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In common with all downstream oil and gas plants, chemical/petrochemical plants, and production plants, power generating facilities need storage and process tanks whose internals require linings to protect against contamination of the cargoes and corrosion of the structure. This article gives an overview of the key features needed for vinyl ester and epoxy tank linings, particularly at elevated temperatures. The article is not intended to be a comprehensive guide to these two types of linings, nor is it intended to address other generic types of tank linings.
i'!llIealion Prnletlion
The main purpose of most tank linWlgs is to pr<Mde a barrier to corrosion. For corrosion to occur, there must be an anode, a cathode, afld an electrolyte bridge for electron transfer. Because of its heterogeneous nature, steel contains both potential calhodic and anodic sites. To prevent corrosion, a barrier (lining) must De placed to block the electrolyte bridge between these sites and any potential aggressive chemicals in the environment.
Permeation is the passage of molecules, usually water molecules, through the lining. Permeation protection is, therefore, the most critical characteristic 01 a corrosion barrier coating. Once the lining is permeated. water molecules have reached the substrate, and an electrolyte bridge can be established, potentially initiating corrosion. As iron forms iron oxide, the iron eltPands, increasing in volume several magnitudes. This e~pansion forces the lining offthe surface and forms b~sters. The loss of adhesion accelerates additional permeation and further iron oxide formation, which will eventua~ Iy lead to breaks in the lining system.
The permeation rate for afly tank lining should be listed on the producfs technical data sheet (IDS) as pemHnch and measured in accordance with ASTM E-96. Glass flakes or other inert fi~ers whose permeability is lower than the resin binder are c~ manly added to vinyl ester and epoxy m.,g systems to mprove ther performance.
TemperalUre AesislanCe
l inings will have a glass transition temperature fTgl, the point at which the tining starts to shiftfrom solid to ~quid . The maximlKll temperature recommended tor the lining performance win be below its T g' Most TOSs for linings with temperature resistance report a temperature close to the T g as the maximum operating temperature in dry conditions, Immersion temperatures are usually a function of...