E310-16 and E309L-16 are both stainless SMAW classifications, but they solve different problems. E310-16 is primarily a heat-resistant/high-alloy stainless choice associated with 310/314-type base metals and some transition-layer applications. E309L-16 is commonly selected for stainless-to-carbon or low-alloy steel dissimilar joints and 309-family work. Neither classification is a universal substitute for the other.
Use the classification as a screening step only. The governing WPS, code, base-metal grades, service temperature, corrosion exposure, post-weld heat treatment, and manufacturer data sheet control the final choice.
The practical difference
Hobart Brothers currently lists its 310 Sterling AP as AWS A5.4 E310-16 and describes it for joining 310 stainless and steels in the roughly 20-27% chromium / 18-22% nickel range, plus certain transition-layer uses. Hobart lists 309/309L Sterling AP as AWS A5.4 E309-16 / E309L-16 and specifically calls out dissimilar-metal welding such as 309 stainless to mild or low-alloy steel.
ESAB data points the same direction. ESAB’s OK 67.13 is classified E310-16, while Arcaloy 309L-16 and Sureweld 309L-16 are classified E309L-16 and are described for carbon or low-alloy steel to stainless applications, subject to service-temperature and procedure limits.
When E310-16 belongs on the shortlist
E310-16 belongs on the shortlist when the base metal or procedure specifically points to 310-family high-alloy stainless, heat-resistant service, or an approved transition-layer application. WSP’s exact E310-16 stick filler page identifies AWS A5.4, Stick/SMAW, and 310/314 heat-resistant stainless as the common base-metal path.
That does not mean E310-16 is automatically correct whenever a part “gets hot.” Elevated-temperature welding is a materials-engineering problem. Oxidation resistance, creep, thermal cycling, dilution, restraint, joint design, and the actual base alloy matter. If the drawing or WPS does not identify the filler, verify before welding.
When E309L-16 belongs on the shortlist
E309L-16 is a common screening choice for stainless-to-carbon steel or stainless-to-low-alloy steel transition joints and for 309-family stainless. WSP’s exact E309L-16 stick filler page identifies stainless-to-mild steel and 309 stainless as the common path.
The “L” indicates low carbon, but that does not remove the need to check service conditions. ESAB notes service-temperature limits for specific 309L products and warns that post-weld heat treatment requires due consideration. Those statements are product-specific manufacturer guidance, not blanket limits for every electrode carrying the classification.
Do not choose by chromium and nickel numbers alone
Classification chemistry helps explain why the two electrodes behave differently, but chemistry alone does not approve a joint. Manufacturer catalog values are usually typical deposit values, not the same thing as AWS specification limits. A typical chemistry number from one brand should never be copied into a WPS as though it were the classification boundary.
The same rule applies to tensile strength, elongation, ferrite, amperage, and deposition data. Treat manufacturer values as data for that product and diameter. Treat AWS classification requirements as specification requirements. Treat the WPS as the job’s controlling instruction when a qualified procedure is required.
A five-question selection check
First: identify both base metals by grade. If one side is unknown, do not assume 309L is automatically safe just because it is often used for dissimilar joints.
Second: identify the service temperature and environment. Heat-resistant service, corrosion service, pressure service, cyclic loading, or chemical exposure can change the acceptable filler.
Third: check the WPS, drawing, code, customer specification, or engineering instruction. If a qualified procedure names E310-16 or E309L-16, that requirement outranks a generic selection chart.
Fourth: verify the exact electrode product and diameter. Current type, polarity, amperage range, position, approvals, packaging, and storage instructions are product-specific.
Fifth: evaluate post-weld requirements. Heat treatment, machining, corrosion testing, ferrite requirements, or appearance requirements can make a seemingly reasonable substitution unacceptable.
Where the WSP Filler Metal Finder fits
The WSP Filler Metal Finder is useful for narrowing candidate classifications. It is not an approved procedure and does not replace material identification, a code requirement, manufacturer data, or engineering review. Use it to get to the right family faster, then verify the actual job.
You can also start from WSP Alloy Support when you know the process and general material family but not the exact AWS classification.
Common mistakes
One common mistake is using E309L-16 as a universal “mystery metal” electrode. Another is using E310-16 simply because the part sees heat without identifying the base alloy or duty cycle. A third is substituting one stainless electrode for another because the available rod “looks close.” Those shortcuts can change weld-metal chemistry, ferrite behavior, cracking sensitivity, corrosion performance, and heat-service performance.
Storage and handling still matter
Even the correct classification can perform poorly if the coating is damaged, contaminated, or improperly stored. Follow the electrode manufacturer’s storage and reconditioning instructions for the exact product. Do not invent a rebake temperature or time from memory; stainless covered electrodes vary by manufacturer and package system.
Bottom line
Choose E310-16 when the verified application points to 310-family/high-alloy heat-resistant stainless or an approved transition-layer use. Choose E309L-16 when the verified application points to 309-family or stainless-to-carbon/low-alloy dissimilar welding. If the base metals, service, or procedure are unknown, the correct result is Unknown — verify, not a guessed electrode substitution.
References
Hobart Brothers stainless filler overview
Hobart 309/309L Sterling AP
ESAB OK 67.13 — E310-16
ESAB Arcaloy 309L-16
WSP E310-16
WSP E309L-16
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