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The future for protected pipelines

Denis Melot at TOTAL has been working with IFREMER on lifetime prediction of subsea wet thermal insulation coatings, which are complex. The anti-corrosion layer is FBE, which can be tested with NACE, ISO and NORSOK standard methods.

There are no standards for other aspects such as the bonding of the insulation to the FBE, so TOTAL has its own procedure: GS COR 226, before and after ageing. The thermal insulation reacts with the anti-corrosion paint and the field joints. Ageing is tested at the maximum rated temperature, 15C and 30C below that and at 4C. One of the major causes of failure of insulation is poor application and quality control. Trelleborg Offshore offers thermal insulation of pipes.

Polypropylene is increasingly being specified in offshore pipe coatings. PETRONAS Research in Kuala Lumpur, Malaysia has been developing a new 3-layer PP coating system to cut costs and the challenge is to improve the toughness of the polymer. Wasco Coating provided facilities for the coating trials and PETRONAS Carigali supplied the pipes. The top coat comprised Propelinas PP, toughening agents and stabilisers, while the adhesive interlayer comprised PP modified with MAH, and a commercial FBE was used directly on the pipe. Standard tests were carried out on coated pipe, for example there was no coating holiday at 25kV, peel strength was 3-times the DIN requirement at 50C and thermal ageing to 2012 showed no embrittlement.

DuPont has a new internal coating for downhole tubing, where there are issues with clogging due to asphaltene, paraffins and scale forming deposits.

StreaMax is based on fluoropolymers and is stable under operating conditions of 260C. A thicker coating (100-180 microns) is recommended for areas with asphaltene or wax and these were tested in an Alberta field at 5800 feet deep. After 21 days the pipes were withdrawn and showed no deposits. In a well with severe asphaltene problems, no cleanups were needed during 6 years of operation, while the reference well requires cleanup every 2 months.

The viscoelastic coating supplied by Kleiss & Co. B.V. is based on polyolefin, impermeable to moisture and oxygen, and adheres without a primer. It has been tested at Charter Coating and on a water pipeline in the Kingdom of Saudi Arabia.

Protective casings around pipelines are subject to corrosion and this can be treated using filler. A good material will be anti-corrosive, water resistant, dielectric, inert and pliable. There are many standards for pipes in the US including Department of Transport (DOT) CFR, PHMSA and NACE. The NACE standard SP0200-2008 describes petroleum-based compounds. Trenton Corporation has provided over 3 million litres of wax filler worldwide: current procedure is to evacuate water, add a corrosion inhibitor and then fill.

One of the complications for the industry is the need for pipe in different global regions. Bredero Shaw has developed a new system whereby a mobile coating plant can be set up rapidly (trade mark Brigden). The plant is packed in ISO compliant containers ready for shipping including conveying, tunnel and cooling towers. Plant 1 was set up in 9 weeks and can coat pipe from 8” to 42” diameter.