Regarding the issue of corrosion allowance for carbon steel
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Hello everyone, I have a question regarding the design of pressure vessels: For deoxygenated air, can a corrosion allowance of 0 be used? The material used is Q345R.
The medium contained within this pressure vessel is deoxygenated air, right? The main components of deoxygenated air are nitrogen, along with small amounts of hydrogen and inert gases. In practice, it can be treated as if the medium were nitrogen; I think it’s fine to use a corrosion margin of 0.
Although the interior is an anaerobic environment during operation, there will always be periods of shutdown for maintenance, so I think a corrosion allowance still needs to be taken into account. Besides, the outside of this device also has to be exposed to the atmosphere
I think that, similar to determining the service life, when considering corrosion margin, manufacturing and usage factors also need to be taken into account. If a small margin is left, issues such as surface treatment before the equipment leaves the factory after production, or corrosion of the equipment’s interior due to the factory’s atmospheric conditions in case the equipment remains unused or is not properly maintained, can arise
The corrosion allowance depends on the properties of the media inside and outside your equipment as well as the level of protection in place. For example, if there is humid air inside the equipment, the corrosion allowance is 1 mm; in the case of an atmospheric environment outside, it depends on whether any protective measures are in use. If there is insulation inside the enclosure, the corrosion allowance can be 0 mm, whereas if there is no insulation and the equipment is exposed to the outdoors, the external corrosion allowance is 1 mm；
Actually, it depends on the expected lifespan of use; generally, for areas exposed to the outdoors, an estimate of 0.05 mm per year can be used
According to GB/T150.1, this is not acceptable; at least 1 mm should be used.
At least a 1mm corrosion margin needs to be considered.
Personally, I think that according to GB150, the minimum corrosion allowance should be 1
I took a look at the drawings for CPE Southwest; a corrosion margin of 2 mm was specified for both the nitrogen tank and the compressed air tank. 4 mm was taken for the wet natural gas containing carbon dioxide. What it gives me the impression of is that they all have a large margin of corrosion resistance.
According to GB150, 1 mm must be used – how is the cost control so good?