Welded Lap Joint Brittle Failure: A Structural Assessment of an Atlanta 72-Inch Welded Steel Water Pipe Demonstrates Need for Improvement in AWWA Standards

A condition assessment of the City of Atlanta 72-inch buried welded steel raw-water pipeline was performed in 2006 by CH2M HILL/Williams Russell & Johnson Joint Venture Inc. and ATS Inc. on behalf of the City of Atlanta Department of Watershed Management. The pipeline is spiral welded with ½-inch wall thickness and double welded bell and spigot lap joints. It was fabricated in 1973 and 1974 to the standard of "Mill-Type Steel Water Pipe," AWWA C202-64T, Class B. This assessment focused on structural integrity, as the pipeline has a history of numerous failures since entering service in 1975. Past failures have been reported as full-circumferential brittle fractures through the bell at the toe of the internal fillet weld. In-situ and laboratory structural examinations were performed including extensive analyses on a 4.5-foot sample, including an intact bell and spigot lap joint, cut from the 72-inch welded steel pipe (WSP) alignment. This assessment did not include an investigation of an actual failure site. Data from this assessment indicates that the steel is extremely brittle within the cold-formed bell (Charpy V-Notch < 6 ft-lbs at 60° F). Past failures are likely the result of a high concentration of stress in the bell at the toe of the internal lap (fillet) weld of the fully stabbed joint, where the pipe steel is extremely brittle and where welding-induced notches were observed. All failures have occurred during winter months when water temperature is lowest, the steel is most brittle, and thermal induced longitudinal tension is maximized. The authors wish to translate the results of this condition assessment into recommendations—from the consumer's perspective—for the improvement of the industry standards for welded steel water pipe. Although AWWA has made improvements to their standards (M11-2005, C200-1997, and C206-2003) due to lessons learned from other WSP failures, gaps remain within these publications that may allow defects in design, fabrication, and installation of a new WSP.