereas 0.05-0.2 wt% water worked as an accelerator; formaldehyde worked as an inhibitor in methanol.
Effects of cathodic or anodic polarization and the test temperature on the time to failure were investigated, and it was confirmed that the cracking was active path corrosion and not hydrogen embrittlement.