Why does 316L have better resistance to external pressure than 304 and 316?
Thread Content
This post was last edited by zhangjuhua on 2018-9-1 at 10:47. At room temperature, the yield strength of 304 is 137 MPa, while that of 316L is 120 MPa. The elastic modulus values for both materials were checked using SW6, and they are the same. In the case of internal pressure and not very high temperatures, 304 generally performs better than 316L. However, in the case of negative pressure, such as -0.1 MPa, according to the calculations from SW6, 316L can withstand greater external pressure than 304 and has better pressure resistance. Why is this? -0.1MPA, DN1200x5; calculated length: 2500. Critical external pressure, i.e., pressure resistance: 316L > 304 > 316 > 304L
This post was last edited by zjq1962 on 2018-9-3 08:11. As the temperature rises, the material’s resistance to external pressure changes.
This post was last edited by fzujunru on 2018-9-1 09:51. The critical pressure for instability has nothing to do with the allowable stress of the material; their value of A is the same, but the value of B differs, resulting in different calculated thicknesses. It is primarily influenced by E. If you take a close look at the B curve in GB150.2, you will find that, for example, at 205 degrees, the values of E for 304 and 316L are different. The elastic modulus is related to both the chemical composition of the material and the temperature.
Different materials result in different parameters.
Let’s clarify the meaning of the external pressure curve graph: A represents the circumferential compression strain, while B is half of the circumferential compression stress. The relationship between A and B actually corresponds to the strain-stress diagram. At low temperatures, the compressive strength limit of 31603 is slightly better than that of 30408; therefore, 316 has a higher resistance to external pressure. However, this situation reverses at high temperatures. The allowable stress for stainless steel is based on its tensile yield strength, and therefore cannot be used as a comparison benchmark.
Thank you very much. I checked it, and there’s a point where B is equal to 1/2EA; in the old ASME standards, m was 4, but now B is equal to 2/3EA
Yes, I checked – the external pressure curve remains unchanged, but the safety factor for external pressure has changed from 4 to 3; therefore the value of b should be adjusted accordingly. Thank you for pointing this out
In terms of mechanical properties, not much consideration has been given to the differences between these materials; the main considerations are corrosion resistance and low carbon content. Let’s see your analysis.
For internal pressure, the material is primarily subjected to tensile stress, while under external pressure it is mainly subjected to compressive stress. The compressive and yield stresses for the same material are different; for example, in the case of cast iron