Pipe coating system

Various organic coatings are in use for pipeline passive external corrosion protection , which are supplemented with active corrosive protection i.e. cathodic protection. The choice and selection of particular coating system is dependent on the various considerations, such as extermnal stresses the coating has to withstand ,compatibility with cathodicprotection and its current demand , soil characteristics , operating temperature etc.

Essential properties that a particular coating system should posses are as under :

1.Protective coating  must remain defect free with a practical limitations over a period of time , specifically for areas where temperature fluctuations are wide .

2.coating must be tolerant  to handling during construction &field bending and in service deterioration.

3.Following are the essential properties of coating system:

--Impact  Resistance

--Penetration Resistance

--Resistance to cathodic disbondment

--Stability at elevated temperature

--Rusistance to soil stress

--Reistance to water absorption

--Chemical resistance (Acids &alkali)

--Volume resistivty

--Flexibility to bending

--Hardness (abrasion resistance )

--Maintenance and refurbishment frequency

--HSE consideration

--Resistance to damages during handing

Three Layer Poly Ethylene/ Propylene(3LPE/3LPP)coating3LPE/3LPP coating system is a multilayer coating composed of three functional components: a high performance fusion bonded epoxy(FBE),followed by a copolymer adhesive and an outer layer of Medium Density Polyethylene (MDPE) or High Density PolyethyleneHDPE), which provides protection against external corrosion.
The codes and standards for 3LPE are ISO 21809-1,DIN 30670 or CAN/CSA Z245.21.
Fusion Bonded Epoxy (FBE):First layer of FBE shall be 150 microns thick.
Adhesive:Second layer of extruded co-polymer adhesive, 200 microns thick.Polyethylene (MDPE/HDPE): Third layer of extruded polyethylene (MDPE/HDPE) or polypropylene (MDPP/HDPP), 1.6- 2.95 mm
thick.Application of Coating:Surface preparation of pipe by blast cleaning,subsequent to pipe heating fusion epoxy powder shall beapplied and after that extruded adhesive shall be applied over the pipe. Finally extruded polyethylene (MDPE or HDPE) layer shall beapplied over the adhesive layer.
Total coating thickness is generally < 3.0 mm for pipe dia < 24" and 3.3 mm for pipe dia 32" & above)