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.
Previous Part 3 captured the Plastic Liner Technology.
5.0 Future Prospects
Plastic will enable a number of novel approaches to subsea pipelines. Some are discussed below.
In this application, a number of commercially marginal accumulations are aggregated. This has the benefit of allowing shared costs and downside mitigation because if one field proves uneconomic during development drilling, the infrastructure procured for it can be re-directed to the next field on the list.
Such sophisticated procedures are not necessary however, simply the fact that the pipeline’s condition can be assured means that when a field is decommissioned, the flowlines can be recovered and transported to a new location, possibly without requiring refurbishment at a beach location.
5.2 Flow assurance
Once plastic lining is accepted, the benefits for flow assurance can be explored. Benefits already discussed include non-stick layers, but insulation benefits can also be optimized. An internal insulation is very efficient, and may be more economical that external coatings, particularly in deep-water applications.
The level of contamination in a plastic lined pipeline will be less than a corroded steel pipeline. It will therefore be easier to clean at the end of its life, allowing the various materials to be recycled. This would break the present unsustainable practice of using pipelines as disposable items and sending the recovered materials to landfill. Because the liners are not bonded to the pipeline, their recovery will not be labor intensive, thus overcoming one of the major difficulties of external coatings which are purpose designed to be difficult to remove. Also, as the liners are thermoplastics no chemical reversion processes are involved, simply re-melting and purification. Ideally a similar approach would also be used for the external coatings so that the lined pipe and coating materials can also be reused.
5.4 Flow Modifiers
Because the plastic is easy to be formed, it is possible to cost-effectively “rifle” the inner surface to assist slug formation and thereby improve flow assurance.
5.5 Intelligent pipelines
The potential also exists to insert communications links in the protected space between the plastic and the steel. For example a fiber optic element could be used to communicate with the wellhead or obtain operational parameters such as temperature and pressure from the pipeline itself.
5.6 Subsea Refurbishment
Plastic lining also offers the possibility of refurbishing old and corroded pipelines. The technology for this is widely used onshore and it could be converted for use subsea.