Tangent Outlet Design for Welded Steel Pipe

Tangent outlet fittings are a key component of many pipelines. These fittings are typically used in water-works applications where complete drainage of a pipeline is desired or at pumping stations where necessary for the elimination of air that is troublesome to pumping equipment. Tangent outlets, because the branch pipe centerline is asymmetric with the main pipe centerline, are more complex geometrically than conventional nozzles and tees that are symmetrically oriented. The reinforcement of openings and stress analysis of tangent outlets has not been the topic of many texts. Also, welding details that are critical to the success of any steel fabrication are often ignored. Some design guidance can be obtained from several sources including the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC), Section VIII, Division 1 and the American Water Works Association (AWWA) Manual M11, Steel Water Pipe: A Guide for Design and Installation, however the analysis and design details of tangent outlet fittings for water-works applications could use some improvements for use in the design office. This paper will address the fundamentals of design and fabrication of tangent outlet fittings for welded steel pipe and will explore the geometry and mathematics of typical fittings. The paper will also present welding code concepts and formulas that govern design. In addition, suggested welding details for ease of fabrication will be presented. The goal of this paper is to provide a useful tool to pipeline designers who may have struggled in the past with design issues related to tangent outlet fittings. An example problem is included.