Issues regarding the operating environment of 20# steel
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There is a project currently under consideration, where 20# steel is used for the steam pipelines (operating at temperatures down to -20°C). However, the extreme environmental temperature in the location of this project is -45°C; it is estimated that such extreme temperatures occur for about 10 days during winter. There is concern now that, in the event of a shutdown of the equipment due to extreme weather conditions and a lack of steam in the steam pipelines, what problems might arise with the 20# steel used in such situations? Is there any problem with this material choice?
Extreme situations have not been encountered yet~~~~
The pipeline is not under pressure after shutdown, and it has an insulating layer on the outside, so there should be no problems.
Steam operation can be chosen; if that’s not possible, use heat tracing for the steam pipelines.
It has insulation, and good insulation is no problem
GB/T20801.2 \"Code for pressure pipelines – Industrial pipelines – Part 2: Materials\" stipulates that: (1) As specified in clause 8.1.1, the throttling effect of the fluid and the influence of ambient temperature shall be taken into account when determining the minimum design temperature； (2) According to the specifications for curve B in Figure 1 based on material category, the minimum operating temperature for carbon steel 20# material (without the need for impact testing) is -20℃ ； Under low-temperature and low-stress conditions, the minimum operating temperature for carbon steel is -101°C, and impact testing is exempted ； Lower temperature and lower stress service refers to a service condition that meets all of the following requirements: a) the maximum operating pressure at low temperatures is not more than 30% of the maximum allowable operating pressure at normal temperatures ； b) The total axial (tensile) stress in the pipeline, resulting from pressure, weight, and displacement, shall not exceed 10% of the minimum tensile strength specified in the material standards (the stress amplification factor is not taken into account when calculating the displacement stress) ； c) Limited to GC2 class pipelines, with a minimum design temperature of not lower than -101°C. Usually, the pipe temperature reaches -20°C during shutdown in the cold winter conditions; this situation occurs relatively rarely. Even when it does happen, it is under conditions of low temperature and low stress, so there is no need to use low-temperature steel – 20# steel will suffice
In extreme weather conditions, the equipment stops operating and there is no steam in the steam pipelines; in such a situation, is there also no pressure inside the pipes? Since there is no pressure, there should be no problem under stress-free conditions.
I think the same way. But once production stops, although there is no pressure and the pipes are at atmospheric pressure, in extreme conditions the pipes may contract; the original U-shaped bends will then be under compression, while in cold conditions they are under tension. Could low-temperature brittleness cause those U-shaped bends to break? Feel free to discuss with each other.
Slaying Demons and Evil Spirits, published on 2017-6-7 09:13. In extreme weather conditions, the equipment stops operating and there is no steam in the steam pipelines; in such a situation, is there also no pressure inside the pipes? Since there is no pressure, there is no stress… I think the same, but once production stops, although there is no pressure and the pipes are at atmospheric pressure, in extreme conditions the pipes may contract; the original U-shaped bends will then be under compression, while in cold conditions they are under tension. Could low-temperature brittleness cause those U-shaped bends to break? Feel free to discuss with each other.