Tube leak heat exchanger

Equipment Failure pumps, tubes in heat exchangers and furnaces, turbine drivers and governor, compressor cylinder valves are examples of equipment which might fail and cause overpressure in the process. If an exchanger tube splits or develops a leak, high pressure fluid will enter the low side, overpressuring either the shell or the channels and associated system as the case may be. 

Tube leaks may occur in the reboiler, condenser, preheater, precooler, or any other heat exchanger linked with the column. Several experiences where leakage caused poor performance have been reported (71, 238, 239). The effect of a leaking heat exchanger tube depends on the magnitude, the direction, and the location of the leak. 

The point of this story is that the integrity of any piece of process equipment should never be taken for granted. The tubes in heat exchangers are prone to leak. This point is emphasized by the following incident. 

GHXTLK Glycol heat exchanger tube leak... 

Failure of Heat Exchanger Tubes If a heat exchanger shell rating is less than the pressure level of the circulating medium and an internal heat exchanging tube ruptures or leaks it will overpressure the vessel. 

Heat exchangers that can be blocked in or where the shell of the exchanger may be subject to high pressure if an internal tube leak occurs. 

The reason illustrates the true nature of the shell-and-tube heat exchanger. It is a compromise between an ideal heat-transfer configuration and practical mechanical limitations. In this case, the difficulty is preventing leakage around the longitudinal baffle. Such leaks permit the shell-side fluid to short-circuit the tube bundle that is, a percentage of the inlet flow, may flow directly to the outlet nozzle. In extremely serious cases, I have seen the bell head (shown in Fig. 19.8) 100°F colder than the shell-side outlet temperature. 

Testing for structural integrity and testing for tiny leaks sometimes require two different approaches. Sometimes it is necessary to find leaks in systems such as a heat exchanger, which has hundreds of tubes rolled into a tube sheet. Water drips from a hydrotest may be hard to see or correct. At other times you may need to test gasketed systems that will not tolerate moisture. 

Air-cooled condensers are especially attractive at locations where water is scarce or expensive to treat. Even when water is plentiful, air coolers are frequently the more economical alternative. Elimination of the problems associated with the water side of water-cooled equipment, such as fouling, stress-corrosion cracking, and water leaks into the process, is an important advantage of air-cooled equipment. In many cases, carbon steel tubes can be employed in air-cooled condensers when more expensive alloy tubes would otherwise have been necessary. The use of air-cooled heat exchangers may eliminate the need for additional investment in plant cooling water facilities. 

The second method provides a double barrier within the steam generator itself. The double barrier has conventionally been in the form of concentric tubes and double tube sheets with the intermediate space filled with a static third fiuid to assist in the transfer of heat. The third-fluid system was equipped to detect any leaks which might occur in either of the single barriers. Under the doublewall philosophy as originally developed, if a leak occurred in either barrier, the heat exchanger was taken out of service for repair or replacement. 

Effects of heat exchanger tube leaks into the column include off-spec products and/or undesirable chemical reactions. In some cases, this reaction may lead to rapid corrosion or plugging. It is important to realize that material leaking at the condenser or at an intermediate exchanger may travel to the column base and decompose there. In one vacuum column, water leaking at the condenser reached the reboiler and caused a pressure surge and tray damage (358). 

Effects of heat exchanger tube leaks out of the column include inability to maintain column pressiure, erratic performance of reboiler or condenser, and erratic performance in other units because of contamination of the heat transfer medium. One classic experience (239) of an extremely sick column performance caused by a leaking reboiler was described in Sec. 1.2. 

The commissioning and operation of sodium systems and components have been smooth and performance of major components, viz., sodium pumps, intermediate heat exchangers and once through sodium heated steam generators (SG) have been excellent. There have been three minor incidents of Na/NaK leaks during the past 14 years, which are described in the paper. There have been no incident of a tube leak in SG. However, three incidents of water leaks from water / steam headers have been detailed. 

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