Bolt Strength in Sectional Body Construction of Valves

Abstract

ASME B16.34-2017 Section 6.4.2 provides requirements for valves with bolted body joints and threaded body joints. The section states that valves with bodies of sectional construction such that bolted or threaded body joints are subject to piping mechanical loads in addition to the pressure rating for which the valve is designed, shall satisfy the following requirements. For bolted joints, the requirement is a simple formula where the product of pressure rating class designation and ratio of area bounded by the effective outside periphery of a gasket or O-ring or other seal-effective periphery and total effective bolt tensile stress area are less than a certain constant. For bolts of strength less than 137.9 MPa, the value of constant reduces as a multiple of 50.76 times the bolt tensile strength in MPa required or provided in a sectional construction. Section 6.4.3 cautions that the minimum requirements of ASME B16.34 may fall short in scenarios due to valve design, special gaskets, high temperature service, creep characteristics, etc. This paper reviews and studies this ASME B16.34 requirement, which was triggered by failure of a valve with section body construction in the field. Traditionally, valves have been considered as rigid bodies when analyzing a piping system for stresses, support loads, terminal point loads, and deflections. The rigid modeling assumes that the strength of the valve is much higher than an equivalent straight length of pipe. Some computer programs have a provision that permits modeling the valve as a multiple like three- or four-times pipe section modulus. This paper compares the strength of piping and valves based on inherent valve body thickness, body sectional bolting provided, and strength of the equivalent piping flanges. The paper provides conclusions for the user to be aware of so that pre-emptive actions can be taken when using valves with sectional body construction.