Lining – What Is Piping: All about Piping Engineering

The purpose of this article is to provide brief information about different types of pipe internal coatings/linings, their uses, advantages, and limitations. Purpose of Internal Coating Pipe internal corrosion preventionFlow improvementTo minimize deposit formation Types of Pipe Internal Coatings / Lining Fusion Bonded Epoxy (FBE) CoatingGlassflake Coatings (Chemflake, Belzona, etc)PE (Polyethylene) Lining / ROTO Lining Pipe External Coatings Stopaq, FBE, 3LPE, 3LPP FBE (Fusion Bonded Epoxy) Coating Fig. 1: Image showing FBE Coating FBE a high-performance anti-corrosion powder coating for moderate operating temperatures, generally suitable up to 80 °C. For higher temperature application special FBE grades such as TK-216 (up to 95 °C) & TK-236 (up to 120 °C) can be qualified subject to Client’s approval. FBE Coating Application Procedure Visual inspection before blast cleaning to check the presence of oil, grease, etc. The steel surface is thoroughly cleaned by blast cleaning which removes rust, scale, etc and produces a rough surface finish. The roughness value required is 50 – 100 micron. Heating: Induction heating or oven heating, usually in the range of 180 to 250 °C The application and curing stage Internal surfaces of pipes are coated using a spray gun, which travels from one end to the other end of the heated pipe at a uniform speed, while the pipe is being rotated in its longitudinal axis. After coming in contact with the hot surface, the powder melts and transforms into a liquid form. This liquid FBE film flows onto the steel surface and soon becomes a solid coating by chemical cross-linking, assisted by heat. This process is known as “Fusion Bonding”. Standard FBE coating thickness ranges between 250 to 500 microns (0.25 to 0.5mm). After field welding of the pipe ends, FBE can be applied to the weld area as well. FBE Coating Advantages Suitable for higher temp. compared to PE/ROTO liningExcellent adhesion to steel provides superior long-term corrosion resistanceIt can be applied to various pipe diameters from 2” to over 48”.It can be applied to a wide range of thicknesses.Good chemical resistance under most soil conditions.Good abrasion and high impact resistance Limitations of FBE Coating The maximum life of the FBE coated pipe is 12 years, and if the plant design life is 25 years, one piping replacement is required.Can be applied only in the shopApplicators not readily availableComplex design Internal Glass Flake Coating (Chemflake, Belzona etc) Fig. 2: Image showing internal glass flake coating Chemflake/Belzona coatings are glass flake epoxy coatings as per PCS - 8 of SP-1246, normally suitable up to 93 °C operating temperature (Belzona can be used up to 120 °C by using specific Belzona grades). Suitable for higher pipe sizes & where Roto lining can not be carried out because of the weight limitation of pipe spool. Generally carried out inside a flanged pipe spool, for joining non-flanged pipe spools Thru-kote sleeves are used. All flanges of Chemflake & Belzona coated piping shall be provided with a weld overlay of suitable material prior to dispatch for internal coating. Internal Glass Flake Coating Application stages Cleaning – blast cleaning. The roughness value required is 75 - 130 micron.Spray - Normal airless spray or two-comp. airless spray equipment.Brush - Recommended for stripe coating and small areas. Care must be taken to achieve the specified dry film thickness.Curing – 1 coat requires around 24 hr to get a total dry film. DFT : 2 x 750 micron (for Chemflake) 1 coat of 1000 micron (for Belzona) Advantages of Glassflake Coating Good chemical resistance,Good solvent resistance,Good adhesion,Low permeability,Good weather properties,Excellent gloss retention. Limitations of Glassflake Coatings Temperatures & pressure-dependent – suitable only up to 10 bar pressure & for non-flowing or less velocity fluids.Not suitable for abrasive fluids/slurriesMay cause skin irritation,Requires recoating intervalsChalking (for epoxy)-Time ConsumingVery costlyUsed only for less no. of spools, not for the entire project scopeDesign life is questionable by PDO, maybe up to only 3 - 4 years PE & ROTO Lining Fig. 3: Image showing example of PE & Roto Lining For further design details about PE/Roto lined piping please click here