March 2016, Vol. 243, No. 3
Features
Ins and Outs of Pipeline Coating
The global pipeline coatings and application services market is worth about $5.5 billion a year, according to Noru Tsali at Ami Consulting. Current market conditions are stormy, owing to low oil prices that depress demand for new pipelines, terrorist activities in Libya, Nigeria and Iraq, financial scandals in Brazil and political opposition to new pipelines in North America.
Factors such as these, Tsali said, affect the rate of pipeline construction and repair requirements, upon which demand for pipeline coatings are inextricably linked.
Steel pipelines are ubiquitous, both on and offshore, dedicated to transporting natural gas, crude oil or petrochemical and petroleum products at high pressures over long distances. Such pipelines are protected against corrosion by both external and internal coating systems.
Internal coating liners are applied prior to installation of virgin pipes or for repairs and replacement pipes. According to Kevin Cato, manager of IntraCoat Pipeline Services, “such linings, depending on conditions, can be applied to 15 to 20 miles of pipeline over two to three weeks.”
The conditions in which pipes are laid vary enormously, but a common variant is temperature, ranging from icy cold to extreme heat. For example, Malaysian state-owned Petronas used Dubai-based specialist firm Anti Corrosion Protective Systems to design and install anti-corrosion linings for its fields in the South China Sea where temperatures reach 120°C.
Common Coating Systems
Five main coating systems are available: three-layer PE (3LPE), three-layer PP (3LPP) and PP (polypropylene), fusion-bonded epoxy (FBE), asphalt enamel and polyurethane (PUR).
Pipeline owners and consultants’ choice of coating rests on a combination of factors, including cost, availability of material, control on handling, transportation and certain technical factors. Three-layer PE (3LPE), three-layer polypropylene (3LPP) and – up to seven layers – PP plus FBE are the most commonly used coatings for new pipes, while for repairs, PUR is the coating of choice.
Three-layer PE coating dominates the global market with a 50% market share, reports Austrian coatings company, Borealis. The 3LPE system consists of an epoxy primer with a high-density (HDPE) top coat designed to operate across a wide temperature range from -45°C to 85°C, able to withstand rough handling and installation practices, making it the coating of choice for the Middle East, India and China – regions accounting for a growing proportion of pipeline projects.
Three-layer PP coating systems are best used with temperatures ranging from 0°C to 140°C and pipes that are placed under extreme mechanical stress. 3LPP system consists of an epoxy primer and a grafted co-polymer PP adhesive that bonds the epoxy primer with a PP topcoat. This coating system has proved itself in offshore pipeline projects, especially in the deeper gas and oil fields of the North Sea, Africa, Gulf of Mexico and the Middle East.
Polypropylene (PP) systems consist of up to seven PP layers and thermal insulating foams with high compressive strength, to prevent collapse, making them ideal for technically challenging deep-sea projects with high operating temperatures and external pressures.
Another system, fusion-bonded epoxy (FBE) is commonly used in the United States, Canada and the United Kingdom, but its popularity is declining in favor of 3LPE and PP systems on health, safety and environmental grounds. For pipeline repair projects, asphalt enamel and PUR systems are commonly used, despite health concerns. The table outlines the merits of the most popular pipe coatings.
| Popular Methods For Coating Pipelines | ||
| Coatings | Advantages | Disadvantages |
| Three-layer PE (3LPE) and 3 layer PP (3LPP) | Relatively low material cost
Relatively low application cost |
Requires application of flame to create adhesion
Application of flame in pipeline environments has traditionally been the cause of workplace fires and explosions Offers limited heat resistance. Maximum 225°F to 250°F. Lacks dimensional stability Offers borderline hardness Provides limited resistance to sulphur, amines, oxygen and other oxidants. |
| Polypropylene PUR) systems | Good for deep-sea projects with high operating temperature and external pressures | Polypropylene is liable to chain degradation from exposure to heat and UV radiation such as that present in sunlight. |
| Fusion-bonded Epoxy (FBE) | Excellent chemical resistance
Better dimensional stability – minimal hysteresis |
Relatively expensive
Material expensive Pipe and coating must be heated to 250°F High labor requirement |
| Asphalt enamel and polyurethane (PUR) | Inexpensive
Better than coal tar Enamel Decreased hysteresis Fast cure |
Poor chemical resistance
Severe temperature limitations No dimensional stability |
| Source: BBC, Paintsquare, Dow Chemicals | ||
Reasons for Internal Coating
Internal coating lining for gas pipelines was first developed in the 1950s to reduce the impact of rough steel pipe surfaces and the build-up of deposits and corrosion products on pipe capacity, operation and pumping costs.
