What is the difference between external pipe coating and internal pipe-lining and cladding? External pipe coatings are used to protect the metal from corrosive environments (3LPE coated pipes are the most common choice). Internal lining (example PTFE) protects the pipe from corrosive fluids. Clad pipes (CRA) have the inner surface covered by higher grade materials to achieve stronger resistance while decreasing the overall pipe cost.
Pipes may be coated externally to be protected from corrosion, erosion and possible mechanical stress.
Pipe coating consists of the application of metallic, or non-metallic, materials on the external surface of the pipe (either seamless or welded).
The most common materials to coat pipes externally are:
- Non-metallic pipe coating: Paints, varnishes, lacquers, bituminous coatings, resins, plasticizers, Greases, waxes, oils, Plastics (polyurethane, polyethylene, Rilsan, PTFE, PVC), Elastomers (various types), Vitreous enamel, Cement mortar
- Organometallic pipe coating: Paints pigmented with metals in powder form (aluminum, zinc, lead, stainless steel), Paints containing zinc ethyl-silicate
- Chemical modification: Phosphating, Chromatin, phosphating, Black finishing, and browning
- Cementation (physiochemical modification)
The main types of non metallic pipe coating materials, and their advantages/disadvantages, are summarized in the table below:
|Pipe Coating Type||Advantages||Disadvantages|
|Three-layer Polyethylene (3LPE) and 3 layers Polypropylene (3LPP)||Low material and application cost||
|Polypropylene (PUR)||Recommended for deep sea applications with relatively high temperature and pressures||Polypropylene is liable to chain degradation from exposure to heat and UV radiation such as that present in sunlight.|
|Fusion Bonded Epoxy (FBE)||Excellent chemical resistance and great dimensional stability with minimized hysteresis||
|Asphalt enameled and polyurethane (PUR)||Cheap and superior to coal enamelReduces the hysteresis
3LPE COATED PIPES
3LPE coated pipes feature a three-layer polyethylene coating consisting of:
- a high-performance fusion bonded epoxy (FBE),
- a copolymer adhesive
- an outer layer of polyethylene which provides tough, durable protection against corrosion and erosion.
3LPE pipe suit medium to high operating temperatures.
(Source: Wasco Energy Youtube Channel)
The most pipe lining materials are:
- Teflon (PTFE)
- Cement mortar
- Liquid epoxy
- Fusion bonded epoxy (FBE)
- Bituminous asphalt
CLAD PIPES (CRA)
A clad pipe combines the strength and toughness of a carbon steel pipe with the corrosion resistance of a stainless or duplex pipe (or even higher grades, as nickel high-alloyed materials like Inconel, Incoloy, etc).