The 20# steel pipe was replaced with 304
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For a certain project, the chilled brine pipelines operate at temperatures ranging from 0 to -40 °C; the owner originally used 20# steel pipes. The designer asked me if it was possible, because standards such as GB/T20801 and SH/T 3059 specify that 20# steel pipes specified in GB/T8163 can only be used at temperatures down to -20 ℃. I said that this is a refrigeration pipeline, and it should comply with the regulations of the refrigeration industry. He said that once inside the factory, there are industrial pipelines, and regulations such as TSGD0001 must be followed.
I said that GB/T20801 covers conditions of low temperature and low stress, while SH 3501 provides classifications for pipes used in low-temperature environments; you can use these as references. Also, communicate with the HVAC team. A few days later, he said that for the HVAC field, due to the large cooling capacity and a wide variety of options, there are currently no economically viable materials available. I gave it to him – it was a material choice I had used before; I selected 16Mn (Q345). I told him to keep it as a provisional decision for now and to consider it further later on.
It’s better to follow the standards from the start; otherwise, trying to save money by cutting corners or using inferior materials will lead to serious problems down the road.
This is not about cutting corners or using inferior materials; rather, it’s a problem of excessive costs, with pipe prices increasing by n times. Moreover, 304 steel is not resistant to chloride ions, and unfortunately, frozen brine contains substances such as calcium chloride.
Are there many such manufacturers in the country these days, raising prices layer by layer? There’s nothing you can do about it.
When the pipeline grade table came out, I took a look and was surprised: for frozen brine pipelines at 0–50 °C, 304 material is used. I asked about a device designed by a former colleague; the temperature of the chilled saline pipeline had dropped. But I checked, and the temperature of the cryogenic brine pipeline in that device was also only -40 °C – there was no change.
monel for salt water
Can pipes made of Q345E be used?
An experienced mentor once told me that it seems this standard applies as well as that one; when in doubt, use the one with the higher requirements.
It is best to use 304; if carbon steel is used for the frozen saline, it is prone to scaling and rusting, which can affect the quality of the saline. Depending on the temperature, low-temperature steel could be considered, but its procurement time is relatively long.