Hello tayyabeme,
I was a vessel engineer for part of my life. The principle for 304L/316L to be dual certified are twofold:
1 That the carbon content meets the requirements for L grade, and,
2 that the mechanical properties meet the requirements for non L grade
Steel makers are able to fine tune the chemical contents or stainless steel, and at the same time get good mechanical values. If you look at an MTR (Material Test Report) for a dual certified material, glance at the mechanical properties.
Carbon controlled stainless steel is has better welding qualities, with less likelihood of forming chromium carbide, which is bad news.
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Sincerely,
Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM