Galvanized coatings protect structural steel from corrosion, but they create real welding problems: porosity, zinc fume hazard, and in high-restraint joints on thick material, potential heat-affected zone cracking. Structural steel shops that weld galvanized members — HVAC equipment curbs, industrial platforms, conveyor structures, railing systems — need a WPS that addresses the coating, not one written for bare steel that happens to get applied to coated material.
AWS D1.1 does not prohibit welding galvanized steel, but it requires that coatings harmful to weld quality be removed from the weld zone before welding.
What the zinc coating does to the weld
Hot-dip galvanizing (ASTM A123) applies a zinc layer typically 45–85 µm (0.0018–0.0033 in) thick to the steel surface. Zinc-primed steel — inorganic zinc silicate (IOZ) or organic zinc-rich primer — has a thinner coating but behaves similarly in the weld zone.
Porosity. Zinc boils at approximately 907°C. Weld pool temperatures are 1500°C and higher. As the arc contacts zinc-coated steel, the zinc vaporizes and injects gas into the pool. That gas must escape before the pool solidifies or it becomes a weld discontinuity. Porosity from zinc shows as surface pitting, subsurface voids on RT, or irregular cross-section on macroetch.
Lack of fusion. A heavy zinc layer ahead of the arc can act as contamination at the root of a fillet weld, interfering with fusion to the base metal. This is especially common at fillet weld roots where the arc doesn't directly heat the vertical leg before the pool advances.
Zinc fume. Zinc oxide fume is a respiratory hazard. Metal fume fever — chills, fever, and muscle aches presenting 4–8 hours after exposure — is the primary acute health effect. OSHA's zinc oxide permissible exposure limit (PEL) is 5 mg/m³ as an 8-hour TWA. Welding galvanized steel in an enclosed bay without exhaust ventilation routinely exceeds this. Local exhaust ventilation (LEV) positioned at the arc or supplied-air respirators are required — this is a legal compliance issue, not an optional precaution.
HAZ cracking. On high-restraint joints on thick-section material, molten zinc can penetrate grain boundaries in the heat-affected zone and cause intergranular cracking, known as liquid metal embrittlement (LME). LME is more common when welding austenitic stainless steel near zinc, but it has been documented on structural carbon steel in high-restraint configurations. Elevated preheat and slower weld sequences reduce susceptibility.
What the WPS must cover
A WPS for welding galvanized steel must explicitly state the coating condition and the pre-weld preparation requirement. A WPS that says "A36 plate" in the base metal field and says nothing about coating is a documentation failure. The inspector who picks up that WPS doesn't know whether to grind.
Base metal entry. Note the grade and coating specification. "ASTM A500 Gr B, hot-dip galvanized per ASTM A123" is a complete base metal entry. "A500 Gr B" is not — it leaves the coating condition unaddressed.
Pre-weld preparation. State the coating removal requirement explicitly: minimum grinding distance from the weld centerline, acceptable removal methods (grinding, wire brushing, flame burning), and the surface condition required after removal. A typical requirement is grinding the zinc from at least 2 in (50 mm) from each side of the joint line, to bare shiny metal.
Flame burning zinc off with an oxy-acetylene torch is an alternative to grinding for through-thickness removal. It is faster on large areas but requires care not to overheat the base metal and must still be followed by a surface inspection before welding. Include this option in the procedure if your shop uses it — a welder who burns the zinc but has no written authority to do so is in a procedural gap.
Preheat. Running preheat 25–50°F above the code minimum for the base metal grade reduces porosity and improves weld quality on galvanized steel. The slower cooling rate gives zinc vapor more time to escape the pool before solidification. This is a procedure judgment call informed by experience — it isn't a hard code requirement — but it should be documented in the WPS's preheat range rather than left to welder discretion. See preheat and interpass temperature on a WPS for how to document preheat ranges effectively.
Technique. Stringer beads generally outperform weave beads on zinc-coated base metal. Stringer passes travel faster and spend less time dwelling over any one area, reducing the quantity of zinc vapor the arc ingests per pass. Wide weave beads over a zinc-coated surface ahead of the arc accumulate more contamination.
Post-weld inspection for zinc-contaminated welds
Visual inspection of a galvanized-steel weld looks for:
Surface porosity. Small pits or craters on the weld face or weld toes. Any surface porosity outside D1.1 acceptance criteria is a rejection. See visual acceptance criteria under AWS D1.1 for the specific limits.
Irregular bead profile. Zinc vapor often produces irregular spatter and uneven bead profiles. An irregular bead on a galvanized-base-metal weld may indicate contamination even where surface porosity isn't obvious — check the procedure compliance and pre-weld prep records.
Undercut. Zinc contamination can increase undercut tendency at the weld toe. Undercut breaks the toe profile and concentrates stress at a notch — visually inspect all weld toes on galvanized welds with more care than you would on clean-steel welds.
Weld toe cracking. On high-restraint joints, inspect the HAZ adjacent to the weld toe with MT for LME cracking. A weld that passes visual may still have subsurface grain-boundary cracking if conditions were right for LME.
If the project requires RT, internal porosity from zinc shows up as clustered round indications. A weld that passes visual may fail radiographic acceptance criteria for internal porosity. Consider running an RT or cross-section macroetch on first-off welds to validate the procedure before committing to the full production run.
Coating restoration after welding
The zinc coating within 2–4 in of the weld joint was removed before welding. That area is now bare steel and will begin rusting within days in a humid environment. Corrosion protection must be restored:
Cold galvanizing compound (zinc-rich paint). The most common field repair. Applied by brush or spray, it provides partial galvanic protection through zinc-dust pigment in the coating. Multiple coats build thickness.
Thermal spray zinc metallizing. Closer in performance to hot-dip galvanizing but requires specialized spray equipment. Used for more demanding corrosion environments.
The choice of restoration method is typically an owner or contract specification item — check the project's protective coating specification rather than defaulting to whatever is in the shop's supply cabinet.
Common WPS mistakes on galvanized steel
Using a clean-steel WPS without modification. The base metal grade matches (A36, A500), but the coating condition changes everything about pre-weld prep, preheat judgment, and post-weld inspection. The WPS must address the coating. See common WPS mistakes for similar oversights that appear across procedure types.
No pre-weld prep requirement in the WPS. The welder knows to grind, but it isn't written down. There's nothing for the CWI to verify compliance against, and there's no defense when an auditor or owner inspector asks for evidence that the coating was removed.
Preheat set to the code minimum only. No margin for the contamination variable on material where contamination is predictable.
No ventilation provision noted. Not a welding essential variable and not required to be in the WPS by D1.1, but its absence in any project record is a liability gap when an AISC or third-party auditor reviews the shop's safety practices alongside its WPS package.
For a WPS library that lets you fork a base procedure and document coating-condition variants cleanly, see welding procedure library, audit-ready. For help evaluating whether your shop's current WPS management handles galvanized and specialty base metals, see pricing.
Rule library based on AWS D1.1:2025; verify against your governing edition.