What are the similarities and differences between A105 flanges and 20 flanges in terms of application?
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What are the similarities and differences between A105 flanges and 20 flanges in terms of application?
A105 is a type of special steel, namely a cold-forged carbon steel designed specifically for manufacturing flanges. Its composition is as follows: C: ≤0.35, Si: ≤0.35, Mn: 0.6–1.05, S: ≤0.050, P: ≤0.040. 16Mn also belongs to the category of carbon-manganese steels, and it has mechanical properties similar to those of A105; however, the carbon content in A105 is slightly higher, while the manganese and silicon contents in 16Mn are slightly higher. Flanges made from 16Mn can be used as a substitute for those made from A105.
A gas transmission pipeline failed due to through-cracks that occurred during pressure testing at -16 ℃, using domestically produced A105 steel flanges； Optical microscopes, scanning electron microscopes, and material testing machines were used to analyze the chemical composition, microstructure, mechanical properties of the failed flange, as well as the formation and propagation of cracks, in order to determine the cause of failure. The results show that the material of the failed flange has a coarse microstructure, with a tendency to form Widmanstätten structure in certain areas; its plasticity and impact toughness are poor, failing to meet the standard requirements ； The crack originates at the root of the machining mark located at the stress concentration zone where the inclined surface of the flange neck meets the flat surface; under the combined effect of welding residual stresses and pipeline pressure, the crack propagates through the brittle material, ultimately leading to the failure of the flange.
20 refers to ordinary carbon steel flanges; the main differences lie in temperature and pressure. The operating environments need to be distinguished.
A105 belongs to the American standard, while 16Mn is a domestic steel grade. A105 has a slightly higher carbon content than China’s 20# steel; pipes used at temperatures around -16°C are generally made of 16Mn material, whereas the American standard corresponds to A333