An evaluation of joint repair methods for cast iron natural gas distribution mains and the preliminary development of an alternative joint seal

Abstract

Approximately 10 percent of the natural gas pumped into distribution systems is unaccounted for. A significant portion of this amount is leakage from joints in 50 to 100 year old cast iron main. Because of the cumulative effects of many small leaks, these leaks must be repaired even though the repair expense is not always justified by the value of the gas conserved.

Part One identifies and evaluates leak sealing techniques of the past and present by compiling available test data. A major task was to review all documented test results in journals and technical reports. This study followed-up on published articles by contacting all the individuals and organizations concerned. Recommendations for future development of an alternate sealing system are made.

Part Two discusses preliminary criteria for the design of an alternative system to seal main joints from within the main without service interruption. Experiments were performed showing that very soft elastomers pressed against the rough pipe wall could prohibit leakage. Potential cleaning methods were tested. Wire and abrasive wheels, and water-jets were recommended for further development. Based on time-dependent characteristics and resistance to aging and to chemicals found in mains, fluorocarbon was recommended for use as the seal material. Preliminary design of the seal verified its feasibility. Several innovative concepts for the seal are presented. Considerations for the cleaning and sealing device and for the overal'. system are discussed.