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, moisture.
- Prevents direct contact of 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 have 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 are increasing day be 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 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, anti-corrosive coating can be categorized into the following types
- Natural Paints
- Synthetic Resins
- Fiber Reinforced Plastics
- Glass lining
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.
Specific application dictates the type of anti-corrosion coating to be used.
Rubber Lining as Anti-corrosive agent
Types of Rubber Lining:
- Natural Rubber
- Butyl (isobutylene)
- Halogenated Butyl – e.g. Chlorobutyl
Applications of Rubber Lining:
- Resistant to acid, abrasion, oil, seawater.
- High temperature and corrosive service, where natural rubber fails.
- Used for High-Temperature Corrosive service e.g. Reaction vessels
- For Hot and abrasive services
- 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
- 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 TETRAFLUORO ETHYLENE
- ECTFE – ETHYLENE CHLOROTRIFLUORO ETHYLENE
- PVDF – POLYVINYLIDENE FLUORIDE
- PP – POLYPROPYLENE
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
- -temperature shock
Application of High-Build Coatings
Typical applications of anti-corrosion high-build coatings are
- Mixed beds
- Water storage tanks
- Chemical storage tanks
- Chemical day tanks
- Filter housings
- Wet bench components
- Vacuum de-gasifiers
- 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
- Vessel configuration – dimensions, complexity
- Desired fluoropolymer
- Thickness of lining
- 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 < 10 mpy (mills per year)-USE THIN LININGS
- THICK LININGS – >25MILS OR 0.635MM
- THIN LININGS – < 25MILS OR 0.635MM
Coatings-Linings thickness selection criterion
Use Thin Lining For
- Product purity
- 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