Questions about hg/T20646.5-1999?

This is the answer given by AI: I’m not sure if it’s correct 1. Galvanic corrosion: In your design, the carbon steel flange and the stainless steel flange are connected by bolts, with gaskets in between. If the medium transported through the pipeline is conductive (such as water, especially seawater and industrial wastewater), or in a humid atmospheric environment, the medium will seep into the flange joint surface. Mechanism: When carbon steel (reactive) and stainless steel (inert) come into direct contact with an electrolyte, a galvanic cell is formed. Carbon steel, when used as an anode, accelerates corrosion. Consequence: Local corrosion occurs on the sealing surface of the carbon steel flange, creating leakage paths. This type of corrosion occurs on the sealing surface; it is extremely hidden and highly damaging, ultimately leading to fluid leakage. 2. Bolt load relaxation and leakage caused by thermal expansion: The thermal expansion coefficient of austenitic stainless steel is about 50% higher than that of carbon steel. Mechanism: When the operating temperature changes (for example, from room temperature to the operating temperature), the expansion amount of stainless steel flanges is much greater than that of carbon steel flanges. This uneven expansion will cause the bolts to experience additional stress, which may lead to them being stretched. This reduces the compressive force of the flange on the gasket (sealing specific pressure). Consequence: At high temperatures, flange joints are highly prone to leakage.

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