From time to time, we are re-posting particularly well-received articles that have previously run on VALVEMagazine.com so that those who might have missed them will be able to catch up on the best of the best. This article, Understanding and Selecting Valve Flanges, Pt. I: Design and Standards, was Number 2 on our Top Ten online Stories of 2014 and initially ran on November 14, 2014.
Because flanges allow the assembly and maintenance of system components without the need for cutting and welding pipe, they play an important role in piping systems. However, the structural integrity and leak tightness of waterworks piping systems are only as strong as the weakest element, which often is the flange connection between various valves and fittings. Yet because piping systems are subject to many types of loads and are constructed of a variety of materials, understanding and predicting the rating and performance of those flange connections is difficult. This is further complicated by the fact that different sealing mechanisms such as gaskets, O-rings and mechanical seals can significantly affect the performance of the connections. As far as ratings, ASME B16.1 lists pressure ratings for Class 125 flanges from 50 to 200 psig depending on size, material and temperature.