Drain points

The area below the stack and windbreaker is paved with concrete, surrounded by a 200 mm curb, and graded to a central drain point from which a drain line is routed to a manhole in a vented section of the oily water sewer. The water inlet should be sealed and the manhole should be located at least 15 m from the windbreaker. 

When possible, drain points in a pipeline should be fitted at low points, and slip-plates should be fitted at high points. 

The furnace was too near the drain point (it was about 10 m away), and the slope of the ground allowed the benzene to spread toward the... 

It was never discovered who installed this unauthorized substandard drain point. An attempt had been made to publicize the lessons of Feyzin, the company s standards, and the reasons for them. However, this did not prevent the installation of the drain point. Note that a number of people must have been involved. Besides the man who actually fitted it and his foreman, someone must have issued a work permit and accepted it back (when he should have inspected the job), and several persons must have used the drain point. Many must have passed b. If only one of them had recognized the substandard constmction and drawn it to the attention of those responsible, the fire would not have occurred [10]. 

Two drain points were choked and one isolated. In addition, the change in diameter of the main provided an opportunity for condensate to accumulate. The main should have been constructed so that the bottom was straight and so the change in diameter took place at the top. 

In this case a manual drain valve is fitted at each drain point on the steam system, bypassing the trap... 

A length of 150 mm (6 in) main carries steam at 17 bar (2501b/in ). Drain points are located at 45 meters (150 feet) intervals, with collecting legs 100 mm (4 inches) diameter x 700 mm (28 inches) long. The main is brought up to pressure from 21°C (70°F) in 30 minutes. 

It is clear that in most cases other than very large distribution mains, in TD traps are sufficiently large. With shorter distances between drain points, or smaller diameters, then i in low-capacity traps more than meet even start-up loads. On very large pipes it may be worth fitting I in traps, or two in traps in parallel. Low-pressure mains often are drained through float/thermostatic steam traps, and these traps are now available for use at much higher pressures than formerly, where it is known that waterhammer will not be present. 

In some cases, the ground contours are such that a steam main can only be run uphill. This will mean that the drain points should be closer together over the uphill section (say, 15 m (50 ft) apart) and the size of the main increased so that the steam velocity is not more than about 15m/s (50ft/s). The lower steam velocity may then allow condensate to drain in the direction opposite to the steam flow. 

Condensate from the low-pressure coil together with that from the flash vessel will then drain to a collecting tank, or direct to a condensate pump, for return to the boiler plant. If the pressure of the flash steam is left to find its own level it will often be sub-atmospheric. As the condensate must then drain by gravity through the steam traps these also must be sufficiently below the condensate drain points to provide an appropriate hydraulic head, and a vacuum breaker fitted above the coil. The alternatives are to allow the condensate to drain directly to a condensate pump, or to supply additional low-pressure steam through a pressure-reducing valve, to maintain a positive pressure in the coil and flash vessel. 

If expansion fittings are to work as intended, it is essential that the steam line is properly anchored at some point between the expansion fittings. Guiding is also important to ensure that any movement does not interfere with the designed fall towards the drain points. 

The interior of the pipelines through which the discharge air passes to the aftercooler or air receiver should be cleaned regularly so that a build-up of combustible oily carbon deposits is avoided. All the piping should slope downwards in the direction of airflow to a suitable drain point at the lowest point of the pipeline. 

Fig. 10.12 Schematic representation of a pipewall subject to cathodic protection (see text), t , = overpotential at x 7) = overpotential at x = 0 7)p,oi = overpotential at x = a/2 1, - current line at x = current density entering line at x / = current in line at x = 0 from one side of drain point (2/ = total current drain) a = distance between the drain points...

We assume that the current enters the pipeline from the soil side through defects in the coating and returns to the power source via the line and one of the drain points, as shown in Fig. 10.12. If the total current in the pipeline at a point a distance x from a drain point is /, then the change in current per unit length at x is the current entering at x ... 

However, if the pipeline has multiple drain points separated by distance V and the aim is that the pipeline electrode potential should just reach the protection potential at the mid-point (x = a/2), then is equal to (the overpotential required just to achieve the protection potential). At X = a/2 the current in the line is zero and (d nx/dx), 2 also zero. Thus ... 

In some cases a closed drainage system can be used which drains process components directly into the oily water sewer. This has the advantage of avoiding releases of vapors in any instance, but assurance must be obtained that back pressure from one drainage location will not backfeed liquids into another drain point when two valves are open simultaneously or other drainage valves can contain any backpressure on them from other drainage sources. 

The surface below pipes in a pipe trench should have a 1% slope toward one side of the trench and toward a drain point so that spills will quickly drain away from the pipes. A drainage channel 10 ft (3 m) from the edge of a pipe trench is desirable for fire protection. 

Dynamic Vacuum. Once the maximum initial vacuum has been reached, the vacuum pump is kept running while a 5-10 min. steam-injection is performed from the side of the chamber that lies opposite the vacuum drain point. Modern autoclaves can perform both methods depending on the load to be sterilized. 

Where possible, tanks and other permanently installed vessels should be connectable to drain points to collect washings and rinsings. 

Table E15.1 Potential Survey Data for the Cathodic Protection of a Steel Pipeline Parameter Drain Point 1...

Assembly drawings—nozzle orientations for gas inlet/exit/thermocouples/sam-pling points/bottom drain point Specifications of brick lining and filter mass Sample of filter mass used External insulation and cladding Quantity of dust removed dming shutdown... 

Flanged joints not provided in long pipelines. Suitable drain points and valves not provided in liquid pipes vent valves not provided in gas pipes may become difficult to clean/replace pipelines. 

Drain points and vent nozzles with valves. 

Provision of valves for steam inlet and outlet, safety, fitting of pressure gauges, vents, drain points for any condensate formed on gas side. 

Compressed air is usually distributed on a similar principle to steam, if it is required in several areas. If there is a main user, the compressor may be located adjacent to it, but it is often convenient to centralize all services in one area. As with steam, the size of the compressor and the pressure to which it raises the air will be dictated by the equipment it serves. The usual operating pressure is 100 psi and, like steam, this will be reduced where required by the use of reducing valves. The main distribution circuit may well be a ring main and it will certainly have drain points, but in this case water will be discharged from the trap, which is usually float operated. 

Carefully observe elevations of different portions of pipelines. Examine possibility of formation of idle pockets, U-seals (in sections of descending and rising pipe lengths). Provide suitable drain points with valves at appropriate locations for liquid lines. Collection tanks should be available. 

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