Piping outlet

The size of outlet piping required for a safety disc is not necessarily the same as the disc receptacle size. Discs frequently are sized on the basis of pressure requirements rather than capacity requirements. In such instances it is possible for the outlet piping to be smaller than the pipe size of the disc receptacle. If an arrangement of this type is desirable, the pipe diameter must be calculated on the basis of the relief capacity requirements and the maximum allowable upstream pressure. The inlet piping, however, must have an area which is at least equal to that of the receptacle in order to comply with the ASME code. 

The pressure drop allowed through the inlet and discharge lines is unlimited as long as the capacity of the line is adequate for the relief requirements. That is, at the required flow rate the vessel pressure must not exceed the maximum allowable accumulated pressure. In sizing a safety disc, it is usually assumed that the entrance loss at the nozzle is the governing restriction insofar as capacity is concerned. Thus the effective orifice area is considerably larger than the effective orifice area of a safety valve of the same pipe size. Consequently, 

The allowable pressure loss through the discharge pipe, exclusive of the entrance loss, may be determined as follows  

Pa = Accumulated relieving pressure, psia P = Pressure inside relief pipe near the vessel, psia 

If P exceeds Pare it becomes necessary to size the safety disc based on subsonic flow. 

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A distributor is frequently installed at the top of the column for use during backwash. It collects water evenly and prevents resin from escaping the column should unexpected surges develop in the water flow during backwash. Columns lacking an upper distributor or screen to prevent loss of resin should have an external system to prevent resin from being lost to the drain. It is referred to as a resin trap and may consist of a porous bag that fits over the outlet pipe or a tank designed to lower the linear velocity. Resin drops to the bottom of the tank and is returned to the column when convenient. 

The correclion (Fig- 6-14rZ) accounts for the extra losses due to developing flow in the outlet tangent of the pipe, of length L. The total loss ror the bend plus outlet pipe includes the bend loss K plus the straight pipe frictional loss in the outlet pipe 4fL /D. Note that = 1 for L /D greater than the termination of the curves on Fig. 6-14d, which indicate the distance at which fully developed flow in the outlet pipe is reached. Finally, the roughness correction is... 

FIG. 6-14 Loss coefficients for flow in hends and curved pipes (a) flow geometry, (h) loss coefficient for a smooth-waUed hend at Re = 10, (c) Re correction factor, (d) outlet pipe correction factor (From D S. Millet] Internal Flow Systems, 2d. ed., BHRA, Cranfield, V.K., 1990.)... 

An acid egg, or blowcase, consists of an egg-shaped container which can be filled with a charge of liquid that is to be pumped. This container is fitted with an inlet pipe for the charge, an outlet pipe for the discharge, and a pipe for the admission of compressed air or gas, as illustrated in Fig. 10-58. Pressure of air or gas on the surface of the liquid forces it out of the discharge pipe. Such pumps can be hand-operated or arranged for semiautomatic or automatic operation. 

Specimen Location Outlet piping of a sulfuric acid storage tank... 

T Outlet pipe circulation The coolant is drawn from the surrounding medium but is discharged remotely through the pipes 2 ... 

Inlet and outlet pipe circulation The coolant Hows from a source other than the surrounding medium through the inlet pipes and is discharged remotely through the outlet pipes 3 ... 

One velocity head for inlet and one half for outlet pipe velocity is close. 

For revamps, exchangers with the low-pressure fluid on the tubeside can sometimes be re-rated for the two-thirds rule without any equipment redesign. However, the inlet and outlet piping up to and including the isolation valves may also need to be re-rated or redesigned for the two-thirds rule. 

The 1997 edition of the API RP 521 extends the two-thirds rule to include the upstream and downstream system. At a minimum, the inlet and outlet piping up to and including isolation valves must be designed for the two-thirds rule to be able to block in the exchanger. If the upstream and downstream equipment is not designed for the two-thirds rule, relief devices may be required on both the inlet and outlet piping to protect the piping and adjaeent equipment. 

A check valve is not, however, permissible in PR valve inlet or outlet piping, or in any flare or safety valve header. 

Where outlet pressure losses exceed 10%, bellows valves are often considered. However, substitution of a bellows valve for a conventional valve may not necessarily solve the chatter problem since debits associated with bellows valves reduce the rated capacity of this type valve. Hence, the valve has a tendency to become oversized depending on the amount of back pressure encountered. For this reason, revision of outlet piping to reduce the back pressure within the 10% limit is strongly preferred to the alternative of installing a bellows valve. 

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. 

Piping Restrictions - No restrictions such as check valves, flame arresters, orifice plates, etc., are permitted in the outlet piping. 

Outlet Pipe Sizing - Outlet piping is sized according to minimum diameter and exit velocity considerations, as follows ... 

Design Temperature of Outlet Piping - The design temperature of outlet piping from PR valves discharging to the atmosphere is normally ambient. However, autorefrigeration and need for brittle-fracture-resistant materials or thermal expansion forces should be examined if the release pipe is unusually long. 

PR Valve Outlet Piping - The outlet piping from a PR valve must be at least equal in size to the valve outlet flange. 

Two types of boundary conditions are considered, the closed vessel and the open vessel. The closed vessel (Figure 8-36) is one in which the inlet and outlet streams are completely mixed and dispersion occurs between the terminals. Piston flow prevails in both inlet and outlet piping. For this type of system, the analytic expression for the E-curve is not available. However, van der Laan [22] determined its mean and variance as... 

Geometrieally defined boundaries within one phase aeross whieh exehanges oeeur eidier by bulk flow or by moleeular diffusion (e.g., nutrient inlet and outlet pipes). 

A more sophisticated theory was given by Barth, in which the pressure drop of a cyclone is defined as a function of the swirling velocity head of the fluid in the outlet pipe as follows ... 

Barth assumed that the pressure loss of a cyclone consists mainly of the pressure loss required to overcome the wall friction of the cyclone and the pressure drop to drive the fluid out of the cyclone outlet pipe. This leads to the following expression for the total loss factor C/ ... 

Premature disk failure Operator error Pump motor failure Reaction inliibitor system failure Coolant system failure Outlet piping obstruction Motor alann failure Pressure sensor failure... 

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