Caustic corrosion cracking of the octene tube in the fertilizer industry

A carbon steel octene tube has leaked from the fusion zone and caused economic losses. The failure process and mechanism were investigated in this work, by means of scanning electron microscope, electron backscattered diffraction, energy-dispersive X-ray spectroscopy and Scanning Kelvin probe force microscopy. Results showed the failure was attributed to caustic corrosion cracking. The cracking mechanism is anodic dissolution mechanism, including film rupture, intergranular corrosion and repassivation processes. A less corrosion-resistant chemical composition, a larger residual stress after welding and a higher content of hydroxyl ions synthetically resulted in the cracking synthetically. Hydroxyl ions firstly reacted with passive film and caused initiation of intergranular cracks. Residual stress and intergranular corrosion result in an intergranular propagation of SCC cracks.