Why wasn’t a corrosion allowance considered for the heat exchange tubes?
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In heat exchange equipment, corrosion allowances are taken into account for all pressure-bearing components. Only non-compressed originals do not take corrosion allowance into account. But the heat exchange tubes are an exception. In my opinion, first of all, the heat exchange tubes are subjected to very little stress... They can be considered as non-compressed components... I hope those with experience can share their insights
GB151 explicitly states that no corrosion allowance is considered for heat exchange tubes. Heat exchange tubes do have some margin for corrosion resistance, but their primary function is to improve heat transfer efficiency. In situations where there is corrosive media present, it is possible to upgrade the grade of these tubes; for example, carbon steel equipment can use stainless steel heat exchange tubes ； Increasing the wall thickness is not recommended, as a greater wall thickness leads to a significant decrease in heat transfer efficiency; it’s like gaining something small at the expense of losing something much more valuable. It is not suitable from both economic and practical perspectives
I agree with what was said above; the heat exchange tubes are the core components of a heat exchanger. Whenever possible, under conditions that permit it, it is advisable to use tubes with a small diameter, thin walls, and a smooth surface as heat exchange tubes. We currently use mirror-polished tubes
This post was last edited by jia717 on 2009-9-1 at 12:34. It’s not the case that heat exchange tubes are ignored just because they are subject to less stress; the thickness of these tubes determines the efficiency of heat exchange. When exposed to corrosive substances, materials resistant to corrosion must be used for making the heat exchange tubes. Actually, this principle is easy to understand: if corrosion margins are applied to the heat exchange tubes in the same way as they are for pressure-bearing components, the tubes will become very thick, heat transfer efficiency will drop sharply, the heat exchange area will **increase**, and the size of the equipment will become enormous.
You can search for information on the corrosion margin of heat exchange tubes; there are many relevant discussions available. You can take a look at: http://bbs.hcbbs.com/viewthread.php?tid=270419&page=1&extra= http://bbs.hcbbs.com/viewthread.php?tid=443940&highlight=%BB%BB%C8%C8%B9%DC%2B%B8%AF%CA%B4
I took a look at the post posted upstairs. I think their discussions didn’t yield any definite answers either. I asked another professor today, and to sum it up: 1. Heat exchange tubes are primarily used for heat transfer; taking corrosion allowance into account, too thick tube walls are not conducive to heat transfer. 2. The corrosion of pipes was taken into account during the initial design phase, with efforts made to minimize such corrosion, primarily through the selection of appropriate pipe materials. 3. Pipes have a high pressure resistance capacity; for example, with a pressure difference of 10 M and at a temperature of 200 degrees Celsius, a pipe with an outer diameter of 19 requires only a wall thickness of 0.5 mm. Typically, the wall thickness is around 2–3 mm, so there is some margin of safety. Moreover, the corrosion allowance specified for the materials used in equipment, such as 3 mm for carbon steel, is quite conservative. Considering the service life of the equipment and taking into account the rate of corrosion, such a large thickness isn’t actually necessary. 4. The pipes are damaged; some of them can be replaced. But the economic losses caused by overly thick pipes are significant... That’s basically all. I hope everyone will point out any mistakes, and I welcome any other opinions for discussion
Well, if the thickness is too large, it will affect heat transfer. If the tubes are damaged, they can be replaced. However, in a shell-and-tube reactor the tubes are inside and not visible; so how can one detect damage to the tubes?
Primarily, the wall thickness has a significant impact on heat transfer efficiency; taking corrosion margin into account further makes it uneconomical.
From what I’ve seen in previous discussions, the key points were more or less covered; one needs to evaluate for themselves to find the exact answer
Gas contains a large amount of chloride ions, which cause severe corrosion of stainless steel; this factor must be taken into account. The leak in our heat pipe exchangers was caused by corrosion resulting from the gas.
Agree with the opinion about two pieces of ice. However, I have reservations regarding the use of mirror tubes as mentioned by you*. The higher the surface smoothness of the tube wall, the more likely it is that a layer of liquid film will form on its surface, which hinders heat transfer. Of course, a higher surface finish makes it less prone to scaling and easier to clean. My opinion is that for general-purpose heat exchangers, ordinary tubes should be used for the heat exchange tubes, as heat exchange efficiency is the most important factor. In industries with hygiene requirements such as food and pharmaceuticals, smooth tubes are used for heat exchange tubes, as they are easy to sterilize and clean, and do not cause cross-contamination of products. I hope everyone shares their opinions!