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HDPE Copolymer Liner

Melt Index

2

ASTM D 1238

6.5 g/10 Minutes

Vicat Softening Point

ASTM D 1525

259ºF

Brittleness Temperature

ASTM D 746

< -180ºF

Density

ASTM D 4883

0.944 g/cc

Hardness (Shore D)

ASTM D 2240

66

Environmental Stress Crack Resistance3

ASTM D 1693

> 2000 Hours

Environmental Stress Crack Resistance4

ASTM D 1693

> 5000 Hours

Notch Tensile (PENT)

ASTM F 1473

> 100 Hours

Notched IZOD Impact Strength (23ºC)

ASTM D 256

6 ft-lbf/in

Cell Class

ASTM D 3350

PE 345464C

The HDPE copolymer liner is a non-structural fluid barrier for the containment of liquefied petroleum gas (LPG). It consists of a high-density polyethylene (HDPE) copolymer. By virtue of its low modulus, the liner transfers all loads to the composite shell. The plastic liner is an assembly of two injection-molded heads and an extruded pipe section joined together by butt fusion welds. Nominal wall thickness of the liner is 0.50 inch. This relatively heavy wall thickness is needed due the stiffness required from the liner during the winding process, when the liner serves as the winding mandrel. This method of liner construction was selected because of its high reliability and resistance to permeation and leakage. Typical property values for this material are provided in Table 3.

An aluminum end boss is inserted into each liner head. The boss at the service end provides a single penetration into the tank for vapor service, filling, liquid level gauging, and the safety relief valve flow path. The boss at the non-service end serves a tail-stock-type function during the fiber winding process as well as providing structural support at confluence point of the fibers over the head. A circumferential keyway in the boss flange provides the mechanism for insert molding the end boss into the liner head. The flange keyway is coated with a thin layer of elastomeric material which serves as a low pressure gasket. The interface is purely mechanical, and is designed such that there is no tendency for the plastic to creep under pressure. This interface is further described in U.S. Patent 5,429,845.

1

2% Secant-Method 1

3

16 kg 3 Condition B, 10%

Table 3. Typical Properties for the High-Density Polyethylene Copolymer

2

190 C

4

Condition C

Value

3300 psi

  • >

    800%

120 ksi

Property Tensile Strength at Yield (2 in/min) Elongation at Break (2 in/min)

Flexural Modulus

1

Reference ASTM D 638 ASTM D 638

ASTM D 790

Alternative Underground Propane Tank Materials, Phase II—Final Report

8

September 2009 Battelle and Lincoln Composites

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