Hazards continued piping

In de-aerated conditions, for instance in most central heating systems, little if any attack on copper occurs . As far as drinking waters are concerned, copper is not classified as a toxic substance or hazardous to health. To avoid any difficulties due to unpalatability, the maximum continuous copper content should not exceed 10 p.p.m., with a limit of 3 p.p.m. in water after standing overnight in copper pipes. A review of the subject by Grunau makes reference to 394 published papers. 

The chemical reactor is the most hazardous unit in any chemical plant because most accidents occur by uncontrolled reaction, either within the reactor or after reactants have escaped the reactor and perhaps reacted with oxygen in air. Obviously no reactor or piping can withstand the temperatures and pressures of total combustion unless designed specifically for these conditions. We will consider the energy balance and temperature variations in continuous reactors in more detail in Chapters 5 and 6, while flames and explosions will be considered in Chapter 10. 

A variation of the dry-pipe system is the deluge system. The sprinkler heads are continuously open and water is prevented from entering the system by a deluge valve. When a fire is detected the valve to the water supply opens and water flows into the system and out of aU the sprinkler heads. This not only wets the immediate area of a small fire, but the entire area to which the fire may spread. This type of system is usually chosen when the contents of the space are unusually hazardous. A variation on this system is the pre-action system in which the sprinkler heads are not open, but when a fire is detected the deluge valve opens and water is supplied to the sprinkler heads. The water entering the system causes an alarm to be sounded. When the heat causes the sprinkler heads to fuse, or open, water is discharged onto the fire. 

Water presents the hazard of rapid corrosion organics by reaction with chlorine can produce local hot spots and ultimately cause temperatures above the allowable maximum (Section 9.1.2), which in the case of carbon steel is usually set at 120 C. Oxide layers on the surfaces of equipment, pipes, or fittings increase the amount of water absorbed. This is an exothermic process. The increase in temperature not only increases the rate of corrosion but also can continue beyond the ignition limit. 

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