Liquid ammonia stress corrosion environment and material processing

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I. The liquid ammonia medium in contact meets the following conditions to be considered a liquid ammonia stress corrosion environment: 1. The medium is liquid ammonia with a water content of no more than 0.2%, and in situations where it may be contaminated by air (oxygen or carbon dioxide). 2. The operating temperature should be above minus 5 degrees Celsius. II. Low-carbon steels and low-alloy high-strength steels (including welded joints) used in liquid ammonia stress corrosion environments shall meet the following requirements: 1. The yield strength σs specified in the material standards shall be ≤ 355 MPa. 2. The actual measured tensile strength σb of the material is ≤ 630 MPa. ' V6 |7 K+ P1 K+ G2 U 3; the material must be in at least one of the following conditions: normalized and tempered, annealed, or quenched and tempered. 4. Limit on carbon equivalent (when the carbon equivalent limit is exceeded, the frequency of testing the hardness limit should be increased) ； (A! a& a) Low-carbon steel and carbon-manganese alloys: CE≤0.40, 1 d* l6 P# k. F6 R5 Q; i b. Low-alloy steel: CE≤0.45, " R) v! P( ]# k( Y 5. For materials that are not welded or that have been heat-treated after welding, the hardness limits are as follows: a) Low-carbon steel: HV(10)≤220 (single value), * p$ Q- A# X! F# m' y b. Low-alloy steel: HV(10)≤245 (single value). 6. All welds must undergo welding procedure qualification, including butt welding, repair welding, welding of pipes to tube sheets, cladding welding, fillet welding, etc ； 7. Where strength requirements are met, low-strength welding materials should be used as much as possible ； & g( e0 }0 q* 8: The hardness limits for the welded joint (including the weld seam, heat-affected zone, and base metal) are the same as those specified in Article 5 ； 9. The starting and arc-forming points at the welds (including those in temporary welds) must be ground to a depth of more than 0.3 mm before post-weld heat treatment, and subjected to magnetic particle or dye penetrant inspection ； 10. Perform heat treatment after welding, or use a welding process that ensures the hardness does not exceed HB185 ； , @1 t5 11. Adding ≥0.2% water to ammonia as a buffer can also serve as an auxiliary measure to prevent stress corrosion cracking ；