After a strike period, a petrochemical plant is in the final phase of restart when an employee smells a strong odour of oil while patrolling a steam cracking workshop. He raises the alarm and is soon joined by other employees. They eventually find a poll of gasoline on the ground. By inspecting the pipe rack above the pool, they discover a leak in a pipe (DN = 100, 4 “) carrying gasoline into storage tanks. Thanks to fumaroles, another leak is also detected on a neighbouring pipe (DN = 200, 8 “) carrying liquid propylene (P = 15 bar, T = 35 ° C) to a heat exchanger of the cooling circuit. Closer inspection shows that propylene is slightly leaking at the solder pad of a pipe support. As a leak on a propylene pipeline is a major accident scenario and given the impossibility of installing a sealing collar, the operator resolves to stop immediately the steam cracker. Gas detectors are set around the leak and a damp cloth is used to absorb the leaking product.

The investigation led by the operator identifies the common cause of these leaks: external corrosion of the pipe at the line supports. Five years ago, half-shells were installed as a way of limiting the phenomenon of external corrosion of piping in contact with the metal frame of the support. Since the pipes were in operation, the welding of the shells have not been performed and an adhesive product (glue) was used instead. Despite a fresh coat of paint on the pipes, their profile has remained uneven and the glue was unable to provide an adequate seal to prevent water seepage over time. These infiltrations accelerated the corrosion of the piping sections in contact with the supports, creating small leaks not visible during the setting in pressure of the piping. Corroded sections are cut and replaced by new ones, whose half-shells have been previously welded off site. A general inspection of pipe supports is launched and the half-shell installation procedure is reviewed. The steam cracking workshop restarts 5 days later.