Analysis of Microscopic Leaks in Polyethylene Gas Distribution Piping. TopicalReport, January 1993-January 1996

摘要

The objective was to determine the cause of tiny holes (5 micro m to 50 micro m)found in polyethylene (PE) gas distribution piping in service, with the intent of reducing the number of leaks and thereby the operational costs. Since 1993, United Cities Gas Company (UCG) in Tennessee has discovered gas leaks that were traced to small holes that traversed the pipe wall approximately radially. These holes are smaller by an order of magnitude than other small holes known to occur in PE tubing because of electrostatic discharge. The pinholes were examined and characterized both physically and chemically, followed by experimental attempts to reproduce the pinholes. The causes of the pinholes could not be proven statistically, and the occurrence could not be reproduced in a controlled environment. However, evidence suggests that the pinholes occur because of a progressive breakdown in the electric resistance of the PE under a static electric field which is smaller than that necessary for instantaneous discharge to occur.