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Title: Polyethylene Piping Systems Gas Distribution Service- Retention Of Performance Properties
Author: Karel G. Toll
Source: American Gas Association 1985
Year Published: 1985
Abstract: System Stress. The stresses on buried polyethylene (PE) gas distribution systems are the result of two continuous loads: Cias Pressure load Secondary loads Gas pressure results in hoop stress in the pipe wall which can be accurately calculated. In addition, gas pressure results in stress in fitting joints at changes in section thickness. These stresses, which can be estimated by Von liscs calculations, can be greater than the stress in the pipe wall. It is also important to recognize that notches ai the fusion bond areas act as stress risers resulting in points of localized stresses higher than calculated stresses. Secondary loading will add to stresses from gas pressure. The added streses from secondary loads result from: Deflection from earthload Bending at joints Point loads from rock impingement Axial loads from soil subsidence Axial loads from thermal contraction Good fitting design, field fusion practice, and installation technique can minimize the effect of these stresses in fittings and at fusion joints. Material Strength. The material strength properties of polyethylene must resist these stresses in the system from pressure and earthloads. These material properties include longterm burst strength, and, most important, resistance to crack initiation and crack growth. A great deal has been written on this topic, including the references cited in this report, and will not be covered further here. The rest of the report will discuss an important part of reliable performance of PE gas distribution -the protection and retention with time of basic material strength properties.

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