Mechanical – Page 60 – What Is Piping

Anti Corrosive Coatings on Steel are widely used to protect the pipes from corrosion. The protective coating layer helps the steel material to prevent corrosion and increase the useful life of the material. Anti-corrosion coatings are one of the most effective and economical options for tackling corrosion. Corrosion-resistant anti-corrosive coatings serve the following purposes: Protect metal surfaces from degradation due to oxidation, and moisture. Prevents direct contact with environmental chemical hazards. Acts as a barrier from corrosive materials. prolong the structural life along with increasing their efficiency. Provides chemical protection, abrasion resistance, etc. For industries like oil and gas, chemical, petrochemical, infrastructure, marine, power generation, etc., the use of anti-corrosive coatings and linings has become a necessity to safeguard the huge investments in terms of money, property, and safety of workers. The demand for high-performance anti-corrosion coatings is increasing day by day. A wide variety of anti-corrosive coatings are available in the market to suit the performance requirements of a specific application. Therefore, the selection of anti-corrosion coatings is not an easy process. Various parameters need to be ensured during anti-corrosive coating selection. Sometimes, the coating manufacturer needs to be consulted for some specific information. Corrosion in the Oil and Gas Industry Corrosion in the Piping and Pipeline Industry is quite common. Corrosion is a loss of material due to “REACTION” with the environment. Physical: erosion Chemical: irreversible loss Electro-chemical: electric microcell Biological: bio-fouling Forms of Corrosion Corrosion manifests in different forms as listed below: Erosion: commonly observed in lead-lined vessels; area of the vessel near the impeller Pitting: micro holes in the relatively unattacked surface Selective leaching: dezincification of Cu-Zn alloy Intergranular: welding or improper heat treatment Stress corrosion: welding, cold work, etc. Crevice corrosion: electrochemical cell in the crevice Points to remember The steel surface for coating must be as clean as possible. The metal surface must not have scratches. The anti-corrosive coating itself must be environmentally friendly. Types of Anti-Corrosive Coatings Depending on the materials used, an anti-corrosive coating can be categorized into the following types Natural Paints Epoxy Polyurethane Synthetic Resins Plastics Phenolic Composites Alkyd Lining: Fiber Reinforced Plastics Glass lining Graphite Rubber Again, depending on the anti-corrosive coating application they can be divided into two groups: Anti-corrosive coatings for new pipes, and Anti-corrosion coatings for maintenance and repair work. The specific application dictates the type of anti-corrosion coating to be used. Rubber Lining as an Anti-corrosive agent Fig. 1: Typical Anti-Corrosive Lined Pipes Types of Rubber Lining: Natural Rubber SBR Neoprene(Polychloroprene) Butyl (isobutylene) Halogenated Butyl – e.g. Chlorobutyl Bromobutyl Applications of Rubber Lining: Neoprene Resistant to acid, abrasion, oil, and seawater. High temperature and corrosive service, where natural rubber fails. Butyl Rubber Used for High-Temperature Corrosive service e.g. Reaction vessels For Hot and abrasive services Applications Chlor-Alkali Plant Phosphoric Acid Plant DI water plants Fluoropolymer Coatings & Linings Anti-corrosive fluoropolymer coatings offer a blend of high-performance resins and fluoropolymer lubricants. Consisting of a dry film lubricant, fluoropolymer coating generates a smooth, hard, and slick final coating to provide excellent corrosion and chemical resistance. Advantages of Fluoropolymer anti-corrosion Coatings & Linings Anti-corrosion fluoropolymer coatings also provide the following advantages: resistance to galling non-wetting surface reduced friction non-stick surface electrical resistance and abrasion resistance. Chemical inertness against nearly all substances Broad application temperature range (-30oC to 260oC) Very smooth material surface and anti-sticking behavior Possibility of being electrically conductive Impact-resistant Absorbs pressure variations or impacts Vibration decreasing Insensitive to UV light No softening agents used Weather-resistant and approved for food and drugs service Because of so many benefits, the application of fluoropolymer coating is extensive. Typical examples of anti-corrosive fluoropolymer coating and lining are PFA - PERFLUROALKOXY FEP - FLUORINATED ETHYLENE PROPYLENE ETFE - ETHYLENE TETRAFLUOROETHYLENE ECTFE - ETHYLENE CHLOROTRIFLUORO ETHYLENE PVDF - POLYVINYLIDENE FLUORIDE PP – POLYPROPYLENE Fig. 2: Properties of Fluoropolymers Advantages of High-Build Coatings Drastically reduces permeation through the coating and possible corrosion of the metal substrate. It lowers the metal content of the fluid being handled due to the reduction of permeation, substrate corrosion, and back migration of corrosion products. Extends the life of the coating when exposed to abrasive media Thick coatings can be repaired by welding if mechanically damaged. Thin coatings (<20mil) must be stripped and recoated if repairs are not possible. Thick coatings operate better under pressure-vacuum cycling than thin coatings. The cost of a thick coating is not directly proportional to its thickness. Longer online performance is achieved at only a small additional cost with high-build coatings. Less maintenance is an important benefit. No welds exist with a high-build coated vessel in comparison to one that is sheet-lined. Welds in sheet-lined vessels are a known point of failure. Used in all chemical processes with hazardous, corrosive, abrasive and-or toxic media. Well-established in the chemical, pharmaceutical, and petrochemical industry Ideal in any plant because of their good chemical and physical resistance and long lifetime in service. Absence of sensibility against: -mechanical impact -alternating pressure -vibration -temperature shock -aging Application of High-Build Coatings Typical applications of anti-corrosion high-build coatings are Mixed beds Water storage tanks Pumps Piping Chemical storage tanks Valves Chemical day tanks Filter housings Wet bench components Vacuum de-gasifiers Agitators CMP components Anti Corrosive Coating Selection Criteria The parameters that must be considered while selecting a suitable anti-corrosive coating are Chemical exposure Permeability of the coatings to the materials to be processed Pressure if handling gaseous materials Purity, FDA, and USDA requirements Maximum operating temperature Abrasives, if present Cost Vessel configuration – dimensions, complexity Desired fluoropolymer Thickness of lining Reparability Track record Anti Corrosive Coatings And Linings thickness selection criterion If the corrosion rate of carbon steel is > 10 mpy (mills per year)-USE THICK LININGS If the corrosion rate of carbon steel is 25MILS OR 0.635MM THIN LININGS - < 25MILS OR 0.635MM Coatings-Linings thickness selection criterion Use Thin Lining For Product purity Nonstick Localized corrosion Use Thick Lining for Corrosion prevention Permeation resistance Difference Between Coating and Lining: Coatings Vs Linings In terms of Thickness: Coatings – 10 to 1500 microns (0.01 to 1.5mm) Linings – 3000 to 5000 microns (3 to 5 mm) The coating can be done from outside and inside but the lining is done only inside the pipe. Lining in a pipe means a pipe inside a pipe, but the pipe coating is not the same. Coatings are better than linings with respect to the following: adhesive forces vacuum application heat transfer thermal shock Few more useful Resources for you… An Article on Forms of Corrosion Corrosion under insulation: A Presentation Corrosion Protection for Offshore Pipelines Corrosion Monitoring Techniques & Surveys: A short Presentation Guide for Coating Selection for External Bolting to Reduce Corrosion Application of Anti-Corrosive Linings in Oil and Gas Industry Anti-Corrosive Composites for Oil and Gas Industry