Shell and tube heat exchanger failure analysis (reproduced)
Read the number：(2301) Time：2014/3/9 11:20:40
Shell and tube heat exchanger failure analysis (reproduced)
Shell and tube heat exchanger is a traditional, the most widely used heat exchange equipment. Due to its rugged construction, and can choose a variety of manufacturing materials, so highly adaptive. Shell and tube heat exchangers are widely used in various industries, cement production enterprises in the oil cooler device commonly used for lubrication oil station for use as a vehicle engine oil cooler. For a long time, the steel shell and tube heat exchanger with its rugged, high reliability, and adaptability to a wide selection of advantages in the production and use of heat exchangers number has been dominant. With the enhanced development of technologies such as heat transfer, shell and tube heat exchangers and heat transfer in the manufacturing technology to continuously improve performance. However, due to the complexity and diversity of the use of structural conditions, they often appear localized heat exchanger failure or even a whole scrapped.
2 shell heat exchanger component failure modes and preventive measures
Shell and tube heat exchanger main components include: cylinder, head, tubes, tube sheets, baffles, receivership, flanges, etc., in different conditions and media environment that may occur in various forms failure. From the structural analysis, failure-prone parts of the connection between the various components, such as the connection tube and the tube plate; force from the point of view of structural discontinuities in the surface, in particular the stress due to the mutation of the additional stress often caused by the failure, such as weld tube and tube sheet; from use conditions analysis, due to high temperature and pressure caused by thermal stress or additional stress, the working medium is corrosive, causing frequent off on tubes of fluid-induced vibration, etc., can cause cylinder, tubes and even machine failure.
2.1 bundles fail
(1) bundle corrosion and abrasion failure
Most of the heat exchanger failure caused by corrosion. The most common site is the corrosion of tubes, followed by a tube sheet heat exchanger head and took a small diameter.
The main reason for the failure of corrosion and abrasion bundle are: ① dirt corrosion; ② fluid is corrosive; ③ tube wall of a foreign body accumulation localized corrosion; ④ pipe end crevice corrosion.
Preventive measures include: ① regular cleaning tubes; ② reasonable selection; ③ adding inhibitor in the fluid; ④ Set in fluid inlet filter and buffer structures.
(2) decrease in heat transfer capacity
In the heat exchanger during operation, due to the higher hardness of the working medium or fluid containing particulate matter, suspended matter, will result in tube bundle outer severe fouling. With the thickening layer of dirt, thermal resistance increases quickly, severe dirt will clog the working medium flow path, resulting in the ability to quickly lower the heat.
Prevention methods are: ① fully grasp easily contaminated site, the extent of contaminant substances and dirt, carry out regular inspections; ② When the fluid is very easy to scale, it must adopt easy to check, equipment or structure demolition and cleanup.
(3) bundle leak
In the heat exchanger corrosion, stress corrosion, crevice corrosion or collision, abrasion and other circumstances, the tube will produce microscopic cracks, or if there is a high tensile stress alternating stress, cracks will quickly expand and leak. At this point, the site used as a way to plugging the emergency restoration measures. After plugging in fact due to the increased thermal stress, thereby speeding up their stress corrosion, which will happen soon tube more serious damage, as well as causing the overall bundle scrap. Leak prevention methods should bundle selection, corrosion, damage prevention, and prevention of tensile stress decreases vibration and other considerations. Once the operation bundle leaks, replace the tube should be removed, rather than plugging.
2.2 bundle and tube plate connection failure
Depending on the heat exchanger use conditions, connectors in the form of tubes and tube plate can be divided welding, soldering Expansion and bulging with three. Connectors in different forms, failure modes are different. Using conventional methods in the welding welding products, welding overhaul can change to enhance the strength of the weld between the tubes and tube plate (see Figure 2).
① sided double-sided welding to welding; ② becomes flush welded tube plate and the front end of the tube bundle bundle extends a certain length of angle-welded construction, manufacturing special tooling will bundle and tube plate changed from flat position Vertical discharge status change form vertical weld tube to tube sheet welding the front side of the form in order to achieve the level of fillet weld welding requirements. Improve the welding process by the above two methods, you can receive good results.
2.3 cylinder failure
Shell and tube bundle which is basically the same work environment, and thus failure modes of the housing, preventive measures can refer bundle.
3 shell heat exchanger typical failure modes and preventive measures
Corrosion is the main shell and tube heat exchanger failure mode. In addition to the pH of the heat transfer medium itself outside corrosive, corrosive working media, as well as the presence of the shell or tube tensile stress, there is a gap between the tube and tube plate and so will accelerate corrosion, thereby causing the heat exchanger failure prevention The main steps are: reduced gap select corrosion resistant material, to improve the weld quality, regular cleaning fluid added inhibitor, control temperature fluctuations, reducing the flange connection.
4-line shell heat exchanger failure detection method
4.1 Scaling
After the heat exchanger operating for some time, if severe scaling the wall, the heat transfer capacity decreased, heat transfer medium outlet temperature less than the design parameters required; dirt to pipe diameter smaller; flow rate increased accordingly; increase in pressure loss. In this case, the scaling can be determined by examining the flow, pressure and temperature recording operation.
4.2 corrosion and wear
Medium heat, dirt, and other effects will cause the shell and tube heat exchangers, the outer surface corrosion and wear. Normally used for housing thickness, measured and estimated from external corrosion, thinning of the housing site.
4.3 Leak
Central pipe due to corrosion, vibration-induced rupture the pipe ends and other reasons due to corrosion, fatigue failure and other reasons make the connection tube and tube sheet leaks. By fluid sampling to check for leaks and destruction bundle.
5 Conclusion
The above analysis shows that a variety of factors shell and tube heat exchanger failure and material structure, heat transfer media, and other related conditions, sometimes the result of several factors working together. Thus, in the heat exchanger material selection, design, manufacturing, assembly and use of the various factors to be taken into account, as a preventive measure. For our users, the only positive to understand the performance of the heat exchanger, strictly online testing, Failure Analysis, rational use of preventive measures, in order to maximize the use of good heat transfer equipment to better serve production.
