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| Sulphuric Acid on the WebTM | Technical Manual | DKL Engineering, Inc. |
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Contents
Contact Section -
Gas-to-Gas Heat Exchangers - Fabrication
February 25, 2011
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Introduction Field Installing Tubes Roller Expanding of Tubes |
Associated Links |
It is desirable to fabricate the entire gas-to-gas heat exchanger in a fabrication shop where the fabrication process can be closely controlled and monitored. The completed exchanger is then shipped as a completed unit for erection on site. In some cases the exchanger is so large that it cannot be shipped in one piece. In this case nozzles, vestibules and bustles can be left off and installed in the field. It is still desirable to completely fabricate the tube bundle complete with shell if possible since this allows the tube-to-tubesheet joint to be done in the shop.
In some cases the size or weight of the exchanger will require the unit to be field fabricated. Field fabrication is more time consuming and costly as well as being more difficult to control the quality of the fabrication.
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Installation of tubes in the field can be done with the exchanger in the vertical position. This may be necessary if the total weight of the exchanger exceeds the maximum lifting capacity of the available crane. The top head or vestibule is left off to provide access to the top tubesheet for inserting the tubes down through the exchanger. A custom tube lifting platform is used to lift a large number of tubes up by crane to facilitate fast installation of the tubes. |
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| A custom tube lifting platform was created to lift up to 132 tubes at a time. The tubes are held in place with a bolt tightened against the tube. A worker is required on top of the platform to release the each tube while workers below guide the tube into the tubesheet hole and down through each baffle to the lower tubesheet. | |
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Roller expanding of tubes into the tubesheet is a common method for securing the tubes to the tubesheet. For gas/gas exchangers, grooving of the tubesheet is generally not required. The exchanger is generally in the horizontal position so workers are working against the vertical face of the tubesheet. |
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The roller expander is inserted
into the tube. Care is required to ensure that the roller expander does
not extend past the back side of the tubesheet. Only the portion of tube
that is in contact with the tubesheet is expanded. The portion of tube
beyond the tubesheet is should not be expanded. A heavy duty electric drill is used to drive the roller expander. |
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A torque wrench is used to verify the torque used to expand the tubes. This ensure that the joint is sound and will not leak. |
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The tubes must be positioned correctly in the tubesheet before expanding the tube. The tube is positioned by hand using a vice-grip to ensure that the tube projects from the tubesheet the required distance. |
