Steel Water Pipe Joint Testing

Abstract

Steel water pipe in the municipal industry has typically been designed with either restrained or non-restrained joints, (typically rubber gaskets). Restrained joints are required where thrust is at elbows, tees, laterals, wyes, reducers, valves, and dead ends. These joints are restrained by welding, harnessing and blocking. Most typical is the welded slip joint, because of its flexibility, ease in forming and laying, watertight quality and its ability to make small angle changes at each joint. The efficiency of the welded slip joints and rubber gasket joints has been tested by numerous manufactures for internal pressure. The pipe barrel will usually fail by exceeding the elastic limit of the steel prior to leaking or failure of the joint. This is due to the increased section modulus of the joint configuration and stress orientation. The ASME, recommends applying joint efficiencies of 0.45 and 0.55, respectfully for single and double-fillet lap welds and 0.9 for butt-welded pipe. The full-scale tests done by Thompson Pipe and Steel Company (1984) showed efficiencies in the 0.83 to 0.76 range for lap welded pipe. The unpublished tests at Consolidated Western Steel (1958) revealed efficiencies at nearly 1.0 for lap welded joints. Joint efficiency values are sometimes used to calculate shell thickness for buried pipelines. The question arises, what do these efficiencies mean, and how should they used in design of welded joints?