Material selection issues for 45bar steam
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One reboiler, with 45 bar steam as the fluid in the tube side; the U-shaped heat exchange tubes are made of 316L, while the tube sheet is made of Q345R (the flanges are forged from 316L). The shell material is Q345R (the shell flange is 316L forgery). My question is: Why isn’t carbon steel used for U-shaped heat exchange tubes? Is it due to issues related to the processing of U-shaped tubes? Thank you. For the device structure, please refer to the diagram below:
Today I encountered a vertical heat exchanger of a similar type: steam at 45 bar in the shell side, while the fluid is on the tube side. The material used for the shell and the upper and lower tube boxes is Q345R; only the tubes are made of 316L. I’m confused – could it be that this project has an extremely large budget? :D
In this case, it is generally because the material has a certain corrosive effect on carbon steel; the casing is made of carbon steel as corrosion allowance was taken into account during the design process. Given the thin wall thickness of the heat exchange tubes, and without taking into account a corrosion allowance, stainless steel is used for these tubes to ensure they meet the requirements for their designed service life.
This explanation is reasonable, but given the ways in which steam is used in our plant, carbon steel pipes can operate for up to 12 years without showing any significant corrosion. If Cl ions in the steam are not properly controlled, especially at the vapor-liquid interface of the condenser, stainless steel is much more dangerous than carbon steel. There was once a case found of stress corrosion cracking in austenitic stainless steel tubes at the steam-liquid interface of a heat exchanger.
I think the explanation for the second floor is reasonable, but this approach is not economical~~~ Premise: The medium does not cause corrosion to carbon steel at high temperatures~~~ If 15CrMoG (GB5310) is used for the heat exchange tubes, it fits my preferences better :)~~~ Using stainless steel results in a thermal conductivity that is much lower than that of carbon steel or low-alloy steel~~~ This requires a much larger calculation area for the heat exchanger, which in turn increases the risk of leaks~~~~
What is the temperature of steam at 45 bar? What is the operating temperature for carbon steel?
This post was last edited by xlxuiin on 2017-11-2 at 16:28. Additionally, it applies to situations where the pressure of the fluid in the tube side is high, or where the fluids on the tube side and shell side must not mix with each other. Upgrade the material selection and configuration of the tube bundle to improve reliability. (Here, cost-effectiveness is of secondary importance.)
Completing the parameters will allow us to analyze it for you more clearly. Media, temperature, pressure, etc. of the shell and tube sides
In my opinion, the main consideration is corrosion; when there is corrosion on both sides of the heat exchange tubes, using carbon steel results in the tube bundles being damaged very quickly. Increasing the wall thickness of the heat exchange tubes would affect the heat exchange efficiency, so from a technical perspective, stainless steel is the only viable option