Design and Application of AWWA Steel Ring Flanges

Flanged connections have been used on steel water pipe for approximately 100 years and were required for the installation of flanged appurtenances, such as valves, into the piping system. These rolled angle or plate flanges were not manufactured to any official standard and were riveted to the pipe barrel. As the use of steel pipe for waterworks service increased, the need for standardization of flanges increased in importance. Prior to 1950, steel flanges were designed to ASME standards. Flanges complying with these ASME standards were manufactured to dimensions that had a minimum pressure rating of 275 psi, which is in excess of pressure requirements needed for most drinking water supply purposes. In 1945, the ASME and the AWWA established a committee to develop a standard for steel flanges for use in the waterworks industry that were compatible with the pressures, temperatures and dimensions normally encountered in water supply piping systems. Ultimately the report findings, issued by the joint committee in the early 1950's were published as AWWA C207-52T, Tentative Standard Specification for Steel Pipe Flanges. This standard was revised in 1955, 1978, 1986, 2001 and 2007, which represents the current edition of the AWWA flange standard. In addition, a companion AWWA Standard C228 for Stainless Steel Flanges was approved in 2008. Each of these standards includes tables listing various sizes and pressure ratings of both ring and blind flanges along with dimensional information. Embedded in each standard is information related to the design approach used to determine the flange dimensions for the rated pressure conditions and the associated allowable stresses. During the latest revision to AWWA C207, and during the development of AWWA Standard C228, questions were presented relative to the design basis for AWWA steel ring flanges. The discussions presented during this revision period focused on dimensional, primarily flange thickness, differences between AWWA and ASME steel ring flanges. Members of both the Steel and Stainless Steel Pipe Committees convened a special task force to evaluate the concerns expressed during the revision process and to retrieve/evaluate the original design data from the late 1940's and early 1950's. The evaluation revealed two important technical findings, the flange dimensions as published in the two AWWA flange standards were confirmed, and the pipe wall thickness is a critical component relative to flange stresses.