What does the "L" designation mean?
stainless steel tube
The use of the letter L after the grade number(i.e 304L,316L) means that the carbon content is resisted to a maximum of 0.03%, in stainless steels that are not low carbon, maximum levels may be set at 0.08 to 0.15%. low crabon levels should be secified when sections 0.25 in (6mm) or heavier will be welded.  Specification of low carbon reduce the risk of sensitization and improves the weld'sthe corrosion resistance.

There is a common misconception that specifying low carbon will improve the corrosion resistance of surfaces outside the weld zone. This is not the case. Corrosion resistance is improved by specifying stainless steels with higher chromium, molybdenum and or mplybdenum levels. Specification of low sulfur(0.005% or less) may also improve corrosion performance.

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