Does HG/T 20615 take corrosion margin into account for flanges?
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RT would like to first thank everyone for coming. Do HG/T20615 and HG/T20592 take corrosion allowance into account? If so, how much corrosion allowance is considered? Please feel free to share your thoughts
The margin is of course taken into account. As for how much, I don’t know
There have already been many discussions about this issue on the forum. I remember two main points: first, long-term practice has shown that the existing flanges are reliable; the grade of flanges chosen is generally much higher than the design pressure, ensuring sufficient strength. Second, the thickness at the small end is the same as that of the pipe fitting, and the allowance is the same as that of the pipe fitting.
The explanation on the second floor is absolutely correct. For European standard flanges, butt-welded flanges do not involve the issue of corrosion allowance (external corrosion is addressed through external anti-corrosion measures). The design of socket-welded flanges requires compliance with minimum S values, and this S value is the same as that of the pipe fittings; therefore, the amount of corrosion considered for the pipe corresponds to the amount of corrosion considered for the flange. The requirements are actually the same for American standards as those for European standards; the only difference is that for long-neck butt-weld flanges, the pipe wall thickness grade must be specified. The values listed in the table correspond to Sch40, and the flange’s wall thickness grade can be adjusted based on the wall thickness grade of the pipe, in order to meet the requirements regarding corrosion allowance.
China’s standards for flanged pipe fittings started developing late; many of the existing standards are direct copies of the European and American systems, which can be considered a shortcut. Corrosion allowance is certainly taken into account, after all these standards are copied from those of developed countries. Moreover, for WN flanges from the European system, China has increased the wall thickness of the fittings after adapting them, which makes them more reliable
Generally, the wall thickness of flanges and fittings is the same as that of the pipeline, so corrosion at the connection ends is already taken into account in the design of the pipeline.