Field Joint Coating
The root cause of premature breakdown of coatings at the field joint area usually stems from a lack of detail within the Field Coating Specifications in terms of technical requirements when compared to the rigorous attention given to factory-applied coatings. Evidence would suggest that unless practical attention is given to the variances induced by local environmental factors, which require systematic planning to negate, then poor workmanship/inspection could result. To ensure the entire pipeline coating system withstands the ingress of corrosion throughout its design life the importance of the field joint coating system is paramount.
Factory-applied coatings to pipelines are carefully specified with known variances in surface preparation and application controlled and keenly monitored by any number of inspection bodies who have a stakeholding in the finished project. The lifetime design protection is assured through pre-qualification and process qualification activities to ensure the coating plant can repeat 100% compliance in a production environment. In essence the field joint coatings should match the performance and design criteria of the factory-applied coating to provide one homogeneous layer protection system along the length of the entire pipeline.
ISO 21809-3 provides a prescribed method to confront the vagrancies of field joint coatings. So, for each coating classification there is attention to pre-qualification and process qualification to mirror the rigour given to factory-applied coatings. Pipeline Protection can provide materials compliant to ISO21809-3 and also field joint services compliant to the same standard.
According to ISO 21809-3 Field Joint Coatings can be classified in groups and designated codes as demonstrated in the following table;
|Code||Type of Field Joint Coating|
|1A||Hot Applied Bitumen Tape|
|1D||Cold Applied Polymeric Tapes|
|2A||Heat Shrinkable materials – PE Based|
|2B||Heat Shrinkable materials – PE based, applied over primer|
|2C||Heat Shrinkable materials – PP based, applied over primer|
|3A||Single Layer Fusion Bonded Epoxy powder|
|3B||Dual Layer Fusion Bonded Epoxy powder|
|5A||Flame-sprayed polypropylene powder over epoxy layer|
|5B||Polypropylene tapes/sheets hot applied over epoxy layer|
|5C||Injection Moulded polypropylene over an epoxy layer|
|5D||Flame sprayed polyethylene powder applied over an epoxy layer|
|5E||Polyethylene tapes/sheets hot applied over an epoxy layer|
|6||Thermally Sprayed Aluminium (TSA)|
|7||Hot-applied microcrystalline wax coatings|
|8A||Elastomeric coatings, Polychloroprene|
|8B||Elastomeric coatings, EPDM|