Failure of fluorocarbon copolymer pipes subjected to mechanical strain in an alkaline environment

A failure analysis was carried out on leaking fluorocarbon-based copolymer pipes used in a cleaning and disinfection plant. Pipes conveyed a solution of sodium hydroxide and showed leaking after two months of service. Leaks originated from reddish-colored cuts located on the bending curves of the external surface of the pipes. Experimental findings and literature review pointed out that a combined effect of chemical degradation and mechanical strain (similar to stress corrosion cracking) triggered the failure. This type of degradation developed in high pH hydroxide solution due to dehydrofluorination of the exposed surface, starting material embrittlement and formation of crazes and microcracks. An applied mechanical deformation accelerated the crack opening and the solvent diffusion, up to the consequent pipe leaking and failure.