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Pipe Coating, Lining and Cladding

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.

COATED PIPES

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)

Coated pipes

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
  • Application of flame in pipeline environments has traditionally been the cause of workplace fires and explosions
  • Requires application of flame to create adhesion
  • Limited heat resistance.
  • Maximum 225°F to 250°F.
  • Limited dimensional stability
  • Features just a borderline hardness
  • Shows poor resistance to sulfur, amines, oxygen, and other oxidants.
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
  • Rather expensive application cost per meter
  • FBE materials are expensive
  • The pipe and the coating materials must be heated to approx 250°F
  • Long lead times
Asphalt enameled and polyurethane (PUR) Cheap and superior to coal enamelReduces the hysteresis
Fast treatment
  • Modest resistance to chemical aggression
  • Strict temperature ranges
  • Limited dimensional stability

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.

3LPE pipe coating

(Source: Wasco Energy Youtube Channel)

LINED PIPES

Lined pipes

Lined pipes are fitted with an internal protective material which is mechanically inserted into the tubular section. The lining material is fitted into the pipe at the end of the manufacturing process. It is clear that internal lining materials, which have an own thickness, reduce the bore size of the pipe.

The most pipe lining materials are:

  • Teflon (PTFE)
  • Cement mortar
  • Liquid epoxy
  • Glass
  • Fusion bonded epoxy (FBE)
  • Polyethylene
  • Bituminous asphalt
  • Zinc

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).

Clad pipes are also called CRA (which stands for “corrosion resistant alloy”).
 The cladding process consists of the application, in the inner part of the pipe, of a layer of higher grade material onto a lower-grade base material of the pipe.
Clad pipes are used for fluids that would quickly corrode carbon-manganese steels. The bonding between the two materials is metallurgical and can be achieved by welding the two together or with explosion techniques (whereas lined pipes feature a mechanical bonding of different materials).
Pipe cladding is used to enhance the durability and the resistance to corrosion of a pipe while keeping its final costs at acceptable levels. Of course, clad pipes are more expensive than lined pipes, as the overlay materials used are, generally, noble metals.
Clad pipe

Comments

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  • Informative post on Non-metallic coating, After a read I got a clear picture on types of non-metallic coating and able to understand the various pipes used to avoid corrosion. Thank you for sharing the post.

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