Weld Restart Procedures for Interrupted Passes: AWS D1.1

Every welder stops mid-pass eventually — an electrode burns out, a shielding gas bottle empties, a safety issue demands the arc be dropped immediately. The restart that follows is where a significant fraction of structural weld defects originate: a crater that was never filled, a cold lap where old and new weld metal met without fusion, a slag inclusion locked under the restart bead.

AWS D1.1:2025 workmanship requirements in Clause 7 apply to every portion of every weld pass, including restarts. The code does not carve out an exception for "that spot where I changed my electrode." Understanding what the code requires — and what a CWI should look for — prevents buried defects that pass final visual inspection but fail UT or show up as field cracking later.

Why Restarts Create Defects

When an arc goes out mid-pass, the weld pool freezes rapidly and forms a crater. Craters are structurally problematic for several reasons:

Crater cracking: Metal contracts as it solidifies. When the weld pool is large and cools with no additional filler, the crater shrinks faster than the surrounding weld metal, creating longitudinal or star-shaped crater cracks. These may be only a few thousandths of an inch wide — invisible visually — but are genuine crack defects that must not be buried under subsequent passes.

Oxidation of the crater edge: The instant the arc goes out, the cooling weld surface oxidizes. On SMAW and FCAW passes, a slag lip forms at the crater edge. Restarting over an oxidized, slag-covered crater without cleaning it first traps oxide and slag inclusions at the fusion interface.

Cold start — insufficient preheat at the restart point: The first fraction of a second after re-striking, the arc heats the base metal and the cold crater edge. If the welder moves forward immediately, the restart zone sees less heat than the rest of the pass, resulting in a narrow band of under-heated fusion at the crater edge. This becomes a subsurface void or cold lap.

Lack of fusion behind the restart: If the welder starts the arc ahead of the crater and moves backward to fill it, the toe of the new bead may not achieve full fusion with the far wall of the crater. The fill looks complete on the surface but is hollowed underneath.

Proper Restart Technique by Process

SMAW (Shielded Metal Arc Welding)

After an electrode change, the new rod should be struck on the base metal ahead of the crater — 1/2 to 1 in. past the crater in the direction of travel — then swept back through the crater to fill it completely. This backstep technique ensures the electrode is arc-established and the tungsten (actually tip of the rod) is hot before it contacts the cold crater. Once the crater is filled to the full cross-section and fusion is visible across the full width of the weld, the pass continues forward.

Do not restart directly in the crater with a new electrode. The cold strike in the crater fails to provide enough heat at the start to achieve proper fusion at the crater bottom — the coldest part of the restart zone.

Before restarting any SMAW pass on a code-critical joint, chip and brush all slag from the crater. Trap no slag under the restart bead.

FCAW-G and GMAW

Wire processes do not have the electrode-change interruption, but they have their own restart scenarios: wire tangle, tip change, gas hose kink, or deliberate stop for joint repositioning. Restart technique is the same principle — re-establish the arc ahead of the crater, travel back to fill, then proceed.

For high-consequence joints (moment connections, demand-critical welds), many quality programs require grinding the crater flat before restarting, removing the oxidized surface layer and any crater cracking. The time to do this during in-process welding is far less than the rework required if a crater crack is found during NDE after all passes are complete.

SAW (Submerged Arc Welding)

SAW restarts are managed differently in production. For seam welds on plate girders or long structural members, run-off tabs at the ends of the weld joint take the crater entirely off the structural component. For mid-joint restarts — unavoidable when a wire reel runs out during a long pass — the SAW WPS should specify the restart procedure explicitly: grind the crater, clean the area, restore flux to the restart zone, and re-arc. SAW flux contamination at a restart point is a particular concern — wet or degraded flux at the restart can introduce hydrogen and inclusions.

Pre-Restart Preparation Requirements

Whether the pass is SMAW, FCAW, or SAW, the welder should perform these steps before restarting any structurally significant weld pass:

  1. Inspect the crater for cracks. Visually examine the crater under adequate lighting with magnification if available. Any crack originating from the crater must be ground to sound metal before restarting — weld metal placed over a crater crack becomes a buried defect. On hydrogen-sensitive steels, use a grinder rather than arc gouging to remove crater cracks.

