Issues regarding the use of materials in refrigeration auxiliary equipment
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For the refrigeration units produced by our company, the working medium is R717, the design pressure is 2.0 MPa, and the design temperature is 50°C. Can Q235 series material be used? If liquid ammonia stress corrosion is taken into account, according to Article 6.7.4 of HG20581, I believe materials from the Q235 series cannot be used. However, as for refrigeration units, I would appreciate it if experts could advise me on whether these units meet the conditions for liquid ammonia stress corrosion
Q235C steel plates can be used, and the applicable conditions are as follows: when used for housings, the design pressure should be less than or equal to 2.5 MPa, the design temperature should range from 0 to 200°C, and the thickness of the steel plate should be less than or equal to 30 mm. It will not suffer from stress corrosion.
According to the interpretations in JB/T4750-2003, stress corrosion rarely occurs in the Q235 series; however, this is conditional on the material being in a state such as normalized + tempered, annealed, or quenched and tempered, as required by HG20581 for applications involving liquid ammonia stress corrosion. Since the Q235 series is in a hot-rolled state, it cannot be used in environments subject to liquid ammonia stress corrosion according to these regulations