Electroslag welding (ESW) and electrogas welding (EGW) look nothing like SMAW or FCAW in practice — a rising pool contained by water-cooled copper shoes, a single continuous vertical pass through plate that would take dozens of arc-welding passes. They also look nothing like arc welding from a code compliance standpoint: AWS D1.1:2025 gives ESW and EGW their own essential variable table, separate from the Table 6.6 list that governs every other common process.

Shops that occasionally do heavy vertical plate work sometimes miss this distinction. Using Table 6.6 to establish or audit an ESW WPS is a compliance error — the requalification triggers are different processes.

What ESW and EGW are and when shops use them

Electroslag welding (ESW) starts with an arc to melt flux into a conductive slag bath. Once the bath reaches operating depth, the arc extinguishes and the process switches to resistance heating through the molten slag. Filler wire feeds continuously through the slag pool and melts at the bottom. The pool rises vertically as base metal and filler solidify behind it, contained by water-cooled copper dams on both faces.

Electrogas welding (EGW) maintains a conventional arc throughout. A gas mixture — typically CO₂ or CO₂/Ar blend — shields the pool, and the wire feeder system resembles FCAW-G more than it resembles true slag-bath processes. Copper shoes still contain the pool in the vertical groove.

Both are single-pass vertical processes. Neither can weld horizontal, overhead, or inclined joints — vertical upward is the only position.

Common applications in structural fabrication:

  • Plate girder web-to-flange welds on long runs
  • Heavy column base plate connections
  • Bridge pier cap beam splices
  • Thick pressure vessel shell seams (where the applicable code permits ESW/EGW)

The economics favor ESW and EGW when plate is thick and the vertical weld run is long enough to amortize tooling setup. On a 3-inch plate girder web with a 10-foot vertical seam, ESW can replace a full shift of FCAW multipass work with a single automated pass.

Table 6.7 — not Table 6.6 — governs ESW and EGW

AWS D1.1:2025 organizes PQR essential variables by process group:

  • Table 6.6 — SMAW, GMAW, FCAW, GTAW, SAW
  • Table 6.7 — ESW and EGW
  • Table 6.8 — Supplementary (CVN) for all processes

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

The 2020 edition used a different numbering: ESW/EGW essential variables were Table 6.6 in 2020. Under 2025, they shifted to Table 6.7 to make room for the expanded Table 6.6 arc-welding list. If your WPS is citing "Table 6.6" for an ESW procedure and your governing edition is 2025, the citation is wrong.

Key requalification triggers unique to Table 6.7:

  • Change in guide tube type — consumable vs. non-consumable guide tubes differ in how filler enters the pool and how arc initiation works. They are not interchangeable without requalification.
  • Electrode oscillation parameters — width, dwell time at each edge, and oscillation speed directly affect how heat is distributed across the plate face. Changes outside the qualified range require a new PQR.
  • Number of electrodes — adding or removing wire feeds changes deposition profile and heat distribution.
  • Dam (shoe) material or configuration — copper contact shoe vs. other configurations affect cooling rate and the resulting HAZ width.
  • Flux type (ESW) — flux composition affects slag conductivity, metal transfer, and bead profile. Flux types are not freely substitutable.
  • Shielding gas composition (EGW) — gas mixture changes affect arc stability and pool chemistry.

Compare this to Table 6.6, where variables like shielding gas percent or contact-tip-to-work distance are essential. Those variables don't appear in Table 6.7 because ESW/EGW pool dynamics make them less critical than the process-specific equipment variables above.

What a compliant ESW or EGW WPS must document

A standard AWS Annex M WPS form captures most arc-welding parameters, but ESW and EGW require additional fields that don't appear on the base form. A compliant WPS must document:

  • Electrode oscillation: width (in or mm) and dwell time at each edge
  • Guide tube type: consumable or non-consumable; if consumable, the guide tube specification
  • Number of electrodes and their arrangement across the joint width
  • Copper shoe/dam configuration: water-cooled; dimensions; any ceramic insert details used at plate edges
  • Rising speed range: pool travel speed in in/min or mm/min
  • Flux lot and classification (ESW) or shielding gas mixture (EGW)
  • Starting and run-off tab details: joint ends require controlled arc initiation and termination to avoid crater defects in the production weld

If your WPS software generates only a standard Annex M form with arc-welding fields, verify that a supplemental section or separate form captures the Table 6.7 variables. An ESW WPS with only standard arc-welding fields is incomplete.

CVN toughness concerns with ESW and EGW

High heat input is inherent to both processes. The HAZ is wide, grain growth is significant, and Charpy V-Notch toughness can be substantially lower than what the same base metal delivers with arc welding.

When a project specifies CVN testing, Table 6.8 supplementary essential variables apply on top of Table 6.7. ESW and EGW CVN qualifications are harder to pass than equivalent arc-welding qualifications. Post-weld normalizing — heat treatment to refine grain structure — is sometimes specified to restore toughness after ESW.

Before committing to ESW or EGW on a CVN-required project, verify whether normalizing is feasible for the member geometry, and whether the budget allows for it. A failed CVN test on a completed girder is an expensive problem.

See: CVN impact testing and AWS D1.1:2025 Table 6.8 supplementary essentials

No prequalified WPS option

SMAW, FCAW-G, GMAW (spray), and SAW can qualify as prequalified procedures under AWS D1.1 without a supporting PQR, provided joint geometry and other requirements are met. ESW and EGW have no prequalified WPS option. Every ESW and EGW procedure requires a qualifying PQR with production-representative test plates.

For thick-plate ESW, PQR test plates are large and expensive to fabricate and test. Tensile coupons, guided bend coupons, and (when CVN is required) impact toughness specimens must all be cut from the test plate weldment. Factor this qualification cost into project bids when ESW or EGW is under consideration.

See: What is a PQR and why does every procedure need one?

When ESW and EGW make sense — and when they don't

Use ESW or EGW when:

  • Base metal is ≥ ~1 inch (25 mm) thick in a vertical groove
  • The joint is a straight vertical weld — no inclination, no horizontal or overhead
  • The run length is long enough to recover tooling setup costs
  • CVN impact toughness is either not required, or normalizing is planned

Avoid ESW and EGW when:

  • The joint is inclined, horizontal, or overhead — these are not viable positions
  • CVN is required and normalizing isn't in scope
  • Plate thickness is under 3/4 inch (19 mm) — arc processes are faster and cheaper
  • The project specification restricts high-heat-input processes

For a detailed comparison of heavy-plate arc welding processes and their WPS implications, see SAW WPS for A516-70 thick plate: process, variables, and PQR requirements.

Managing ESW and EGW in a WPS library

ESW and EGW procedures are typically a small fraction of a structural shop's WPS library — most work is SMAW, FCAW, GMAW, or SAW. The challenge is that the Table 6.7 fields fall outside standard form templates, and a shop that goes months between ESW jobs may not remember which fields Table 6.7 requires.

Keeping the Table 6.7 variable list on the WPS document itself — not just in a separate checklist — makes audits straightforward. When a CWI reviews the ESW WPS, all required fields are present on the face of the document. See WPS Welding's procedure library features for WPS management that supports both standard and specialty process documentation.