Not all pipelines are made equal.
Some steel pipelines transport media that is neither abrasive nor corrosive and the internal surface of the steel pipe wall may be left bare, as there is no need for additional protection.
Other steel pipelines, intended to transport aggressive media, are internally lined with a protective material that is often heat sensitive. Depending on the transported media, these liners may be thin film bonded liners (liquid epoxy, fusion bonded epoxy, or polyurethane paint), thick bonded liners (rubber or polyurethane), thick unbonded liners, (high density polyethylene (HDPE), polyacetal (PA11 or PA12)), or other heat-sensitive protective materials.
Welding is universally recognized as the safest, most efficient, and most economical method of building onshore and offshore pipelines from individual pipe sections. However, welding pipes which have been internally lined with thermally sensitive materials is not a straightforward process. The high temperatures from the welding processes will degrade or destroy the internal lining at the weld zone, leading to corrosion that will reduce the lifespan of the entire pipeline.
This paper focuses on welded joint systems that answer this technical and economical challenge.
The desirable characteristics of an ideal welding system for pipe with thermally sensitive linings are discussed, and welding systems already developed for the following welded and lined pipeline combinations are presented:
- Butt welds, butt strap lap welds and bell and spigot lap welds for lined pipes with thin film bonded liners: liquid epoxy and fusion bonded epoxy
- Butt welds for pipe with thick bonded liners: rubber and thermoplastic polyurethane
- Butt welds for pipe with thick unbonded liners: high density polyethylene (HDPE)
In-house qualification tests, third party qualification processes as well actual field applications are also presented and discussed, demonstrating that the welding systems developed are both technically and economically feasible.