| V. PIPELINE COATING
A. INTRODUCTION
- Coatings are applied to provide a corrosion barrier and an abrasion
barrier. Directional crossings generally encounter varying materials
and often can be exposed to extra abrasion during the pullback. An outer
abrasion resistant overcoat is often warranted. To facilitate the pullback
of the pipeline the coating should bond well to the pipe to resist soil
stresses and have a smooth, hard surface to reduce friction and maintain
the corrosion barrier. As in any pipeline construction, the recommended
external coating system should be compatible with any specifications
for the field joint coating or any internal coating.
B. PIPE COATING - The recommended pipe coating is mill applied
fusion bonded epoxy (FBE). The recommended minimum thickness is 20 mils.
C. JOINT COATING - The coating application of the weld area is
the most critical field operation to maintain a smooth abrasion-resistant
pipe string. It is recommended that the girth weld be coated with FBE
powder utilizing the induction heating coil and powder application machine
to a minimum dry film thickness of 25 mils. As an alternate, two component
catalyzed liquid epoxy may be applied to the girth weld area to a minimum
dry film thickness of 25 mils using a paint brush or roller. Tape should
never be used for joint coating on the pullback portion of a directional
crossing.
D. COATING REPAIR - It is recommended that small coating damaged
areas be repaired with a polymeric melt stick patching material. Holidays
larger than 1 in. in diameter should be repaired utilizing the two component
catalyzed liquid epoxy applied with a paint brush or roller. Tapes should
never be used for repair of coating damaged areas on the pullback portion
of a directional crossing.
E. ABRASION RESISTANT OVERCOAT - As an extra abrasion resistant
barrier for crossings that may encounter stones, boulders or solid rock
it is recommended the FBE coated pipeline be over coated with an epoxy-based
polymer concrete. The material should be applied at a mill or with a
portable yard coating machine to a minimum thickness of 40 mils. Girth
weld and coating damaged areas should be field coated using an epoxy-based
polymer concrete compatible with the overcoat material. The patch material
should be applied so the material tapers uniformly and feathers into
the original coating. Stability of the pipeline in drilled crossings
is not normally a concern so a Portland cement type concrete coating
is not recommended.
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