Internal plastic pipe coatings have been in use since the 1940s. Valspar is currently reviewing powder coatings for the oil and gas exploration market, which can extend drill pipe lifetime and improve pumping efficiency by providing a smooth surface. Liquid phenolic coatings offer high temperature and chemical resistance, but contain formaldehyde and organic solvents and release volatiles during cure; they also require several thin layers of coating and are subject to health, safety and environmental restrictions.
Fusion bonded epoxy (FBE) is chemical and temperature resistant, has no volatiles and is applied as one thick coat: this is a growing market. The test method used for internal coatings in this study was NACE TM0185-2006, which is autoclave testing under high temperature and pressure, with water, hydrocarbon and gas phases, rapid and slow depressurisation.
Petroleum Development of Oman (PDO) has worked on a new specification for internal liquid epoxy coatings. There is a shortage of FBE coaters in Oman and other issues over project completion and qualification, so PDO undertook a market study including liquid epoxy coating and FBE. The latter needs a higher application temperature but cures faster and is more flexible than liquid coating. Conditions for oil and gas pipes were assumed to be 85C, 50% water cut, 3 bar carbon dioxide and 0.5 bar hydrogen sulfide.
A search for coating suppliers worldwide followed by testing of materials (ASTM, NACE and PDO, destructive and non-destructive testing (NDT)), narrowed the field to 6 potential products. Although all coatings tested were epoxy novalac based, there was a wide range of performance and the search for a suitable liquid coating is ongoing.
There is a high performance thermoplastic that is now being used in internal coatings, i.e. polyamide 11 from Arkema. The usual application methods are hot spraying or dipping. The polymer is ten times more flexible than FBE and after 5 years of use in a salt water injection pipe there are no signs of degradation or loss of adhesion.
The company has undertaken a study with Cybernetix to develop a robotic system that can undertake internal pipe joint coating. The project sponsors include TOTAL and GDF Suez. The robots are required to blast and clean the surface, apply epoxy primer, heat the pipe and apply PA 11 powder, then cool. This is still under development.
BSR Pipeline Services is a 50:50 joint venture between Tata Steel and Ramco. It provides coating services for Tata Steel Tubes, both internal and external. In one of the latest projects, a new 4-layer polypropylene (PP) coating was applied to a 530m section of a new pipeline in the North Sea, owned by Total E&P and laid by Subsea 7. This system comprises epoxy, adhesive, foamed PP and a topcoat of PP and had to meet a required thermal insulation performance of <6Wm2/K. According to Tata Steel Tubes, the foam layer is customised for each project and depends on factors such as water pressure and the required insulation value.
Polyurethane (PU) foam is another thermal insulation material. BASF has conducted trials to predict long-term ageing of glass syntactic PU in deep sea applications, looking at several potential failure modes including thermal degradation, water absorption and hydrolysis. Samples were immersed in sea water at 80C, 90C and 102C, and the changes in tensile strength were monitored up to 25 weeks. Long-term prediction-extrapolation methods have been compared.
Deep water offshore insulation coating has been evaluated by Bredero Shaw, looking at thermal and mechanical performance. The heat loss coefficient (K-value), specific heat capacity and hydrostatic load response are measurable features of this. The requirements of the application depend on a variety of factors such as temperature and water depth. Chemical ageing and water uptake can both be detrimental to insulation. The company has tested its foamed polymer coatings in simulated service tests.
Det Norske Veritas (DNV) develops safety standards and recommended practice (RP) including DNV OS-F101 on submarine pipelines. DNV has worked with companies like Statoil (Hydro) to adjust standards to improve quality and reliability in the field, which is particularly useful offshore where inadequate coating of pipes and joints can be very expensive to repair after installation. In 2011 two updates will be issued on Submarine Pipeline Coatings, partly for compliance with ISO 21809.
