Field Joint Protection

After the joints of plant–coated line pipe are welded at the right–of–way, they need to be protected. It is vital
to make sure that the coating used for the girth weld is compatible with the main coating of the pipe, without detriment to the weld coating.

The products used for protecting girth welds of plant coated pipe are:

  • Heat–shrink sleeves;
  • Liquid coatings — these range from coal tar polyurethane to urethane and epoxy;
  • Cold PVC or PE Tape — generally these are over the ditch grade cold tapes which are cut and manually wrapped over a joint after it has been heated and primed.

The predominant coatings for girth welds are heat shrink sleeves, powdered FBE and some liquid coatings. However for mainline coatings of 3–layer PE or PP only heat shrink sleeves should be used for reasons of compatibility and long term
in–service performance.

The use of two–component coatings for protecting the girth weld may be a good solution in some cases, where two–component material or coating is used
on the main pipe; however it requires very thorough surface preparation, the use of relatively expensive equipment — special spray equipment is required for these often plural component products which require expert handling in field conditions to assure uniform results — and is labour intensive.

Another factor, limiting the use of this type of coating is the poor compatibility with polyethylene and polypropylene based coatings and limitations in long–term properties in terms of soil stress, water penetration resistance and durability
of the functional adhesion at the interface.

 

 

application of heat shrink sleeve
as field joint protection