The dangers of pipeline corrosion are illustrated by the recent pipeline ruptures in Louisiana in January, Texas in March and New Mexico in August. The U.S. Department of Transportation Office of Pipeline Safety estimated internal corrosion causes 15% of all incidents occurring in oil and gas transmission pipelines at a cost to the industry of almost $15 billion. Studies conducted in the United Kingdom and the Middle East have reached similar conclusions.
Internal corrosion results from the presence of CO2, water, H2S, chlorides (salt water), bacteria, completion fluids or other substances in the produced hydrocarbon. For example, when CO2 or H2S is mixed with oxygen or water corrosive acids can “eat” the steel. Likewise, certain types of bacteria, often found in producing formations, can attack and destroy steel. Moreover, any of the internal corrosives, separately or in combination, can cause leaks and severe blowouts.
Kevin Cato, manager of IntraCoat Pipeline Services in Texas, said benefits from internal protective coatings include increased pipeline flow and cuts to energy and maintenance costs.
“[Internal protective coating] reduces the need for inspections and extends the life of the pipeline,” he said.
An internally coated pipework dries faster after hydrostatic testing than an uncoated pipe, thereby allowing faster commissioning of the line. When Statoil used internal epoxy coating, 3M Scotchkote Epoxy Coating EP2306 HF, to its Langeled Gas Pipeline, in the North Sea, it gained increased transport capacity and reduced “pig” wear.
The benefits of coatings also extend to reduced energy costs at pumping and compressor stations. It may be possible to achieve further savings by reducing the number of compressor stations, or compressor size and capacity.
Reasons for External Coating
Internal protective coating of a pipeline is insufficient. Pipelines must also be protected from the surrounding external environment against a variety of dangers arising from soil stress, soil-born chemicals and salt water. Pipelines must be resistant to indigenous bacteria, other flora, wastewater and the chemicals and solvents used in the processing of the hydrocarbons.
Over and above these threats is the need for protection from extreme temperatures. Pipelines can be found in the hot desert, where temperatures often exceed 100°F, or in Siberia, where temperature can fall to -76°F. Conditions in the permafrost regions, where ground temperature rarely exceeds 32°F, result in the use of ground pipeline installations with their own dedicated protective coatings.
New Developments
“In terms of pipeline coating innovation, the low hanging fruit has been plucked,” said Tsali.
However, the drive to lay pipes in ever more challenging environments, such as deep offshore Atlantic and Siberia, or to heat up and pump heavy crude from remote oil fields, has boosted the need for ultra-tough external coating that can withstand high temperatures.
Companies such as thermoplastic coating technologies Plascoat Systems Ltd. have developed new coatings.
“Plascoat PP10 is an extreme tough coating that meets DIN 30678,” said Plascoat Technical Manager Shoaib Qureshi, of his company’s new coating. “It can be flame sprayed or sintered onto non-linear items such as buckle arrestors, bends, fitting and ancillary items.”
According to Qureshi, it is one of only a few coatings that can obtain a confluent coating between the parent, pipe body coating and the field joint, fitting or bend. This ensures the two coatings react in the same way to thermal, chemical or physical stresses.
Further market pressures are likely to stimulate innovation even further in years to come. Pipe coatings that can heal themselves and return to their former state after being damaged would prove invaluable in remote, deep or inhospitable environments. Meanwhile, researchers at India’s Defence Metrological Research Laboratories see the application of nanotechnology and development of self-healing multifunctional pipeline coatings as the next leap forward.
It will be interesting to see how the pipeline coatings industry commercializes such research in the future.
By Nicholas Newman, Contributing Editor
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