#TEMA EXCHANGER TYPES FULL#
This eliminates the bolt circle diameter and allows a full complement of tubes to fill the shell. Here the floating head Bonnet is bolted to a split backing ring instead of the tube sheet. Some designs include sealing strips installed in the shell to help block the bypass steam.Īnother floating head design that partially addresses the above Disadvantages is a "split-ring floating head". In addition, the missing tubes result in larger annular spaces and can contribute to reduced flow across the effective tube surface, resulting in reduced thermal performance. In order to accomodate the rear head bolt circle, tubes must be removed resulting in a less efficient use of shell size. The simplest is a "pull-through" design which allows the tube bundle to be pulled entirely through the shell for service or replacement. In an effort to reduce thermal stresses and provide a means to remove the tube bundle for cleaning, several floating rear head designs have been established.
In large diameter shells, the long length of unsupported tube in the u-bends of outer tubes can lead to vibration induced damage. Erosion damage is also frequently seen in the u-bends in high tube side velocity applications. Also, the tube interior cannot be effectively cleaned in the u-bends. Individual tubes can be difficult of expensive to replace, especially for interior tubes. U-tube designs while offering the best answer for differential thermal expansion, have some drawbacks.
The floating head is typically sealed against the interior of the shell by means of packing or O-ring designs. An expansion joint can also be installed in the tube side of floating head designs, but manufacturing costs are much higher.Īlternative approaches involve the design of a U-tube bundle so that each tube can inpendently expand and contract as needed or by using a rear floating internal tube sheet design which allows the entire bundle as a unit to expand and contract. This is a cost effective approach for pipe-size shells. One approach in common use is installing an expansion joint in the shell pipe of such designs. When the terminal temperature difference between the fluids is substantial, over 50-60 degrees, these stresses can become severe, causing shells to become deformed and damage mounting supports, tubes to deform the tube sheet or tubes to become broken or dislodged from the tube sheet.įixed tube sheet designs are most vulnerable to differential thermal expansion, because there is no inherent provision to absorb the stresses. Since the duty of Heat Exchangers includes the handling of fluids of differing temperature, flow rate and thermal properties, differential expansion of the metals will take place. The steam will cause the tubes to expand and pull out of the Tube Sheet causing failure at startup. You should avoid using Steam cleaning on a fixed tube sheet unit unless the unit has a shell side expansion joint. Chemical, mechanical, and water blast cleaning of the tubes is possible, however you do not have access to the shell. These units are favored in very high pressure designs as their construction minimizes the tubesheet thickness and number of high pressure retaining flanges.ĪEM/BEM/AEL-Shell side is completely welded up, however, the Bonnets are removable. Access to the tubes is through covers on the channels. NEN- Tubesheets are welded to both the Shell and Bonnets. These units are commonly used in high pressure services (such as feedwater heaters), where process conditions allow for even pass exchangers. Tubes may be chemically cleaned, water blasted or steam cleaned from inside only. The tubesheet is welded to both the shell and Bonnet. NEU- The most cost effective design available. Another advantage is that they are generally more cost effective than removable bundle designs. These types of units are often used in high pressure services and services where you wish to avoid leakage problems at gasketed joints.