The degradation of plastics & rubbers used in corrosion protection systems

Abstract

Thermoplastics, thermoset resins, rubbers and chemicals which are used for corrosion protection may themselves be the subject of degradation through mechanisms that are not related to solar radiation. Coatings, liners, umbilicals, O-rings, seals or other protective systems can all be attacked in a slow but insidious way. This gradually leads to degradation, leaks and loss of physical and/or mechanical properties, often promoting serious corrosion of the metal substrate and requiring costly repairs.Hydrolysis of the polymer is one of the most common breakdown mechanisms, which applies to polymers such as nylon, polyurethanes, and polyesters that have hydrolysable linkages in the main chain. Other mechanisms include oxidative degradation, particularly if air can gain access, and biodegradation of the polymer. Accelerated aging tests followed by mechanical testing and molecular weight analysis are the most useful general methods for appraisal of the likely future state of the polymeric material.The following examples of polymer compromised corrosion susceptible environments will be discussed:*An assessment of the suitability of elastomeric shims or wedges to replace metals*Biodegradation of sulphur and consequential corrosion of steel supports and rail carts*Cold flow of Teflon PTFE and other fluoroplastics*Glycol heat transfer and hydraulic fluid systems*Pipe Coatings*Polycaprolactone and polyester polyurethane failures*Nitrile and Kalrez extrusion*Viton explosive decompression*Water and rubber do mix and can degrade Viton elastomers*Ageing of Rilsan sheath in pipes*Epoxy failures due to thinners, salts and exceeding the pot life Amine blush*"(WSMs)", such as phthalic acid and propylene glycol derived from the polyester resin, present in exudates derived from the FRP laminate.