scope:

Introduction

The maximum allowable temperatures for plastic piping systems used for fuel gas distribution are defined by Part 192, Transportation of Natural Gas and Other Gas by Pipeline: Minimum Safety Standards, Subchapter l), Pipeline Safety, of Title 49, Transportation, of the U. S. Code of Federal Regulations. By an act of Congress, the U. S. Department of Transportation regulates pipeline safety.

Section 375, Service Lines: Plastic, of Part 1.92 of the U. S. Pipeline Safety Regulations allows the use of properly designed metal-sleeved plastic riser pipe. A point that must be considered in proper design is the maximum temperature that can develop in the above-ground portion of the metal riser and its effect on the strength properties of the plastics gas carrier pipe. Section 121, Design of Plastic Pipe, of Part 192 limits the allowable operating temperature of a thermoplastic pipe to the highest value for which the pipes long-term hydrostatic strength has been established, except that it may not exceed 140°F.

There has been some concern that the portion of a plastic riser pipe that is brought up out of the ground inside a protective metal sleeve for connection to a gas meter located outdoors may experience considerably higher temperatures than buried pipe, possibly even above the 140°F limit. Since metal-sleeved risers may be exposed to direct sunlight, they could become heated to higher than ambient temperatures. This report presents test data showing the maximum temperatures that may be obtained by thermoplastics pipe installed inside a metal protective sleeve and the conditions under which the maximum temperatures occur. The report includes:

A description of the test equipment, the environment, and the results obtained when evaluating for the effects of:

a. wall contact;

b. venting;

c. shading;

d. various insulating materials;

e. geographical location.

A correlation of actual and estimated service riser temperatures across the U.S.A.

An evaluation of the influence of temperature cycling on the hydrostatic strength of polyethylene pipe.

A description of a plastic-pipe/metal-sleeve riser assembly design that minimizes temperatures in the plastic pipe.

A list of plastic pipe materials that can be operated safely at the temperatures encountered in a properly-designed service riser.