AMI Consultant Assesses Outlook For Pipe Coating

Noru Tsalic, consultant at Applied Market Information (AMI), has revealed that oil prices are starting to rise again and that the outlook for pipe coating is very encouraging. According to Tsalic, who was speaking at the AMI conference on pipeline coating held in February 2010 in Vienna, Austria, the economic crisis has affected pipeline construction, as with many other industries, because of the lack of availability of finance for new projects and because of the drop in oil-and-gas prices. Russia has the largest natural-gas reserves and is in the top 10 for oil reserves.

Transneft has 49,000km of pipelines and Gazprom has 169,000km of gas transmission systems. The most common onshore coating in the country is polyethylene. The average pipeline lifespan is 33 years and around 34 per cent of oil trunk lines are more than 30 years old, which shows the potential for market growth. In 2007, Exxonmobil was producing the equivalent of 4.2 million barrels of oil per day with seven new upstream projects. Michael Surkein of the development division has reviewed pipe coatings.

Fusion-bonded epoxy (FBE) is used up to +95C, with three-layer polyethylene up to +80C and three-layer polypropylene (PP) up to +110C. Polyurethane is sometimes added for insulation; compatibility with the polyolefin coating then becomes an issue. The company looks at aspects such as handling, cathodic disbondment and the ease of field joint coating. FBE is the main pipe coating in North America and the Anzac, whereas polyolefins predominate in Western Europe, North Africa, Russia and South America.

Canusa-CPS is working on improved coating systems; for example, the PP preheat temperature in the new GTS-PP is down to +160C, with an improved operating temperature rating of +140C. Salzgitter Mannesmann Forschung is a pipe coater; chromium ions are used for the pre-treatment of FBE coatings, but this process may be banned as it is very toxic. The company has recently studied alternative adhesion promoters, including epoxysilane and aminosilane, Ti and phosphating. It is proving difficult to match the performance of chromating.

Wet sour gas is a corrosive hazard in the petroleum industry. Tuboscope/Vetco has an epoxy novolac coating with high hydrogen-sulphide resistance and a maximum service temperature of +204C, primarily for high-pressure, high-temperature (HPHT), sour environments. It is said to be the only coating approved for Khuff Gas/Aramco and has also been tested by Vnigaz/Gazprom. In Brazil, Petrobras has been studying the joints of FBE-coated pipes in the Ubarana pipeline. As the oilfields are ageing, water injection is being used as the standard method to aid recovery, but this increases the corrosion of pipes.

This research has found a successful method of qualification for the water injection Ubarana 12in (30cm) pipeline project with FEB on the girth welds. Dow Coating Materials is producing new high glass transition temperature (Tg) resins for FBE coatings, developed by modelling the molecular structure of epoxy. These are for high service temperature operation and can raise the Tg by up to 50C. New curing agents enable the durability to be extended even further. Akzo Nobel Powder Coatings supplies epoxy for multilayer pipe coating systems and has been developing materials for the deeper wells and extreme operating temperatures.

The mid-Tg FBEs offer flexibility even down to -60C and showed no blistering after two months of exposure to the hot-water gradient test at +80C, unlike standard FBE, which blistered at one week. Stopaq offers viscoelastic coating technology, such as with a wrapping band, then an outer glass shield and a top layer for anti-fouling or ultraviolet (UV) resistance. Liquid epoxy coatings and FBE powers are supplied by 3M's Corrosion Protection Products Division. The company invented FBE about 40 years ago; it has developed a protective network coating (PNC), which is a one-part, heat-curable, thermosetting hybrid coating for the corrosion protection of pipes in three-layer polyolefin systems.

The PNC has an operating window between -50C and +150C. The product has been tested by both 3M and its customer Socotherm Escobar. The offshore industry trend is towards deeper water and longer tie-backs, which expose the limitations of existing pipe coatings in terms of hydrostatic pressure limitations and subsea and chemical stability. Bredero Shaw has developed the Thermotite Ultra insulation system for these conditions. Statoilhydro has reviewed the long-term performance of the thermal insulation of flowlines in the Kristin HPHT field. The company considered a variety of pipelines from bundles with heating/cooling with water to steel pipe-in-pipe with polyurethane insulation.

Various polymers were considered for insulation systems, including polysulphone, polyether sulphone, polyurea, five-layer PP foam, polyamide thermal barrier and five-layer PP, HT rubber, syntactic phenolic foam and syntactic epoxy with a PU outer insulation layer. The polysulphone, polyurea and polyamide systems all suffered from hydrolysis. The syntactic phenolic was not reelable. The five-layer PP foam system was hydrolysis resistant at 160C and was therefore selected; it has been in use since autumn 2005. Borealis supplies PP materials for pipe coating.

It has looked at material performance in more extreme subsea HPHT conditions. Standard three-layer systems for onshore and offshore uses between -20C and +110C use epoxy, adhesive and topcoat. For subsea purposes, the system uses epoxy, adhesive, solid, syntactic PP, barrier, insulation and an outer layer and operates between -20C and +140C. The syntactic PP contains hollow glass spheres to give insulation and has a typical glass content of 25 per cent. It can be used at water depths to 3,000m. An ordinary PP foam layer can be used down to 400m. A strong PP foam, patented to Borealis and exclusively licensed to Bredero Shaw, can be used down to 2,200m.

New coatings have been tested at Thunder Horse in the Gulf of Mexico and Tyrihans in the North Sea. Another new coating system has been developed by Dow Chemical, comprising three-layer technology with black high-density PE top coat and grafted functional polymer adhesive. The HDPE offers high environmental stress crack resistance, good processing and long-term thermal and UV stability. The adhesive was found to be fully compatible with a range of epoxy materials. Arkema is also offering a black HDPE topcoat-adhesive system from Total Petrochemicals that uses polyethylene from. The HDPE is bimodal and has hexene as a comonomer to improve mechanical and environmental stress cracking performance.

The bimodality combines processing with mechanical properties. The adhesive is based on PE grafted with maleic anhydride and has a high adhesion to both PE and epoxy. This system has been produced for harsh operating conditions in the oil industry. Ductile engineered cementitious composites provide mechanical protection for onshore pipelines. They have been studied by Li, Fischer and Lepech and Associates. The polymer binders in this new material were supplied by Wacker, while Bredero Shaw has been involved in the evaluation and coating application. It has been tested as an outer coat for PE-coated pipe and the interface with the polyolefin has been studied.

The most economic application method is side wrapping in a mobile concrete coating plant. It has a lower fibre content than other reinforced-concrete mixes, so it is easier to mix and apply. Dow Hyperlast has a new closed-loop portable continuous mixing plant to generate glass syntactic polyurethane on site. The company claims that this gives a very fast line pipe insulation. The system is being used in the Gumusut-Kakap project of Sabah Shell Petroleum Company. Many pipelines are ageing, so Berry Plastics has studied the durability of coatings.

The company compared three-layer PE, three-layer PP, liquid epoxy, FBE, polyurethane, cold-applied tapes and heat-shrinkable sleeves using extended periods of hot-water immersion (HWI). In 1987, Shell used 120-day HWI testing. The water should be heated to the maximum pipe operating temperature. It is a useful method of testing coating performance. The third AMI international conference on Pipeline Coating will be held on 7-9 February 2011 in Vienna, Austria. Offers of papers should be sent to Dr Sally Humphreys before 6 August 2010.


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