Plastic Lined Pipelines for Corrosion Control [PE lining]

Due to space limitations on offshore platforms the treatment of well head fluids is expensive. To reduce the costs there is a move towards unmanned offshore platforms, or subsea completions. The result of such moves is that the pipelines are required to carry all produced fluids, including wet acid gases, in the unprocessed condition to a shore terminal for treatment.

When the predicted internal corrosion rate of the pipeline exceeds an acceptable value for unprotected C-Mn steel, additional measures must be taken. Corrosion inhibitors can be injected and will give reduced corrosion in most environments, but they require additional offshore facilities and can be difficult to optimise throughout the length of the pipeline. As corrosivity of the produced fluids increases, pipelines can be specified in corrosion resistant alloys (CRAs) such as duplex stainless steel, but the high cost of these steels may make the development of the fields uneconomical. An alternative to in-pipe treatment and CRAs is to use an internal coating, or lining, between the product and C-Mn steel pipe. Coatings are usually liquid applied organic materials, bonded to the internal steel surface. The long term performance of these materials can be variable and require excellent surface preparation at the application stage. Loss of adhesion, caused by poor preparation, or lack of cover on some areas can significantly reduce the service lifetime of the coating.

The chemical industry has, for many years, used non-bonded linings (eg thermoplastics, elastomers, glass etc) for corrosion control. Traditionally these have been applied to short, flanged pipe lengths and connected using insulated bolts. The lining of buried 'low pressure' gas and water distribution mains, with polyethylene (PE), is a well established technology for renovating existing pipes coming to the end of their useful life due to corrosion or joint leakage (Ref 1). These non-bonded lining techniques rely on the strength of the PE pipe to retain the internal gas pressure and can be used to line continuous pipes approximately 500 metres long.
This paper reviews the use of non-bonded thermoplastic linings to control internal corrosion in high pressure carbon steel pipelines carrying aggressive fluids.