When should a transition section be installed at the skirt base? (The standards are contradictory)
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The standards set by the Ministry of Chemical Industry specify a design temperature of over 250, while those established by the petrochemical industry require a temperature of over 350. There’s evidence to back this up: did the people who formulated these standards decide these values arbitrarily, without any distinction between 250 and 350? Also, I don’t understand what use this transition section serves? It’s understandable to use stainless steel for the head and carbon steel for the skirt, with a stainless steel transition section added to reduce corrosion of the head. But what’s the point of adding such a transition section just because of high temperatures? Can adding an extra circumferential weld really reduce the temperature?
The skirt cylinder is a stress-bearing component, usually made of Q235 material. However, since the skirt is a very important part of the tower, it is essential to decide whether to include transition sections in the skirt cylinder, taking into account factors such as the material of the tower and the operating temperature.
I just don’t understand why a transition section is added when the design temperature is high
When the design temperature is high, materials to be used for the tower structure must include chromium-molybdenum steel, stainless steel, and similar materials. If the skirt is made of 235 or 345 grade materials, its performance at high temperatures will not be sufficient; therefore, a transition section is necessary.
Then a setting greater than 350° should be correct
1. NB/T47041 6.2.2 When the lower head of the tower shell and the skirt shell are made of different metal materials, a transition section shall be provided at the skirt. There is no requirement to provide a transition section at high or low temperatures. 2. The standard definition for applications requiring high or low temperatures is given in NB/T 47041. 3. Indeed, it’s not clear what the purpose of having a transition section at high or low temperatures is. Additionally, if 304 is used for the tower shell head, and given that the tower diameter is small as well as the height of the skirt cylinder being low, if Q235 is used for the skirt cylinder, it would be troublesome to have to include a transition section due to the difference in materials; therefore, I simply use 304 for the entire skirt cylinder ； Originally, the skirt cylinder and the head were made of the same material; if the operating temperature is greater than 350 degrees, then according to the specifications, should a transition section not also be provided? So there must be a problem with the requirements for interpretation. I hope an expert will come out and clarify this!
The transition section of the skirt base is a section with complex stress conditions; just as in the section from the building foundation up to 1 meter, it is necessary to increase the amount of reinforcement, both for shear resistance and bending resistance, among other reasons.
Tower-type equipment is indeed quite complex during the design process.
I’m still following the post from three years ago: lol. A gas barrier should be installed; temperatures above 400° mean that the transition zone is useless
Firstly, the standards for drawing design determine the requirements that must be followed, and these standards vary across different industries； Secondly, if there are discrepancies among the standards that need to be followed, the more stringent standard can be adopted ； Additionally, if there are clear conflicts between the standards that need to be followed, it is then necessary to look for amendment orders or other solutions adopted by peers. Since standards are standards, they are generally reasonable most of the time; however, there are inevitably some oversights or issues that did not arise during previous production processes