Safety relief manifold

Safety relief systems are verified as part of PSM. This includes the PS Vs themselves and also flare system piping networks. Safety relief valves are covered in Section I—Fluid Flow. A good procedure for sizing the flare system piping is found in Section 19—Safety-Relief Manifolds. This method, first published in the Oil and Gas Journal, has been adopted by APl. I have also used... 

Figure 7-11. Safety valve and rupture disk installation using pressure rupturing disk on inlet to safety relief valve, and low pressure disk on valve discharge to protect against back flow/con-osion of fluid on valve discharge side, possibly discharge manifold. By permission, Fike Metal Products Div., Fike Corporation, Inc.

Where conventional Safety Relief Valves are used, the relief manifold system should be sized to limit the built-up back pressure to approximately 10% of the set pressure... 

This section describes the requirements for the design and installation of pressure relief valve inlet and outlet piping manifolds and valving, including safety valve and flare headers. 

For conventional valves, pressure drop or variations in back pressure should not exceed 10% of set pressure. Because most process safety valves are sized for critical pressure conditions, the piping must accommodate the capacity required for valve relief and not have the pressure at the end of vent or manifold exceed the critical pressure. Designing for pressure 30% to 40% of critical w ith balanced valves, yields smaller pipes yet allows proper functioning of the valve. The discharge line size must not be smaller than the valve discharge. Check the manufacturer for valve performance under particular conditions, especially with balanced valves w hich can handle up to 70% to 80% of set pressure as back pressure. 

For compressible fluid flow in plant piping, one can use Mak s Isothermal flow chart (Figure 1). Mak s chart was provided originally for relief valve manifold design and adopted by API. The relief valve manifold design method, and its derivation, is discussed in Section 20, Safety. Mak s methods can be applied to other common plant compressible flow situations. 

HIPS are critical safety systems, essentially replacing pressure relief and/ or flare systems. These systems are used to provide overpressure protection and/or flare load mitigation for process equipment, pipelines, wellhead flowlines, gas manifolds, or other special purpose applications. Technically HIPS is a safety instrumented function that consists of a set of components, such as sensors, logic solvers, and final control elements (e.g., valves), arranged for the purpose of taking the process to a safe state when predetermined conditions are violated. The HIPS shall operate independently and be completely separate from the basic process control system (BPCS). 

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