technical article | Pipe lining Test Sour Sweet
H2S Temp Duration Pressure % (˚C)
2 0
100 100
(days) 339 373
• Long-term stability of Solef PVDF in water, salt, oil and gas. Testing performed at MERL, UK
• Norsok Oil M710, water with sodium chloride at 150,000 ppm Cl
Figure 1: The long-term test performed took one year and was performed in a mixture of oil, water and hydrogen sulphide. Two tests (“sweet” and “sour”) were performed in parallel. The sweet test was performed in order to better assess the effects of the H2S on the long-term properties of Solef PVDF. 2% H2S concentration was defined by the JIP participants, 100˚C was determined also considering the tendency of the hydrogen sulphide to dissolve in the oil by increasing the temperature. The H2S was re-filled every two weeks to be sure to
have a min and constant % inside the autoclaves. Source: Solvay Specialty Polymers
examples in figures 1 and 2). The principle of the Swagelining technique (developed by Swagelining Ltd) is to reduce the size of a polymer pipe by drawing it through a reduction die and maintain- ing the tension under load during installation through the host pipe. Upon load removal, the liner is allowed to revert naturally enabling a tight compressive fit within the host. The technology for polymer lining of subsea water injection pipelines is well established, with inherent reliability proven through successful completion of around 30 projects with no reported in-service failures. Further evidence is demonstrated in a polymer lined
spool piece that had experienced 13 years subsea service in the North Sea at 290 bar[1]
. After long term exposure,
there was little or no corrosion of the carbon steel (a maximum wall thickness loss of 0.28mm was measured) while the mechanical properties of the PE80 polymer liner had remained essentially the same as that of the original material. This proves that corrosion protection is effective when liner systems are used correctly. To date, subsea use of polymer lining has largely
Right: diameter reduction of a PE100 liner during
swagelining of a 330mm
diameter steel pipe
been restricted to PE materials in the relatively benign environmental conditions of low temperature water injection. The fundamental conditions that drive the limits of the service envelope for a polymer liner are the change in mechanical properties due to compatibility with the operating fluids as temperature is increased. Selecting the right polymer is essential. Polymer lining technology demonstrates its competi-
tive price when compared with increased corrosion allowance or corrosion resistant alloy alternatives. Although engineering polymers are more costly than PE, carbon steel pipe lined with Solef PVDF remains cost competitive when compared with metallic alternatives. So why are polymer-lined steel pipes not used more
30 PIPELINE COATING | November 2012
(bar) 60-70
Vapour
frequently? PE has an extensive track record for use in pipelines and extraordinary growth has been seen both for its use in stand-alone pressure pipes and liners over the last 30 years. Due to its inert nature, PE has been successful in applications as diverse as transportation of water, waste-water, gases, oils, multiphase hydro- carbons and mining slurries. However, there have been cases where the polymer has been specified beyond its operational limits. The critical design property which controls the
service envelope is collapse resistance. There have been instances of collapse in service hampering progress of the technology. For hydrocarbon applica- tions, liner collapse resistance must be sufficient to overcome any gases in the transported fluids permeat- ing through the liner and causing expansion of the annular space between the liner and the host pipe during a depressurisation event. There are hydrocarbon applications such as heavy oil
transportation and produced water reinjection (PWRI) where only very low levels of gas are present. In these instances, polymer liners can be designed to withstand the maximum theoretical annular pressure that could lead to collapse without the liner wall becoming uneconomically thick or requiring the need to vent. A number of low-gas hydrocarbon applications exist
where polymer lining already has long service experi- ence, providing an opportunity to increase use either with existing technology or by small incremental step changes. Liners transporting heavy crude oil have been operating successfully in South America for many years and production fluids have been present in water injection lines without detrimental effect. The use of PWRI, where water recovered from
production fluids is co-mingled with seawater, is becoming more frequent as awareness of the need for minimising environmental impact increases. In this application, hydrocarbon species from the produced water are being introduced into the transported fluids
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