The shell of all chemical equipment is a container that bears the pressure, temperature, and chemical medium during the chemical process, ensuring long-term safe operation while also considering economy. Pressure vessel technology is a container that integrates applied mechanics, materials science, metallurgical technology, mechanical manufacturing technology, and technical physics, specifically used for pressure operations in chemical production. The structural characteristics of pressure vessels are usually composed of shell, head, connecting pipe, seal, support and other components. The material is mostly steel, and the manufacturing methods are mainly pressure processing and welding.
The welding joints of pressure vessels should be inspected for shape, size, and appearance quality before non-destructive testing can be carried out. Materials with a tendency towards delayed cracking should undergo non-destructive testing 24 hours after welding; Materials with a tendency towards reheat cracking should undergo non-destructive testing after heat treatment. The non-destructive testing methods for pressure vessels include radiographic, ultrasonic, magnetic particle, penetrant, and eddy current testing. The pressure vessel manufacturing unit shall select the testing method and testing length according to the design drawings and relevant standards. The non-destructive testing ratio of pressure vessel butt welded joints is generally divided into two types: complete and partial (greater than or equal to 20%). For low-temperature vessels made of ferritic steel, the proportion of local non-destructive testing should be greater than or equal to 50%.
The pressure test of pressure vessels is divided into water pressure test and air pressure test. When it comes to the materials of various components of pressure vessels, such as cylinders, heads, fittings, flanges, fasteners, etc Different, in the calculation of pressure tests, the small []/[] t ratio of each component material should be taken.
Before the pressure test, the fastening bolts of the connecting components of the pressure vessel must be fully assembled and correctly tightened. The pressure gauge used for testing shall comply with the relevant provisions of Chapter 7. At least two calibrated pressure gauges with the same range should be used and installed on the top of the tested container for easy observation.
There should be reliable safety protection facilities at the pressure test site, which have been inspected and approved by the technical director and safety department of our unit. During the withstand voltage test, no work unrelated to the test shall be carried out, and unrelated personnel shall not stay at the test site.
The requirements for hydrostatic testing of pressure vessels are as follows:
(1) Any liquid that does not pose a danger during the testing process can be used as a hydraulic test medium at temperatures below its boiling point. Generally, water is required. When using flammable liquids for hydrostatic testing, the test temperature must be lower than the flash point of the flammable liquid, there must be no fire source near the test site, and appropriate fire-fighting equipment should be equipped.
(2) The water used for hydrostatic testing should be clean. When using water for hydrostatic testing of austenitic pressure vessels, the chloride ion content in the water should be strictly controlled to not exceed 25mg/L. After passing the test, the water stains should be immediately cleaned.
(3) The pressure vessel should be filled with liquid, and the trapped gas in the pressure vessel must be discharged. The outer surface of the pressure vessel should be kept dry, and when the wall temperature of the pressure vessel approaches the liquid temperature, the pressure can be slowly increased to the design pressure. After confirming that there is no leakage, continue to pressurize to the specified test pressure, hold for 30 minutes, and then reduce to 80% of the specified test pressure, hold for enough time for inspection. During inspection, the pressure should be kept constant and continuous pressurization is not allowed to maintain a constant test pressure. During the hydrostatic test of the container, it is not allowed to tighten bolts under pressure or apply external force to the compressed parts.