Small Diameter Clay Sewer Pipe O&M Strategy: Replace It Now or Run It to Failure

Clay sewer pipe installed prior to 1955 used oakum and cement mortar, tar, or hot sulfur to seal the joints. These materials have not performed well over time. Maintenance data from the Central Contra Costa Sanitary District in Martinez, California, was analyzed to determine the relationship between cleaning frequency and age for small diameter clay pipe. The clay pipe performed reasonably well for the approximately 35 years. After 35 years in service, the required cleaning frequency increased as the joint materials failed. In addition, root intrusion accelerated the failure of the pipe. It appears that the joints had fully failed at 50 years. This finding is supported by evidence from observations made during routine repairs. This finding contradicts the literature values of 90 to 120 years for the life expectancy of clay pipe.Industry standards, regulatory requirements (and penalties), escalating property damage claims, and public concerns about exposure to sewage-borne pathogens are causing the costs of operating and maintaining aging sewers to increase. Prior published life cycle cost estimates have only considered the cost of periodic cleaning which appears to be less than 30% of the actual cost of O&M.This paper will present an overview of clay pipe service issues, the results of the maintenance data analysis, and a cost model, based on actual maintenance data, for use in evaluating the real cost of continuing to maintain a pipe segment compared to the cost of replacement. The decision to replace now (or soon) will be discussed in light of current and future costs and SSO standards.