Optimizing Bolting Configurations in a Pressure Vessel

Abstract

Abstract Control valve standards and guidelines (specifically ASME B16.34), which have been in place for over 50 years, have undergone incremental changes. These standards are important as they prevent field failure by maintaining system performance and ensuring the safety of workers and other components in proximity to valves. New control valve technologies represent a significant alteration in valve geometry and operating characteristics. During the development, the valve body geometry and design requirements were closely examined. The authors have identified opportunities for adjustments to ASME B16.34 design requirements through the review of related standards and the process of design optimization. Specifically, this paper reviews the design requirements for valve body joints and their bolting configurations. It examines bolt properties, including yield stress, proof strength, and allowable stress, through the ASME Boiler and Pressure Vessel Code [1], ASME B16.34 [2], ASME B16.5 [3], and ASME B31.3 [4]. It is proposed that the design requirements found in ASME B16.34 Section 6.4, Valve Joints, be adjusted such that the allowable stress limit for high strength bolts can be fully utilized. Finite Element Analysis is performed to examine those dynamic loading scenarios that are accounted for in the determination of allowable stress - temperature gradients (which cause pipe expansion and contraction), cyclic fatigue, vibration, impact (flashing or hydraulic shock), seismic events, and live loads (ice/snow). Data from the analysis is presented to show that the modified bolting configuration can withstand the maximum pressure and temperature requirements. Alternative bolting configurations can be shown to conform to the allowable stress requirements, allowing for design optimizations that reduce the overall size and weight of a valve. Modifications to ASME B16.34 and ASME B16.5 are therefore recommended. When the proposed bolting configuration was applied to a DN25 valve, we were able to achieve weight savings of 4 lbs., along with a 0.6” reduction in outer diameter. These optimizations allow for manufacturing cost savings including cost of hardware, raw materials, and machining. This optimization can be extrapolated for greater savings with larger valve designs.