What are the differences between E309 and E309L electrodes?

Answer 1

The "L" suffix signifies this is the low carbon variant on this grade. See the composition limits listed in the material standard ASME Section II Part C for stainless steels in SFA 5.4 and 5.9

The low carbon grade is often used to protect from intergranular corrosion.

Answer 2

E309 electrodes are designed for welding stainless steel to carbon steel, while E309L electrodes are specifically designed for welding stainless steel to stainless steel. The "L" in E309L indicates a lower carbon content in the electrode, which reduces the risk of carbide precipitation and increases resistance to intergranular corrosion in the heat-affected zone.