Performance Characteristics

Polyethylene Resins Continue to Improve
DriscoPlex® 6400 series pipe and fittings for oilfield and energy applications are made from polyethylene materials that are engineered for high density, extra high molecular weight and broad molecular weight distribution. These characteristics give Driscoplex® 6400 series products strength, flexibility, toughness and durability. Since the introduction of polyethylene piping materials in the 1950’s, polyethylene resin manufacturers have continually improved the resins produced. In 2005 “high performance” polyethylene pipe materials were adopted in U.S. ASTM standards. One of the new material designation codes refer to PE4710. Compared to PE3408 (now PE3608) materials, the PE4710 resins have increased density, higher tensile strength and higher resistance to slow crack growth. These increased properties allow the pipe to meet higher performance requirements.

Performance Pipe now manufactures all pipe and fittings of high performance PE4710 resins. Performance Pipe’s PE4710 materials are listed in PPI TR-4 with a Hydrostatic Design Stress of 1000 psi at 73°F. PE4710 materials are an improvement in resin properties and exceed the proven good long term performance of PE2708, PE3408, PE3608, PE3710 or PE4708 pipe and fittings.

PE4710 pipes meet and exceed the physical and performance properties of all the previous material designation codes between PE3408 and PE4710.

API 15LE “Specification for Polyethylene Line Pipe (PE)” recognizes the higher performing PE4710 materials and allows higher operating pressures as compared to PE3408 materials. Refer to API 15LE 4th Edition 2008.

Cell Classification
ASTM D3350 “Standard Specification for Polyethylene Plastics Pipe and Fittings Materials” provides a cell classification system that covers the identification of polyethylene materials for pipe and fittings. Performance Pipe’s Driscoplex® 6400 series cell classification is listed.

Table 1: Cell Classification
Material Designation Code (MDC)

Slow Crack Growth (SCG) Resistance
Resistance to slow crack growth is a critical performance requirement because long-term stress can cause cracks to grow slowly through polyethylene pipe resin material. Resistance to slow crack growth is measured using ASTM F1473 “Standard Test Method for Notch Tensile Test to Measure the Resistance to Slow Crack Growth of Polyethylene Pipes and Resins”. Driscoplex® 6400 series products exceed the requirements of ASTM D2513 that requires that all PE materials meet a minimum of at least 100 hours for two tests before failure when tested per ASTM F1473.

Table 2: Typical PENT Value

Permeability and Permeation
Plastics are permeable to gases to varying degrees. Although some constituents of natural gas can permeate through polyethylene, the volume of gas lost through permeation is generally so low as to have an insignificant effect on the handling of natural gas in a piping system. Other constituents of natural gas are typically heavier than methane, thus less permeable through polyethylene. Hydrogen is the exception; however, the concentration of hydrogen in most natural gas is so low that the actual amount of hydrogen permeation is insignificant. At low temperatures and higher pressures, heavier hydrocarbon gases such as propane or butane may condense and liquify in the pipe. Such condensates are known to permeate polyethylene pipe. Liquid hydrocarbon permeation can affect butt fusion joining. Driscoplex® 6400 piping that has been in service conveying liquid hydrocarbons or wet natural gas that includes heavier hydrocarbons can sometimes exhibit a bubbly appearance when re-melted for heat fusion. This bubbling is the result of the rapid expansion (by heat) and passage of heavier, adsorbed hydrocarbon gases through the heated and molten polyethylene material. Since there currently are no field tests to readily determine the amount of adsorbed hydrocarbons in PE pipe and their potential effect on the fusion joint, the heat fusion process should be abandoned and mechanical connections are recommended if bubbles are encountered during a heat fusion process.

Vacuum or Suction Pipelines
Typical cases of vacuum or suction pipelines are gravity flow, downhill siphon lines, pipelines which are cleaned by vacuum, and gas gathering lines operating under vacuum. When Driscoplex® 6400 series is used in vacuum applications, a sufficiently heavy wall pipe must be selected to resist the collapsing forces. The amount of vacuum a pipeline can support is a function of its dimension ratio (DR) and other operating conditions. A thicker wall pipe will provide a greater resistance. Refer to API 15LE “Specification for Polyethylene Line Pipe (PE)” Appendix B or the Plastic Pipe Institute “Handbook of Polyethylene Pipe,” Chapter 11, for more detailed information on vacuum or suction lines.

Chemical Resistance
Driscoplex® 6400 has outstanding chemical and corrosion resistance and will tolerate most downhole corrosion inhibitors, hot soils and sour gas. It has proven use in crude oil service, low-pressure gas operations, acidic or alkaline water service and brine service. Dry, gaseous hydrocarbons have no adverse effect on expected service life. Liquid hydrocarbons will permeate the wall and reduce hydrostatic strength, but normally will not degrade the material. A technical report of chemical resistance for thermoplastic pipes can be found at the Plastic Pipe Institute’s website: TR-19/2007 “Chemical Resistance of Thermoplastics Piping Materials.”