The application of non-metallic materials is increasingly used in the presence of corrosive fluids in the oil and gas industry. These solutions have an advantage because they can be applied to components already in service, so a sometimes severe damage situation can be overcome.

Polymers, mainly thermoplastics, and composite materials are used worldwide, but often operators are reluctant to endorse their use because they can be quite expensive with respect to carbon steel. However, in the long run savings associated with such solutions can be achieved.

A few applications involving the protective lining of metal tubing and/or pipelines were adopted in ENI facilities. Glass-fibre reinforced epoxy (GRE) fiberglass composite linings were installed inside carbon steel tubings as material for well completions in an oil field located in North Africa (Figure 1), while a polyethylene liner is being installed in a water injection pipeline by means of ‘Swagelining’ technology.

Relining systems are also available in cases when structural properties are requested to be provided by the liner itself, as in the case of an Italian gas field, where they were adopted in 2006. In that case, the liner, resistant up to 368 psi (25 bar), is made of three 0.079-in. layers. The inner layer is usually polyurethane because it is capable of resisting gas with gasoline and water. Polyethylene is used if water only is to be transported. The intermediate layer is made in aramid fibre (Kevlar), and the outer layer is made of polyethylene.

Qualification tests
Before adopting the proposed solution, a characterization program is completed to assess the expected damage mechanisms. All polymeric and composite materials can be subject to physical and chemical degradation when immersed in water and other fluids. Consequently, chemical compatibility with produced and injected fluids as well as production chemicals is a major issue for non-metallic lined pipes.

liner, polypropylene, Eni

Record lengths of polypropylene liner can be quickly installed using the Swagelining process. When pulling tension is released, the liner expands to fit snugly inside the mother pipe.

The evaluation of mechanical properties after exposure is the most useful technique for material qualification. As an example, for composite liners in well tubings the loss of mechanical properties may prejudice other important requirements such as the resistance to external collapse, wireline abrasion, and tool impact.

Accelerated testing at a minimum of three test temperatures, above the likely service temperature, is used to determine the temperature capability of the liner in water, hydrocarbon gas, and crude oil service. EN ISO 2578 provides the principles and procedures for evaluating the thermal endurance properties of plastics exposed to elevated temperature for long periods. The Arrhenius approach described in this standard is used to extrapolate the accelerated data to typical service temperature, demonstrating a steady and predictable loss of properties with time at temperature.

To date, using a three-point bend test in general accordance with BS EN ISO 178 has been the most successful method for applying this method to composite liners. An end-of-life criterion must be selected to allow service life assessment, e.g., minimum stress at break of 14,504 psi (100 MPa) at a particular temperature. Service life assessment in any given application shall take account of prevailing downhole conditions over the life of the well.

Oil field well completion
Before investigating the applicability of non-metallic materials, the wells in this oil field were completed with carbon steel tubulars. Because of high CO2 concentration, high salinity, and high water cut, the wells frequently suffered from corrosion failures. Use of GRE internal liners was considered the best option due to its outstanding resistance to CO2 corrosion, the improvement in flow efficiency given by the smooth surface, and the cost-effective installation of this material compared to stainless steels or the costs of frequent workover activities caused by the failures.

The well temperature was up to 172°F (78°C), well below the maximum allowed for this fiberglass material, which is 248°F (120°C).

The capability of a composite-lined product was proven by the combination of materials tests and system tests. Successful completion of these tests has been judged by the industry to provide a robust technical justification for the application of such products. Flare (liner end protection) materials also must be demonstrated to a capability the same as, or better than, the liner.

After installation, the feedback from the field was that the liner was completely successful: the system performed as expected without failures and, after inspection during a monitoring activity, the liner was in good conditions. An estimate of the obtained savings was also made.

Seawater pipeline upgraded for water injection
A polyethylene-lined 24-in. steel pipeline designed to transport raw seawater to injection wells in Africa was being installed. The estimated 37.5-mile (60-km) length was thought to be the longest Swagelining project ever undertaken.

Swagelining technology is a close-fit lining system using high-density polyethylene (HDPE) pipe, type PE100, with an outside diameter slightly larger than the inside diameter of the pipe to be lined. The PE pipe is pulled through a reduction die to temporarily reduce its diameter, thereby allowing it to be pulled into the original pipeline. When the pulling load is removed, the liner pipe returns to its original diameter until it becomes a tight fit inside the host pipe. Inside diamer reduction of the lined pipe is minimal and is usually compensated by the reduction in internal fluid friction.

A section length of about 1,312 ft (400 m) of carbon steel pipe could be processed successfully in about one hour. Another record of this project was the long length of a continuous sections of PE pipe pulled, equal to 2,854 ft (870 m). The connection between two liner sections was achieved by a special welded compression joint with an internal nickel alloy cladding.

Besides the corrosion resistance, HDPE material showed good resistance to flow erosion and solid abrasion. In presence of sand, which is possible when the filtering system malfunctions, the abrasion resistance of HDPE is higher than the steel (see J.B. Goddard, Abrasion Resistance of Piping Systems, Technical Note 2.116, 1994 and GPS PE Piping systems, Installation and Technical Guidelines, www.gpsuk.com).

Gas field network enhancement
A different type of relining was applied in a section of the pipeline network of an old gas field in Italy, where corrosion problems caused a reduction of mechanical properties of the pipelines. The selected technology has been applied since 2004. It consists of a three-layer internal pipe as previously described (0.079-in poly/0.079-in Kevlar/0.079-in poly).

Due to the conditions of the mother pipe, the composite liner has been specified to have structural properties in order to increase the reliability of the line. The high mechanical resistance of this material is achieved thanks to the use of Kevlar fibers, which have a higher strength than glass.

The maximum design temperature for this line was 122°F (50°C), while operating temperature was in the range of 41 to 77°F (5 to 25°C).

New technologies available
The application of innovative materials is a challenging task because it involves new approaches, new standards, new manufacturers, and new contractors. However, many new technologies of real interest are available, and their use is going to be more widespread due to their ability to solve many operating problems at a reasonable cost.