The stress corrosion environment of liquid ammonia

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The liquid ammonia medium in contact with the container 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. 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+ P1K3; the material must be in either normalized + tempered, annealed, or quenched and tempered condition. 4. Limit on carbon equivalent (when the carbon equivalent limit is exceeded, the frequency of testing the hardness limit should be increased) ； a Low-carbon steel and carbon-manganese alloys: CE≤0.40. d b Low-alloy steel: CE≤0.455. 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). 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 ； 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 striking points at the welds (including those on temporary welds) must be ground to a depth of more than 0.3 mm before post-weld heat treatment, and magnetic particle or coloring inspections must be carried out ； 10. Perform heat treatment after welding, or use a welding process that ensures the hardness does not exceed HB185 ； 11. Adding ≥0.2% water to ammonia as a buffer can also serve as an auxiliary measure to prevent stress corrosion cracking.