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People often encounter situations where many design firms, construction companies, and purchasing organizations need to acquire seamless pipes of the Q355B, Q355C, D, and E steel grades, but specialists will say that these grades are not specified in the standards. At this point, many people get confused – how is there none? The national standard has already switched to the Q355 steel grade! ! ! First of all, there are simply too many standard numbers for national standards; these standards correspond, depending on the type of product, to round steel, steel plates, section steel, welded pipes, and seamless steel pipes. In terms of standard numbers, the elemental composition for round steel, steel plates, and section steels is generally governed by GB/T1591-2018; (since welded pipes are made from steel plates, the grade of the welded pipe corresponds to the grade of the base material, namely Q355) ； The standards applicable to seamless pipes include GB/T6479-2013, GB/T 8162-2018, and GB/T8163-2018. Additionally, in the 2018 version of standard GB/T 1591, the old grade Q345 has been replaced by Q355; however, the Q345 steel grade is still used in the 2018 versions of GB/T8162 and GB/T8163, as well as in the 2013 version of GB/T6479. This is why many people who inquire about seamless pipes made of Q355 receive the answer that this grade is not specified in the standards. Finally, it should be clarified in response to many people’s questions: since Q345 has been changed to Q355 in GB/T 1591, does that mean that Q345 in seamless pipes is actually Q355? ? “” The answer is no. In the 2008 versions of GB/T8162 and GB/T8163, it was specified that low-alloy steel should follow the GB/T1591 standard; however, in the 2018 version (as well as in GB/T6479-2013), it is clearly stated that the elements must meet the requirements specified in the standard. Therefore, there are certainly differences in terms of elements as well; the Q355 steel grade and the Q355N steel grade differ from each other, and the Q345 steel grade in Yu steel pipes also exhibits certain differences in terms of elements. Another reason is related to the actual mechanical properties of seamless pipes; when establishing standards, the yield strength threshold is set at Q345. Of course, it’s possible to achieve a strength level above Q355 through specific adjustments, but this requires following a technical agreement when custom-producing steel pipes. Naturally, the price in such cases will be higher than that of Q345-grade seamless pipes under the same standards. This is just my personal opinion; I welcome everyone to discuss it together and learn from each other.