How to Reduce Bending Moments on Large Butterfly Valves Belowground

When projects require direct buried installation of large butterfly valves, special installation, factors must be considered to maintain valve integrity, and prevent damage to the pipeline. In response to a request from AWWA’s steel pipe and stainless-steel pipe committee chairs, a task force on large valve installation meeting was first held at ACE17 in Philadelphia to discuss the issue of valve deflection; since then the committee has had multiple meetings and, most recently at ACE19, the task force discussed additional mitigating solutions to limit loading of valves by thereby controlling deflections. One of the solutions proposed by the AWWA task force committee was the addition of grooved, flexible yet restrained couplings on either side of the valve. This paper will address the benefits of the addition of grooved, flexible yet restrained couplings, located on either side of the large butterfly valves belowground. Piping stress analysis, using CAESAR II software that utilizes an FEA analysis using beam elements with 6 degrees of freedom at each node, was performed on 24”, 48”, 72”, and 96” steel pipe sections subject to a rigid restraint on the left, a guided restraint on the right near each side of the valve, 100 psig water pressure, and a 2” vertical displacement. The moments on the fixed end (valve end) were calculated with and without pairs of flexible couplings. When couplings were used, the moment on the valve was reduced by about two-thirds when compared to the case where pipe was installed without couplings.