Drain header connections

Connections to the closed drain header may be justified for large volume light ends pumps. 

Refinery preference may exceed these requirements. In such cases, additional 25 mm connections from equipment to the closed drain header may be installed (20 mm connections are generally considered adequate for pumps). 

Connections to equipment are typically 50 mm and 80 mm for process vessels and exchangers, according to the size of the equipment. Each connection includes an accessible block valve. Double block valves are provided if required. A check valve should be included if overpressure or other hazard could result from reverse flow during simultaneous drainage from more than one vessel. Individual connections from the equipment are made into the top of the drain header. 

Closed drain headers are normally provided for safe drainage of equipment containing severely toxic, corrosive, pollutant or high cost chemicals (e.g., phenol, sulfuric acid, monoethanolamine, sulfur dioxide, catacarb) where there is an appreciable inventory in a number of processing vessels in a plant. The header should be at least 50 mm in diameter, and should be tied into the major vessels and equipment with 25 mm minimum size connections (20 mm is considered adequate for pumps). The header may be routed to a gravity drain drum (with recovery to the process by pump or gas pressurization), or to a pumpout pump returning to the process, or in the case of sulfuric acid, to an acid blowdown drum. 

Usually, the closed liquid drain header is run as a separate line to the drum and provided with a high level cut-off valve with local manual reset. In some cases the closed drain system is segregated into a number of subheaders, as described earlier. Hydrocarbon liquids may be bypassed around the drum through a connection from the closed drain header directly to the pumpout pump suction, provided that the liquid can be routed to a safe disposal location, considering its vapor pressure and temperature. Emergency liquid pulldown connections, if provided, are routed to the blowdown drum via the closed drain header. 

FIG. 11-44 Typical construction of a tube bundle with plug headers (1) tube sheet (2) plug sheet (3) top and bottom plates (4) end plate (5) tube (6) pass partition (7) stiffener (8) plug (9) nozzle (10) side frame (11) tube spacer (12) tube-support cross member (13) tube keeper (14) vent (15) drain (16) instrument connection. (API Standard 661.)... 

Several 25 mm valved stubs should be provided at appropriate points in the header, to which temporary drain connections can be made from equipment where permanent connections would not be justified because of infrequent usage or small inventory. The stubs should be located at grade, within 30 m of such equipment. 

Steam headers should drain to the steam separator for more effective condensate collection. Branch connections to steam headers usually connect to the top to avoid excessive condensate drainage to equipment. 

Each SCB incorporates a water washdown system to periodically clean inner SCB surfaces that become contaminated. This is accomplished to maintain the working environment as clean as possible to maintain product purity. The system consists of a supply manifold located in Room 114, water supply piping inside of the Zone 2A canyon, nozzles on the top of each SCB, and a drain system that will allow injected water to drain out of the SCB into a collection tank. The system is not permanently connected to a water supply and would only be activated when ail process materials, including radioactive targets, have been removed from the SCB which is to be cleaned. To effect cleaning of the SCB, a pressurized water filled container is connected to the system each time a cleaning operation is desired. The supply of water to a specific SCB is controlled by valves in the supply header. 

The control strategy, presented in Fig. 11.35, provides smooth transfer with precise control. It must allow controlled venting as well as controlled transfer to compression, and so it requires two control valves and split-range control. The cell room header pressure is measured by a d/p cell with a Monel diaphragm. If desired, a flush-type cell can be used. It is located on top of the header as it leaves the cell room. It is important that connections to the d/p cell be freely draining. 

In the air distribution system, all takeoffs should be from the top of the pipe or header. Headers should slope towards their ends and should include terminal drain/blowdown valves. Connection points for hoses should be standardized throughout each plant and should carry prominent reminders to blow out the line before use. 

Header boxes, as shown in Exhibit 7-19, are enclosures around the fittings that connea two tubes. The fittings, called headers, are furnished with plugged connections for cleaning. The header boxes are sealed from the inside of the furnace by an insulated tube sheet, and, because this area is a possible source of fire, a snuffing steam connection is provided for fire suppression. A drain conneaion is so provided for leak deteaion. Clear access must be provided around the header box to permit inspeaion and tube cleaning or replacement. 

Vent and drain connections are usually provided at top and bottom of header box. Pressure or temperature mstniment connections are usually provided at irdet and outlet nozzles. 

The PANDA-PCC consists of 20 vertically arranged tubes connected at their ends with drum-type headers. The upper header has a connection for steam supply, the bottom header has a drain for the condensate produced and a drain for non-condensable gases. The tubes of the PCC have an outside diameter of 50.8 mm and a wall thickness of 1.65 mm. They are made of austenitic steel. 

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