Polyethylene (PE) is the most commonly applied liner material and one of the most widely produced plastics in the world (tens of millions of tons are produced worldwide each year). PE liners should not be exposed to operating temperatures above 60 °C in water service. In hydrocarbon service (combined liquid and gas phases), the recommended maximum operating temperature is lower and depends on the fluid composition but should not exceed 50 °C.

Polyethylene is a lightweight, durable thermoplastic with variable crystalline structure. Polyethylene is used in applications ranging for films, tubes, plastic parts, laminates, etc. in many markets (chemical, oil & gas, packaging, automotive, electrical, etc.).

Polyethylene is made from the polymerization of ethylene (or ethene) monomer. Polyethylene chemical formula is (C2H4)n.

Polyethylene Molecular Structure.jpg

For lining applications in the energy industry, three types of PE are used; in increasing order of strength and chemical resistance, they are:

  • Medium-density polyethylene (MDPE), used in low-pressure water and gas distribution applications;
  • High-density polyethylene (HDPE), used in all types of service;
  • Ultra High Molecular Weight (UHMW-HDPE) used in demanding applications.
PE (MD) PE (HD) PE (UHMW)
Density (g/cm3) 0.926-0.94 0.941-0.965 0.989
Tensile properties at 23 °C
Yield strength (MPa) 18 25 32
Stress at break (MPa) 20 20 25
Elongation at break (%) >400 >400 >400
Modulus (MPa) 400 700 1100
Thermal conductivity (W/m.K) 0.35 0.4 0.4
Coefficient of thermal expansion (1/K) 200 x 10^-6 200 x 10^-6 200 x 10^-6
Mechanical properties (function of temperature) 23 °C 40 °C 60 °C
Modulus (MPa) 400 250 130
Poisson ratio 0.35 0.38 0.4
Mechanical properties (function of temperature) 23 °C 40 °C 60 °C
Modulus (MPa) 700 450 250
Poisson ratio 0.35 0.38 0.4

PE (UHMW)

Mechanical properties (function of temperature) 23 °C 40 °C 60 °C
Modulus (MPa) 1100 600 400
Poisson ratio 0.35 0.38 0.4

In addition, Polyethylene (PE) is also available in other types such as:

  • Very-low-density polyethylene (VLDPE)
  • High-molecular-weight polyethylene (HMWPE)
  • Ultra-low-molecular-weight polyethylene (ULMWPE)
  • Chlorinated polyethylene (CPE)