AWS A5 filler metal classifications decoded for WPS

The classification printed on an electrode box or wire spool encodes most of what you need to know about that filler metal — minimum tensile strength, welding position capability, coating or flux type, shielding gas requirement, and diffusible hydrogen level. Reading it correctly is a prerequisite for writing a WPS that passes inspection and specifying the right material for the qualified procedure.

This breakdown covers the classifications most commonly used in AWS D1.1 structural fabrication: SMAW, GMAW solid wire, FCAW, and SAW.

The AWS A5 Family

AWS publishes separate filler metal specifications for each welding process. The ones relevant to D1.1 structural work:

The WPS identifies the filler metal by its full classification, referencing the applicable A5 standard. When a CWI or auditor checks filler metal on the shop floor, they compare the packaging to the WPS classification. Mismatches — including a wrong suffix — are non-conformances.

SMAW: Breaking Down E7018-H4

E7018-H4 is the most common low-hydrogen SMAW electrode in structural fabrication. Reading left to right:

E — Electrode suitable for electric arc welding.

70 — Minimum tensile strength of deposited weld metal: 70,000 psi (70 ksi). E80 and E90 series indicate 80 and 90 ksi minimum, respectively.

1 — Usable welding positions. 1 = all positions (flat, horizontal, vertical-up, overhead). 2 = flat and horizontal only. 4 = flat, horizontal, and vertical-down.

18 — The last two digits define the coating type and compatible current. The 18 combination = iron powder low-hydrogen potassium coating, suitable for AC or DCEP. Other common pairings: 15 = low-hydrogen sodium, DCEP only; 16 = low-hydrogen potassium, AC or DCEP; 10 = cellulosic-sodium high penetration, DCEP only.

-H4 — Diffusible hydrogen designator per AWS A4.3. H4 = ≤4 mL/100 g. H8 = ≤8 mL/100 g. H16 = ≤16 mL/100 g. The WPS specifies the H-class required based on the base metal, thickness, preheat level, and connection type. For handling and storage requirements tied to each class, see low hydrogen electrode conditioning H4 H8 H16.

For a complete walkthrough of how these parameters translate into a qualified procedure, the article on a SMAW low-hydrogen E7018 WPS covers the process-specific essential variables.

GMAW Solid Wire: ER70S-6

E — Electrode (can carry welding current).

R — Rod. The ER prefix means the wire can be used as an electrode in GMAW or as a filler rod in GTAW. Same classification applies to both uses.

70 — 70 ksi minimum tensile strength of deposited weld metal.

S — Solid wire (as opposed to tubular or cored wire).

6 — Chemistry designation. AWS A5.18 defines the composition range for each suffix. The S-6 composition includes higher silicon (0.80–1.15%) and manganese (1.40–1.85%) than S-3 or S-2. The additional deoxidizers clean the weld pool more aggressively, making ER70S-6 the standard choice for hot-rolled structural steel with typical mill-scale surfaces.

There is no H-class suffix for solid GMAW wire because diffusible hydrogen in GMAW is governed by shielding gas moisture content and base metal surface condition rather than electrode coating.

FCAW: E71T-1C and the T-Designator System

FCAW classifications come from AWS A5.20 (carbon steel) or A5.29 (low-alloy). The decoding:

E — Electrode.

7 — 70 ksi minimum tensile strength. Note: single digit for FCAW (7 = 70 ksi), unlike the two-digit SMAW system (70 = 70 ksi).

1 — All-position capability. The digit before T: 1 = all positions, 0 = flat and horizontal only.

T — Tubular. The wire has a flux-filled core rather than a solid cross-section.

-1 — Usability designator. This is the key digit for specifying the electrode type:

• T-1: Rutile core, multi-pass capable, requires external shielding gas (CO2 or mixed)
• T-5: Basic slag, DC+ polarity, shielded; low slag volume, good for positional work
• T-8: Self-shielded (no external gas), low hydrogen — classified to a maximum hydrogen level
• T-11: Self-shielded, all-position, no CVN impact test requirement in the base specification
• T-12: Low hydrogen, shielded, CVN-tested

C or M — Shielding gas qualifier. C = 100% CO2. M = 75% Ar / 25% CO2 mixed gas. No suffix = self-shielded (T-8, T-11 types that require no external gas).

E71T-1C: rutile, all-position, multi-pass, CO2-shielded — the most common D1.1 structural FCAW electrode.

Switching shielding gas from CO2 to mixed without requalifying the WPS is a frequent field mistake. A T-1C wire run on mixed gas, or a T-1M wire run on straight CO2, represents a change from the qualified procedure and requires a documented WPS revision or requalification.

SAW Flux-Electrode Combinations: F7A2-EM12K

SAW is different from the other processes — the flux and electrode work together to determine weld metal chemistry and mechanical properties, so the classification covers both components.

F — Flux.

7 — 70 ksi minimum tensile when this flux is paired with this electrode.

A — Condition of the test weld. A = as-welded (no post-weld heat treatment). P = post-weld heat-treated condition.

2 — Charpy V-Notch temperature classification. The digit corresponds to the test temperature: 2 = –20°F (–29°C). Other designations: Z = 0°F, 3 = –40°F, 4 = –60°F. If the digit is absent (some older classifications), no CVN requirement was tested.

E — Electrode (the solid wire component).

M12K — Electrode chemistry: M = medium manganese, 12 = nominal 0.12% carbon, K = silicon-killed (deoxidized with silicon).

The SAW classification is always a combination — F7A2-EM12K means this specific flux tested with this specific electrode met those mechanical properties. Substitute either component and you have a different classification that must be tested independently.

The A5.36 Change in D1.1:2025

AWS A5.36 introduced a performance-based classification system that gives manufacturers more flexibility in filler metal composition, using an open designation format (ExTx-x) rather than the fixed chemistry ranges of A5.20 or A5.29. The tradeoff is that the open composition range makes it harder to verify that a filler metal with a specific A5.36 designation meets the essential variable requirements of a given WPS.

In the 2025 edition, AWS D1.1:2025 Table 6.6 row 4 removed A5.36 from the preapproved list of GMAW/FCAW filler metals. Electrodes classified under A5.36 may still be used under D1.1:2025 but require additional qualification steps rather than relying on preapproval. For the full impact of this change on existing WPS libraries, see the dedicated article on new A5.36 designator rules in 2025.

Rule library based on AWS D1.1:2025; verify against your governing edition.

Using the Classification to Verify WPS Compliance

On every filler metal check in the field or shop:

1. Read the full classification from the product label — including all suffix designators
2. Compare it character-by-character to the filler metal field in the WPS
3. Confirm the heat or lot number is recorded in the weld traveler
4. For CVN-qualified or D1.8 demand-critical procedures, verify the manufacturer's certificate of conformance is on file for the specific lot

A classification mismatch does not mean the weld is defective, but it is a paperwork non-conformance that requires engineering disposition before the joint is accepted. Catching it at material receipt — before the wire is on the machine — costs nothing. Catching it during final audit costs significantly more.

Shops managing multiple WPS procedures across different processes and base metals benefit from having the filler metal classification linked directly to the WPS record so the comparison is automatic rather than manual. If you want to see how that tracking works in practice, WPS software with filler metal compliance checking eliminates the classification lookup step entirely.