PTFE helps advance critical energy industry requirements
March 21, 2011
PTFE elps advance critical energy industry requirements by Eric Policky
The energy industry as a whole presents an incredibly varied set of challenges when it comes to material requirements. From the temperatures and pressures encountered deep downhole in oil wells to the friction requirements at the top of a wind turbine, material demands are constant only in that they are all stringent.
There are several material challenges within the energy industry which are all particularly well suited to being solved with the use of polytetrafluoroethylene (PTFE). PTFE provides a solution in corrosive environments, high temperatures and situations where a low coefficient of friction is required. It is also used where either electrical non-conductivity or conductivity is required through the use of fillers.
PTFE is a solid, high molecular weight compound consisting entirely of carbon and fluorine. The strength of the carbonfluorine bond as well as the high electronegativity of fluorine gives PTFE several unique characteristics. Neither water-containing substances nor oil-containing substances are wet by PTFE. The polymer is extremely non-reactive and has an extremely low coefficient of friction against any solid. Additionally, PTFE is electrically non-conductive but can be blended prior to processing with conductive carbon while still maintaining the polymer’s other useful properties, meaning PTFE can be used as either an electrical insulator or conductor, depending on the demands of the specific application.
In the area of aggressive media storage and handling, PTFE shines. An example of this is in oil and gas wells, where sour gas (gas containing a significant amount of hydrogen sulfide) or acid gas (gas that contains a significant amount of acidic gases such as carbon dioxide) presents significant handling challenges. Sour or acid gases can be damaging to normal material handling equipment, as acid gases are corrosive and many metals are sensitive to sulfide stress cracking which is promoted by sour gas. In this situation, the fact that PTFE is chemically inert can be a great advantage. Sour and acid gases will not damage a PTFE lining, and will be unable to penetrate the lining to damage any materials underneath it. For this application, the presence of impurities could compromise the ability of the lining by providing a localized chemically reactive area that could lead to an avenue of penetration for the corrosive material. Properly processed PTFE will have very low impurity content, and thus can eliminate this problem. In addition to PTFE’s potential as a lining, it is a great solution for other corrosive material contacting applications such as bearings, gaskets, seals and chevron packing sets.
PTFE has an operating temperature of 500°F/260°C, allowing it to be continuously used at temperatures much higher than most plastics. The high operating temperature allows it to be used in a wide variety of hot environments. For example, natural gas compression can result in a high gas exit temperature from the compressor, and when combined with the possibility of corrosive components in the gas can cause a significant materials challenge. The combination of high operating temperature and chemical resistivity of PTFE can make it an ideal material for seals and even pipe coating in this type of environment. Oilfield service in general presents many of these types of material problems, where high temperatures meet corrosive materials. It is in these environments that PTFE excels.
The continuous machine operation inherent in many energy industry operations makes machine wear a significant area of concern. Possessing an extremely low coefficient of friction is a significant advantage in this type of use, as minimizing friction can help to reduce both energy consumption (through reduced resistance to movement) and machine wear. The addition of fillers to the PTFE can help reduce wear in the PTFE itself, further reducing machine downtime by increasing the wear material replacement intervals in preventive maintenance schedules.
In addition to PTFE’s potential use as a wear material, the flexibility of the material allows it to be used as a diaphragm with a long service life. The high flexibility and chemical resistivity of PTFE makes it an ideal choice for diaphragms with most chemically aggressive media. Additionally, the fact that PTFE is not wet by water or oil-based solutions can help keep pressure losses in a variety of fittings to a minimum.
PTFE excels in the areas of operating temperature, chemical resistance, flexibility and coefficient of friction. These properties allow it to be successfully used in a wide variety of challenging environments common to the energy industry. From the corrosive gases found in many oil wells to the constant motion found in many electricity producing devices, the properties of PTFE allow it to succeed where other materials would fail.
Published in the December/January IAPD Magazine