Dual Grade Wall Thickness Calculation 316/316L

I think you will find that there is an overlap in the requirements for chemical composition of 316 and 316 L. The L is generally taken to mean Low carbon. The problem is taht if you weld a stainless having more than a certain level of carbon, carbides may be formed at the surface and this initiates pitting corrosion in hostile environments - e.g sea water, sea water spray or even salt-laden fog or air. In fact environment having some chloride presence. Hence 316 L is often specified.

Since 316L has a lower strength (lower tensile and lower .2% proof stress which is often referred to as a yield stress) then the allowable stress values for 316L should be used.

There is a lot more to it so if you are doing anything for a critical application where damage could endanger life, then make sure you have your calculations checked by a piping engineer and have a materials expert confirm your material selection.