Heat exchangers are used by many industries, especially in oil refineries and chemical plants. Their purpose is to exchange heat from one place to another, usually from one liquid to another liquid. The continued efficiency of this device demands regular heat exchanger inspection to determine whether or not the integrity of the equipment.Where are Heat Exchangers Found?
Most homes also have a heat exchanger of some kind. The most common household heat exchanger can be found in a refrigerator. In hot countries air conditioners are common; another kind of heat exchanger. Cars contain them too - the radiator removes the excess heat from the radiator fluid by making use of the natural airflow caused by the car's forward progress.
A similar principle applies in large industry where heat needs to be transferred from one place to another. The most common type of heat exchanger found in oil refineries and other large plants is the "shell and tube heat exchanger".
This design employs a large shell, usually a very large diameter tube that can withstand high pressures. It contains a bundle of tubes inside. The heat exchanged is from two different fluids. One fluid flows through the shell of the exchanger while the other flows through the tube bundle. The two fluids do not make direct contact with each other, but the difference in their respective heat values is changed through the indirect contact that is made.
A shell and tube heat exchanger is a complex design. The internal tubes are often of differing types and design in order to achieve different results. Some tubes may be plain while others may be finned horizontally or longitudinally. The tubes may also be composed of different materials and different thermal conductivity. They may be made from stainless steel, carbon steel, brass, copper or cupronickel, for example.
Because of their complex nature it is necessary to have a regular the equipment regularly inspected. This can determine the wall thickness of the tubes, which are subject to pitting and corrosion as well as erosion over time. The condition of the entire tube bundle can be charted and evaluated through a highly detailed inspection using a device called an Internal Rotary Inspection System.
The Internal Rotary Inspection System works through ultrasonic testing and it is non-destructive in nature. The Internal Rotary Inspection System probe has to be inserted into a tube which is then filled with water.
The Internal Rotary Inspection System probe has a small mirror that rotates and focuses an ultrasonic beam onto the wall of the tube. The mirror rotation is driven by a small turbine, which in turn is driven by water pressure as it is pumped into the tube. The Internal Rotary Inspection System probe is slowly pulled out of the tube at a rate of about one inch or 25 millimetres per second, recording the condition of the internal wall of the tube as it progresses.
The results gained from a heat exchanger inspection using an Internal Rotary Inspection System probe is generally extremely accurate. Its accuracy can be as good as to within .005 inches, or .13 millimetres. Of course, in order to gain this level of accuracy it is necessary for the heat exchanger tubes to be thoroughly cleaned down to bare metal prior to the inspection.
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C. J. Rose writes on the subject of tube bundle and heat exchanger cleaning and onshore/offshore environmental safety for Sureclean, global industrial waste management experts. Topics include HP & UHP water jetting, tank/vessel cleaning, vacuum transfer/pumping, industrial painting, asbestos management/removal, HVAC/duct management, NORM management. For videos see http://www.sureclean.com/video.
