Why is it necessary to consider a corrosion allowance for the skirt seat?
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Requirement 20580 specifies that the minimum corrosion allowance for the skirt cylinder shell should be 2 mm. Generally, the skirt base is painted, right? So why is it necessary to consider a corrosion allowance?
The skirt is the main load-bearing component, affecting the safe operation of the tower; painting it does not ensure protection against corrosion by the atmospheric environment over the long term.
There’s some truth to it. That support serves a function similar to that of a skirt, so why is it not necessary to take corrosion allowance into account?
2mm is the corrosion margin inside the skirt. Because the interior of the skirt seat is generally not painted. It’s difficult to perform proper surface treatment on the interior, especially at the angles and gaps where it comes into contact with the main body; as a result, even if paint is applied, it peels off after a short time. So it’s better not to carry out any treatment or apply paint at all. If the diameter is large and the material is expensive, surface treatment followed by painting can be used, eliminating the need for a corrosion margin.
In my opinion, equipment that is supported by brackets is generally smaller in size and weight compared to towers, and it holds a lower role in the overall chemical production process; therefore, no specific requirements regarding corrosion margin for its support structure are specified. However, designers can decide on an appropriate value for the corrosion margin on their own
One more thing: the skirt seat is exposed to certain levels of temperature, which accelerates corrosion.
By the way, I’d like to ask: do the load capacities and size specifications recommended in the standard for \"Container Supports\" take into account a corrosion margin? Is the corrosion allowance uniformly reduced according to atmospheric conditions, or is anti-corrosion treatment applied in all cases, which is why corrosion is not taken into account?
I guess no one will answer questions here. I used SW6 to simply calculate the cross-sectional area of the saddle (which is used to determine the compressive stress on the saddle and thus its load-bearing capacity). The formula used included the given thickness without deducting for corrosion allowance; therefore, it’s reasonable to assume that the standards also do not take corrosion allowance into account. .
NB/T 47041-2014 \"Tower-Type Containers\" 4.2.5.2d) stipulates that for skirt shells made of carbon steel or low-alloy steel, the corrosion margin shall be not less than 2 mm； ...... It is in accordance with the requirements of HG/T20580 \"Basic Provisions for the Design of Steel Chemical Containers\".
The skirt base definitely requires a corrosion allowance, whether or not anti-corrosion measures are taken； Also, please do not forget that when designing the tower, the anchor bolts should also be given the same corrosion allowance as the equipment; this is something that some people overlook