Analysis of the causes of air preheater tube bundle leakage
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This post was last edited by chuan21206 on 2022-9-27 at 10:59. I. Basic Overview: Our plant’s air preheater was manufactured and installed in 2020; it uses medium-pressure saturated steam to preheat the compressed air entering the CLAUS furnace to 230°C. During the major maintenance in September 2022, a pressure test conducted according to the design parameters for the shell side revealed leaks in the 1st/3rd tube banks. The other two heat exchangers with similar operating conditions have been in use for 6 years without any leaks, and I would like to ask experts for help in analyzing the reasons. The parameters of the heat exchanger are shown in the table below: II. Preliminary cause analysis 1. Corrosion factors: The media in the tube side and shell side are steam/compressed air respectively, so the possibility of corrosion is low. At the same time, since the medium is not highly corrosive, it is also acceptable to use Q245R (for the shell side) / 20# (for the tube bundle). 2. Operational factors: By examining the historical trend of steam consumption, it was found that after the operation of this heat exchanger, the maximum steam consumption was approximately 2.8 t/h. The designed steam flow rate is 3.85 t/h; the actual steam flow rate is lower than this designed value, so there is no risk of tube bundle damage due to excessive steam flow. 3. Comparison of relevant heat exchangers: Compared with the primary and secondary reheaters, the main difference lies in the temperature of the fluid flowing in the shell side. The inlet temperature of the fluid in the shell side of the air preheater is 60 degrees Celsius, while the lowest inlet temperature for the fluids in the shell sides of the primary and secondary reheaters is 187 degrees Celsius. However, the maximum temperature difference between the fluid on the tube side and that on the shell side in the air preheater is 193 degrees Celsius. Whether such a large temperature difference could lead to leaks requires further analysis and discussion with relevant experts. 4. Manufacturing quality factors: Spectral analysis results show that the material and design of the tube sheet and tube bundle are consistent, ruling out material-related issues. Therefore: the quality of the heat exchange tubes purchased, or mechanical damage during installation, are possible factors that caused the leakage in this tube bundle
Problems existing: 1. Objective factors: Corrosion occurs. 2. Material issues: 20# steel is used in the tube bundle design, with a design lifespan of 3 years. 3. Operational factors: When the actual steam flow rate is lower than the designed value while the air volume remains unchanged, it inevitably leads to more condensation of steam during the heating process than intended; liquid slugging becomes unavoidable, and erosion occurs as a result.
This post was last edited by chuan21206 on 2022-9-19 at 13:33. One more question regarding point 2: 2. Material issue: 20# steel is used for the tube bundle design, with a design lifespan of 3 years. What is the typical design service life of other commonly used carbon steel pipes? Such as 10# steel...... etc
This post was last edited by chuan21206 on 2022-9-19 at 13:33. Thank you very much. I have another question regarding point 2: 2. Material issues: 20# steel is used in the tube bundle design, with a design lifespan of 3 years. What is the typical design service life of other commonly used carbon steel pipes? Such as 10# steel...... etc
Very professional; thanks for sharing, I’ve learned something!
There are no reports to date on how long the design service life of commonly used carbon steel pipes is, as it depends on the operating environment.
A large temperature difference is most likely the cause of this issue. Check the temperature of the condensate; it’s possible that water hammer has occurred inside the pipes. It is recommended to use a two-stage air preheater: in the first stage, low-pressure steam is used to raise the air temperature to over 100 degrees, and then medium-pressure steam is used to heat the air to the designed temperature
Thank you for your suggestion; I’ll go check the hydrophobic temperature later to make a comparison.