  2. Remove slag and oxidation. Chip and wire-brush the crater completely. On FCAW and SMAW, there should be no visible slag or oxide film on the crater surface before the arc is re-struck. On GMAW, remove any silicate islands (glass-like residue at the weld toes of the stop crater).

  3. Verify preheat at the restart point. The base metal adjacent to the restart must be at or above the minimum preheat temperature specified in the WPS at the moment the arc is re-struck. If the interruption was long enough for the base metal to cool below minimum preheat — common in cold shop environments, for thick plates, or for high-preheat requirements on A913 or A514 steel — the area must be re-preheated with a torch before proceeding.

    Checking preheat at a restart is as important as checking it before the first arc strike of the joint. For measurement methods and documentation, see Preheat Verification Methods for AWS D1.1 Field Welding.

  4. Check for moisture or contamination. Rain, condensation, or cutting oil that migrated into the crater during the work stoppage must be removed. For low-hydrogen processes (E7018, FCAW with low-hydrogen designator), any moisture pickup can defeat the hydrogen control benefit of the electrode selection and WPS preheat.

CVN Impact Test Zones and Restart Exclusions

When a WPS includes a CVN (Charpy V-Notch) impact toughness requirement — driven by cold service conditions or demand-critical welds under AWS D1.8 seismic provisions — the location of weld restarts becomes critical.

AWS D1.1 requires that CVN specimen notch locations in PQR test coupons be located away from weld starts and stops. The heat cycle, grain structure, and residual stress at a restart differ from the continuous weld, and CVN specimens from restart zones would not represent the weld properties being qualified.

In production, the project QC plan for demand-critical welds and cold-service applications should identify CVN exclusion zones: areas where weld restarts are not permitted without special preparation and documentation. Where restarts are unavoidable within such zones, the location must be recorded on the weld traveler, inspected for crater cracking before continuation, and flagged for targeted NDE.

For more on CVN supplementary essential variables and how preheat and interpass temperature changes interact with CVN qualification, see CVN Supplementary Essential Variables Under AWS D1.1 Table 6.8.

CWI Inspection of Restart Zones

In-process inspection is the most effective tool for catching restart defects before passes are buried.

During welding:

  • Observe starts and stops where staging allows. Visual monitoring of restart technique catches cold laps before the arc moves past the restart zone. A visually identifiable cold lap — a smooth, unfused ridge where the weld surface from two different arc-on periods meets without blending — should stop work immediately for grinding and re-welding.
  • Watch for "bridge-over" restarts: the welder starts ahead of the crater, bridges over it, and the crater void remains underneath the new bead. This is visible during welding but invisible after the pass is complete.

After each pass:

  • Examine restart points during interpass inspection. On SMAW and FCAW, the restart location often shows a slight crown change or bead width transition. Use this as a targeting indicator and examine the area closely.
  • Use magnetic particle testing (MT) on root pass restart locations in high-consequence joints before burying them with fill passes. MT on the root pass is far more practical than attempting to find a buried crack with UT after the joint is complete. For a reference on MT procedure and acceptance, see Magnetic Particle Testing: AWS D1.1 Structural Welds.

Documentation:

  • Record restart locations on the weld traveler or weld map for joints requiring full UT or PAUT coverage. The NDE technician should give restart locations extra attention during scanning.
  • On any restart where crater cracking was found and ground out, record the depth of grinding, the re-weld action taken, and the post-repair inspection result.

What the WPS Should Say — and What the QC Plan Should Add

The WPS specifies process, electrode, current range, travel speed, position, and preheat. Restart technique is workmanship, not a procedure parameter, and does not typically appear in the WPS text itself.

A well-structured quality program supplements the WPS with a shop welding instruction (SWI) or quality control plan that addresses:

  • Required crater fill at stops (fill craters to full cross-section before dropping the arc where physically possible)
  • Mandatory grinding at restarts in high-restraint or CVN-critical joints
  • Prohibited restart locations by connection type or structural member designation
  • Documentation requirements for mid-joint stops on primary structural members

Building these instructions into the QC plan — rather than relying on verbal instructions — ensures consistent practice across shifts and operators. For guidance on structuring a comprehensive weld QC plan and WPS library for your shop, see Interpass Temperature Control in Structural Welding and our WPS management tools.

Rule library based on AWS D1.1:2025. Verify against your governing edition — the AHJ or contract may specify 2020 or an earlier edition.