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How Electrode Designations Work

Every AWS filler metal designation encodes essential information about the consumable in a structured alphanumeric string. The designation tells the welder and engineer exactly what the electrode or wire is designed to do. Understanding this system is fundamental to writing a correct WPS and selecting the right consumable for the joint.

Take the most common structural welding electrode, E7018, as an example. Each character in the designation carries specific meaning:

The E prefix indicates an electrode consumable. The next two digits (70) represent the minimum tensile strength in ksi (70 ksi = 490 MPa). The third digit (1) indicates position capability: 1 means all positions (flat, horizontal, vertical, overhead), while 2 means flat and horizontal only. For E7018, AWS A5.1 Table 1 note a limits vertical and overhead welding to electrodes 5/32 in (4.0 mm) and under; larger sizes are not covered for vertical or overhead welding. The fourth digit (8) designates the coating type and current characteristics — in this case, an iron-powder low-hydrogen coating designed for AC or DC+ operation.

For GMAW/GTAW wire, the prefix changes to ER (electrode-rod), and the designation follows a different pattern. ER70S-6 breaks down as: ER = electrode/rod, 70 = 70 ksi tensile, S = solid wire, 6 = deoxidizer chemistry. For flux-cored wire, E71T-1 uses: E = electrode, 7 = 70 ksi, 1 = all-position, T = tubular (flux-cored), 1 = gas-shielded usability designator.

Key A5.x Specifications

AWS publishes separate A5.x specifications for each combination of base metal type and welding process. The table below covers the specifications most commonly referenced in structural steel fabrication under D1.1.

Classifications shown are designation names which are unchanged across editions; mechanical property requirements and testing methods may differ between editions. Always reference the edition specified in your contract documents.

The A5.36 Unified Designation System

AWS A5.36 represented a fundamental shift in how flux-cored and metal-cored electrodes were classified; AWS has since withdrawn the specification. Before A5.36, carbon steel FCAW electrodes fell under A5.20 and low-alloy FCAW electrodes under A5.29. These two specifications used different designation systems, making cross-referencing difficult and limiting the information encoded in the designation itself.

Under AWS A5.36:2016 Clause 3.4, electrodes classified under AWS A5.20, A5.29, A5.18 or A5.28 may also be classified under AWS A5.36 only when all requirements of each specification are met. Designation example: E71T1-C1A2-CS1

The shielding gas designator (C = CO2, M = mixed gas) tells the user exactly which gas the electrode was tested and classified with. A5.36 Figure 1 uses A for the as-welded heat-treatment condition and P for postweld heat treated. A5.36 Table 2 assigns Z when there is no impact requirement; designator 2 is −20°F. In E71T1-C1A2-CS1, A is as-welded and 2 is the −20°F impact class. The chemistry suffix (CS = carbon steel, NI = nickel alloy) provides information that required looking up supplement tables under the old A5.20 system.

Existing A5.20 and A5.29 designations remain valid for electrodes classified under those specifications. Note: AWS has withdrawn A5.36, and D1.1:2025 removed every reference to it, so an A5.36 designation is a historical lookup. D1.1:2025 still refers to A5.18, A5.20, A5.28 and A5.29 for electrodes that comply with them; when writing a WPS under D1.1:2025, reference the A5.18, A5.20, A5.28 or A5.29 classification the electrode meets.

Filler Metal on a D1.1 WPS

The filler metal classification is one of the most important entries on a welding procedure specification. Under D1.1, filler metal selection is governed by Table 5.7, which maps base metal groups to compatible filler metal groups. The filler metal must provide matching or overmatching strength to the base metal being joined.

For prequalified WPSs (Clause 5), the filler metal must be listed in Table 5.7 for the applicable base metal group. Using a filler metal outside of Table 5.7 requires WPS qualification by test under Clause 6. The WPS form requires three filler metal entries: the A5.x specification number (e.g., A5.18), the electrode classification (e.g., ER70S-6), and the manufacturer trade name or brand.

Filler metal is an essential variable under both Table 5.5 (prequalified WPS essential variables) and Table 6.6 (qualified WPS essential variables). A change in filler metal classification — for example, switching from ER70S-6 to ER70S-3 — requires a new or revised WPS. A change in A5.x specification (e.g., from A5.18 to A5.28) always requires a new procedure.

The filler metal classification also determines the preheat category under Table 5.11. Table 5.11 Category B covers SMAW with low-hydrogen electrodes, SAW, GMAW, and FCAW, including E71T-1 and E71T-11. Category A is limited to SMAW with electrodes other than low-hydrogen, such as E6013. This distinction directly affects fabrication cost and schedule, making the filler metal selection a critical early decision in WPS development.

"The filler metal selection is the first thing I check on a WPS. If the electrode classification does not match Table 5.7 for the base metal group, the WPS is non-compliant before the welder even strikes an arc. Most filler metal rejections I see are E71T-11 used where E71T-1 was specified — the self-shielded wire does not meet the hydrogen requirements for the application."

— Field observation, structural fabrication inspection practice

Filler metal classification under AWS A5 is the engineer’s responsibility per the WPS, but the welder is responsible for verifying the rod or wire heat number matches the WPS at every workstation. The most common shop floor error is using leftover filler from a different qualified procedure — heat number traceability is non-negotiable on D1.5 bridge work and increasingly enforced on D1.1 high-strength applications.

Calculate D1.5 Bridge Preheat →

— Welding inspector observation, fabrication shop, 2026