I would like to ask: some clients require that the cylinder body of pressure vessels be made of 304 or 304L material, while the head should be made of 316L material
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I would like to ask: why do some clients require that the cylinder body of pressure vessels be made of 304 or 304L material, while the head is made of 316L material? What are the reasons behind this?
The main consideration in using different materials is to address the varying corrosion conditions of the medium inside the container and the working environment. 304/304L materials possess good general corrosion resistance and a relatively low cost, making them suitable for use in cylinders. Material 316L contains higher levels of nickel and molybdenum compared to 304/304L, which provides improved corrosion resistance, especially against chlorides. It is therefore suitable for use in the head sections of containers, as these areas are often the most susceptible to corrosion within a container. By using such a combination of materials, both the corrosion resistance of the entire pressure vessel is ensured and costs can be controlled. .
It’s obviously unreasonable; it seems that those who make the decisions don’t understand technology, while those who do understand technology aren’t able to make such decisions.
Guess: It should be a vertical container with liquid accumulated at its bottom; the corrosivity of this liquid is greater than that of the gas phase, which is why a more corrosion-resistant material is used for the head.
What was said on the 3rd floor makes sense; I’ve encountered that too
Previous projects also had this requirement, which was put forward by the equipment specialists; this was because cracks had occurred in the heads of storage tanks made of 304 material. For subsequent projects, given the special requirements related to 304 material storage tanks, it became necessary to use 316L material for the tank heads. Here, by \"head\" is meant a head manufactured using the spinning process； If the entire material of the storage tank is 316L, then this problem does not arise ；
This is because the end caps undergo significant deformation during processing. For stainless steel end caps such as S30408, S30403, and S32168, which have a lower dislocation energy, deformation-induced martensitic transformation occurs more easily during plastic forming compared to stainless steel end caps like S31608 and S31603, which have a higher dislocation energy. As a result, more severe corrosion occurs in these end caps over time. This phenomenon has been observed in many installations; therefore, some owners request that end caps be made of 316L material in order to avoid such risks.
In that case, it is the situation described on the 7th floor: after compression, the corrosion resistance of the end cap decreases. In fact, at this point, solution treatment after the end cap has been formed should be employed, which can restore a large extent of its corrosion resistance. However, the cost of solution treatment is not low; if the diameter is small, it is actually more economical to use 316L material instead.
I agree. I guess another reason is the need for a corrosion allowance; the wall thickness of the stamped head can be specified in parentheses on the drawings, especially around the section where it transitions into a straight tube. However, this might result in insufficient corrosion allowance. Using 316L material would likely provide enough corrosion allowance……