A chemical project transports a chloride-containing medium (about 800 ppm, 65°C). The original design used 316L, and pitting perforation occurred after two years of operation.

Root cause: the combined effect of temperature and chloride ions placed 316L in the critical zone, and the welds were not sufficiently passivated.

Remediation: key pipe sections and weld areas were changed to 2205 duplex steel, while the rest was retained as 316L with enhanced pickling and passivation; cost increased by about 20%, but the expected service life is increased by more than 3 times.

Experience: material selection in the chemical industry must be based on medium analysis reports, not merely on grade conventions; welds and crevices are the starting points of corrosion, and structure and process are equally important.