Relief manifolds

Mak has developed an improved method of relief valve manifold design. The APT has adopted this method, which starts at the flare tip (atmospheric pressure) and calculates backwards to the relief valves, thus avoiding the trial and error of other methods. This is especially helpful when a large number of relief valves may discharge simultaneously to the same manifold. 

Mak s developed isothermal equation (based on the manifold outlet pressure rather than the inlet) is  

D = Header diameter, ft f = Moody friction factor L = Header equivalent length, ft M2 == Mach number at the header outlet Pi,P2 = Inlet and outlet header pressures, psia 

Z = Gas compressibility factor T = Absolute temperature, °R Mw = Gas molecular weight 

Check all relief valves against their MABP. 

---

Mak, New Method Speeds Pressure-Relief Manifold Design, Oil and Gas Journal, Nov. 20, 1978. 

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... 

Beveridge, H.J.R. and Jones, C.G., Shock effects on a bursting disk in a relief manifold, in The Protection of Exothermic Reactors and Pressurised Storage Vessels, I Chem E Symposium Series No. 85, pp. 207-14 (1984). 

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... 

Beveridge, H. J. R., and Jones, C. G., Shock Effects of a Bursting-Disk in a Relief Manifold, Institution of Chemical Engineers Symposium, Series No. 85. 

Since Mak s Isothermal flow chart is intended for relief manifold design, it supports calculations starting with P2, the outlet pressure, that is atmospheric at the flare tip, and back-calculates each lateral s inlet pressure. Pi. These inlet pressures are the individual relief valves back pressures. The chart parameter is M2, the Mach number at the pipe outlet. Having M2 is very useful in monitoring proximity to sonic velocity, a common problem in compressible flow. 

Note This case (given P2 and W) is the same as an individual lateral in relief manifold design. 

Mak, H.Y., New method speeds pressure relief manifold design. Oil and Gas... 

---