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| Sulphuric Acid on the WebTM | Technology Manual | DKL Engineering, Inc. |
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Knowledge for
the Sulphuric Acid Industry Introduction
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Piping is used to convey fluid from one location or vessel to another location. Without piping there would be no process. The importance of piping is equal to that of any piece of equipment. Liquid must be conveyed safely, efficiently and economically from one point to another. Materials used for acid piping have evolved with the design of acid plants over the years and with the introduction of new materials. The two most common materials used for the main acid circulating lines are cast/ductile iron and alloy materials. The main differences, advantages and disadvantages are listed in the following table.
Acceptable velocities in acid piping will depend on a number of different factors such as:
The following are general guidelines for maximum design velocities in various pipe materials.
The weak point in any piping system are the connections between spool pieces, in-line instruments, valves, and equipment. When the fluid being carried is not dangerous, leaks at these connections is not a critical safety issue, however, when the fluid is hot concentrated sulphuric acid, safety becomes a major concern. In acid piping systems all connections should be flanged connections. Screwed connections are not recommended under any circumstance. Leak may occur at the flange connections due to corrosion, wearing out of the gasket, poor or inproper installation. If the system operated under high pressure, leaks may result in acid spraying out into the operating area. This hazard can be mitigated by the use of flange guards. Flange guards is a safety shield that complete encloses the flange preventing the sprayout of acid. The spray is contained and is converted into a drip which is less hazardous. There are two opinions as to whether or not sulphuric acid lines should be flushed with water and/or subjected to hydrotesting during construction. The concern is that if water remains in the lines when sulphuric acid is introduced, there may be a violent reaction due to the sudden mixing of water and acid. As well, the formation of weak acid in the system may lead to increased corrosion and eventual leaks. Alloy piping system are more easily damaged by weak acid than ductile iron systems. The case for flushing and hydrotesting acid lines is that leaks can be detected before acid is introduced thereby reducing hazards during the initial filling and circulation of acid in the lines. This is of particular advantage for ductile iron piping systems which have flanges at each fitting and spool piece. For alloy piping systems the number of flanges is greatly reduced so the need to hydrotest the system is less. Flushing and hydrotesting can be done safely provided certain precautions are taken. The first step is done during the design phase when the piping is laid out. Low points and pockets should be avoided and if they are present, a drain should be provided. After flushing and hydrotesting the lines, all water must be drained from the system and the line purged with air until all moisture has been removed.
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Copyright© 2005,
2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
