Plastic lining has been applied as a means of providing cost effective corrosion protection to pipelines, and it is widely used for water injection pipelines both onshore and offshore.
Plastic lining has been applied as a means of providing cost effective corrosion protection to pipelines, and it is widely used for water injection pipelines both onshore and offshore. The technology was originally developed as a means of refurbishing old pipelines and there are now many thousand miles of pipelines refurbished in this way. It is therefore a well-proven technology in a wide variety of services including water, gas, petroleum and many other sectors.
However, it has only been applied to a very limited extent in unprocessed hydrocarbon production pipelines, mainly in locations famous for the corrosivity of the produced fluids.
2.0 Benefits of Plastic Lining
There are a number of ways in which plastic liners can offer benefits to hydrocarbon production pipelines. These are:
- Thermal benefits from the plastic’s insulating properties
- Low surface energy coatings giving flow assurance benefits
- Corrosion prevention
2.1 Thermal Benefits
Plastics have low thermal conductivities compared with metals. They are therefore insulators, and it is a fact that insulators are most efficient when they are located close to the warm source. A plastic lining therefore offers better insulation than the same material used externally to the pipeline.
The benefit of this insulation can be taken in a number of ways including reduced external insulating layers (which are very expensive, particularly in deep water pipelines), and lower preheat on reception at a processing facility. In addition, as the steel of the pipeline is cooler, the axial forces that drive buckling are less. In the case of upheaval buckling, less backfill or rock dump may be required, and in the case where lateral buckling is an issue, special features such as snake-lay, expansion spools, etc can be avoided.
2.2 Low Surface Energy Coatings
It is possible to co-extrude a base plastic with a layer of different material. The base layer is selected for its low cost and toughness, and the other layer is selected for some other desirable property. This co-extrusion process is routinely used for petrol pipelines, where permeation resistance is obtained from an internal layer of Nylon that is extruded over a cheap yet tough Polyethylene base.
Another example is fiber optic cable ducts, where a low-friction layer reduces cable installation loads.
In a similar way, where flow assurance benefits are desired, a silicone or Teflon enrichment could be provided as an inner layer, providing non-stick properties. In this way it is possible to minimize the adhesion of hydrate crystals, waxes, etc., and thereby provide flow assurance benefits.
2.3 Corrosion Benefits
The main focus of this discussion is on corrosion benefits, because costs have been unnecessarily high on some projects where expensive corrosion resistant metals have been used.
Plastics can offer enhanced performance at lower cost and proof of this can be found from their widespread use in the engine compartment of motor vehicles and in flexible pipelines.
See Part 2 for Plastic Lining Geographical, Economic, Social Factors.