Self-draining lines

All filling lines should be self-draining. Where this is not possible with residual fuel installations, trace heating and lagging should be applied, and this is particularly important in exposed positions. This will ensure that any oil fuel remaining in the filling pipe will be at pumping viscosity when delivery is made. 

This improves temperature control of the material In the lines and avoids settling of reinforcing materials when they are used. All lines should be designed to be self-draining to simplify machine clean out. Smooth inside surfaced flexible hoses lined with Teflon are preferred where flexible lines are required. Where these lines are jacketed, It is preferred that the jackets be coupled to the suction side of the recirculating oil pumps to keep the oil pressures low. Should leakage occur between the jacket and the reactant streams, then It is more likely that the reactants will leak into the oil than visa versa. Oil contamination will adversely affect nylon RIM reaction speed and physical properties. Many manufacturers of RIM equipment recommend that all tanks, valves and fittings for nylon RIM machines be made of stainless steel. Mild steel and... 

Relief line headers, individual relief lines, blowdown lines and flare lines should be self-draining from all relief valve outlets to the knock-out drum, flare stack or a point at the plant limit. A pocketed relief line system is more expensive, because usually an extra condensate pot is required with instruments, valves and pumps. To eliminate... 

Small quantities of liquid should always be expected in column vapor outlets. The origin of this liquid can either be entrainment from the column (fine droplets can pass even through mist eliminators and coalesce in the overhead line), or atmospheric condensation. Low points in vapor outlet lines should be avoided as these tend to trap and accumulate liquid. The accumulated liquid back-pressures the column, causing instability, erratic operation, and slug flow into the downstream unit one case history where this occurred has been reported (203). Vapor outlet lines should be sloped (i.e., self-draining) ei-... 

Vapor bypass piping and equalizing lines shoiild be self-draining and should contain no low points where condensate can accumulate. 

For removing water floating on a chlorinated hydrocarbon bottom layer, two or three drain valves at easily accessible positions should be provided. The valves should be fitted close to the tank sides to avoid the danger of the drain lines freezing up. Product tanks should be fitted with pressure-vacuum valves and with self-closing dip and sample hatches. 

Piping layouts should be simple and designed for liquid velocity not exceeding 0.6 m/s. The number of valves should be kept to a minimum. The lines shonld be self-draining. 

Traps should be installed below the equipment being drained. If this is not possible, a lift fitting or water seal should be provided at the low point. Discharge lines should be kept short to minimize freezeup damage. Traps should be installed to be self draining. Bucket traps must be protected from freezing and must be protected against loss of prime as a result of sudden or frequent drops in steam pressure. 

Two flow regimes are possible for drain piping self-venting and siphon flow. Liquid in a self-venting line occupies a portion of the pipe cross-section, and gas moves freely with, or counter to, the liquid. Siphon flow refers to a liquid or two-phase downflow where pressure increases in the direction of flow. 

The pressure in vacuum distillation columns with is similarly controlled by manipulating the spillback around the ejectors, as shown in Figure 12.51. The installation of the pressure transmitter needs special attention. It is important that the impulse line is self-draining back to source otherwise a liquid head can build up and cause a false pressure measurement. The liquid may also boil and cause a noisy measurement. 

The value of dT/dP increases as the bubble point of the product increases. We have seen that for LPG, it is typically 3 to 4 °C/bar. For a vacuum column operating at an absolute pressure of 30 mm Hg, with a tray temperature of400 °C, dT/dP will be in excess of 800 °d bar. Under these circumstances it is important that pressure changes are measured accurately. The pressure transmitter should be therefore located close to the temperature measurement so that changes in pressure drop across the column have no effect. The impulse line should be self-draining back to the column to avoid introducing noise into the pressure measmement due to liquid boiling in the line. 

If the water users are located in a structure, the underground portion of the lines should terminate with bevel ends 12 in (300 mm) above grade. Cooling and hot water headers to the pumps are run under the pipe rack, between the rows of pumps, as Exhibit 13-24 shows. A self-draining hydrant valve is used if the installation is in a freezing climate this detail is displayed in item 8 of Exhibit 13-25. 

Usefiil for level measurements, this design is almost mandatory for specific gravity measurements via AP for slurries. It may also be used wirii gas or steam flow-meter installations with self-draining impulse lines. 

Column AP is most commonly measured by installing a AP transmitter above the top of the column with self-draining impulse lines. Sometimes, to facilitate maintenance, it is located above the condenser or condensers, which are usually near ground level. Vapor line AP, however, may introduce considerable error. The high-side impulse line is usually connected to the vapor space just under the bottom tray, and usually enters the column at an angle to facilitate draining. 

There is no provision for continuous circulation and self draining of the pipeline or sample line (electrodes sit in stagnant process fluid). 

Numbers in brackets refer to figure 1. Consolidated drained tests will be performed in a high pressure cell (confining pressure up to 60 MPa) connected to two independent drainage lines (4 5). The first one provides a pore pressure up to 60 MPa at the top of the specimen, the second one is linked to the bottom of the specimen. Hence we can control pore pressure in an independent way at the top and at the bottom of the specimen at the same time, as to impose an hydraulic gradient. For the axial load, the cell has a vertical self-contained piston (1) which can provide a deviatoric... 

Each holdup tank is constructed on a concrete pad that drains to a dry well so that monitoring for leaks is possible. Each pair of tanks is supplied with One self-priming 50-gpm pump located above it so that leakage from the pump drains back to the tanks. The pump and tank piping is. such chat (1) the tank can be stirred. by recirculation, (2) a sample can be taken, or (3) the contents can be delivered to the retention basin, the effluent pond, dr the 10,000-gal permanent-storage tanks. The tanks in each pair have overflow lines to each other. Each tank is provided with a level gauge and a high-level alarm. 

Lines will be self-venting if the following correlation is used to determine drain nozzle sizes ... 

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