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A tube plug is a mechanical device used to seal off individual tubes in boiler and heat exchanger tube bundles. This process usually becomes necessary when a tube begins to leak and requires isolation from the flow of water or gas through the bundle. The plug is generally inserted into the offending pipe at the entry tube sheet to block off fluid flow into it either on a temporary basis or as a permanent measure. There are numerous types of tube plugs on the market which are usually available as low and high pressure types. Most function on an expansion seal basis and are either set up by turning an integral bolt or by hammering the plug into the pipe opening in the case of tapered varieties.
Tube bundle heat exchangers and boilers utilize densely packed groups of metal tubes which carry hot gases or fluids through an outer shell. To carry out any maintenance on the tube bundle, the entire unit needs to be disassembled and the bundle removed from the shell. Replacing a single leaking tube deep within the bundle can be a monumental task, and one that is, fortunately, not always necessary. If the faulty tube can be identified, it can simply be blocked off so that it is isolated from the fluid flow. The loss of a single or even a couple of tubes seldom has a significant effect on the bundle's efficiency, and this is where the humble tube plug can save thousands of dollars and many hours of work and downtime.
Tube plugs are small, cylindrical devices which expand to form an effective seal in high pressure pipes. In terms of design and operation, they fall into two broad categories. The first are straight walled plugs which expand to grip the walls of the tube securely to effect a seal. The second type are tapered plugs which are typically hammered into place in the mouth of the tube. Some tube plug designs are even designed to be welded into place to form a permanent seal.
Expanding tube plug designs usually consist of a central arbor which is pulled back into the body of the plug by tensioning a bolt. This expands the body to lock the plug in place. Low pressure varieties often consist of a flexible body which is extended with a special tool for insertion into the tube. This effectively reduces the diameter of the plug and allows it to slip into the tube. When the tool is removed, the plug body returns to its original diameter and locks into the tube. Expanding and hammer-in plug types are fairly easy to remove should the tube be returned to service after repairs.