Do you know Q345 and 16Mn steel for pressure vessels‘

Do you know Q345 and 16Mn steel for pressure vessels‘

In the air compressor industry, the most common pressure vessels are the gas storage tanks and the oil and gas barrels in the air compressor. So, do you know the material of these pressure vessels?

　　 First, let’s take a look at 16Mn. The name of 16Mn is the old national standard. Refers to 0.16% carbon content and manganese content (0.7%-1.0%). The new national standard does not require the manganese content of this material, so 16mn is not used to represent it. It is now classified as low-alloy high-strength structural steel. That is Q345 to be said next.

　　 Q345 is a low alloy steel (C<0.2%), which is widely used in construction, bridges, vehicles, ships, pressure vessels, etc. Q stands for the yield strength of this material, and the latter 345 refers to the yield value of this material, which is around 345 MPa. And as the thickness of the material increases, its yield value decreases.

The gas storage tanks of air compressors are generally made of Q345R and Q235. Q345 has good comprehensive mechanical properties, acceptable low temperature performance, good plasticity and weldability, and is used as medium and low pressure vessels, oil tanks, vehicles, cranes, mining machinery, power stations, and bridges. Such as structures, mechanical parts, building structures, general metal structural parts that bear dynamic loads, hot-rolled or normalized, and can be used for various structures in cold areas below -40°C.

　　 Pressure vessel steel Q345 and 16Mn, do you know?

　　 level classification

　　 Q345 can be divided into Q345A, Q345B, Q345C, Q345D, Q345E according to the grade. What they represent is mainly the impact temperature is different.

　　 Q345A level, it does not make an impact;

　　Q345B level, is 20 degrees normal temperature impact;

　　Q345C level, is 0 degree impact;

　　 Q345D level, is -20 degree impact;

　　Q345E level, is -40 degree impact.

　　In different impact temperature, the impact value is also different.

　　 contrast 16Mn

　　 Q345 steel is the replacement of the old grades of 12MnV, 14MnNb, 18Nb, 16MnRE, 16Mn and other steel grades, rather than just replacing 16Mn steel. In terms of chemical composition, 16Mn and Q345 are also different.

　　 More importantly, there is a big difference in the thickness grouping size of the two steel materials according to the different yield strength, and this will inevitably cause the change of the allowable stress of certain thickness materials. Therefore, it is not appropriate to simply apply the allowable stress of 16Mn steel to Q345 steel, and the allowable stress should be re-determined according to the new steel thickness group size.

　　 The ratio of the main constituent elements of Q345 steel is basically the same as that of 16Mn steel. The difference is that trace alloying elements of V, Ti and Nb are added. A small amount of V, Ti, Nb alloy elements can refine the grains, greatly improve the toughness of the steel, and the comprehensive mechanical properties of the steel have been greatly improved.

　　 Because of this, the thickness of the steel plate can be made larger. Therefore, the comprehensive mechanical properties of Q345 steel should be better than 16Mn steel, especially its low temperature performance is not available in 16Mn steel. The allowable stress of Q345 steel is slightly higher than that of 16Mn steel.