Welding Details for Welded Steel Wye Branches

Welded steel wye branches are a key component of most water projects where flows must be divided. They are also a specialty item that requires many engineering considerations. The design of wye branches has been studied by many agencies over the years and good design guidance can be obtained from several sources including the American Water Works Association's (AWWA) Manual M11, Steel Water Pipe: A Guide for Design and Installation, where the focus is determination of proportions of steel reinforcement necessary to resist internal pressure. However, welding details for wye branches is often left to the fabricator, and little guidance is offered. Selection of proper welding details requires a high degree of skill on the part of the fabricator to complete the design and to make it function reliably as a safe, integral part of a conveyance system as intended by the designer. Welding details for complex pipe fittings such as wye branches are not published elsewhere, and fabricators are on their own to make these structures work; there is no common methodology for analysis and design of groove welds that are key structural components of wye branch crotch plates. Often welding details are left to the poor welder actually doing the work, but most welders are not engineers so owners of wye branches end up with "potluck" without adequate engineering oversight. The author is aware of failures attributable to faulty welding details. This paper will address several areas of wye branch fabrication that are not well covered by other sources including local dihedral angle and groove weld bevel determination and weld joint detailing. Weld joint geometry is complex and graphs for determining local dihedral angles for common 90 degree and 45 degree pipe intersections are presented as an aid to the designer of wye branches.