Why shielded metal arc welding can experience arc blow from magnetic fields

Outline:

• Hook: A sparky little tale about an arc that wanders when magnetic forces show up.

• What arc blow is and why SMAW is particularly prone:

• The basics: magnetic fields, current path, and how SMAW’s setup plays into it.

• The role of DC polarity and grounded workpieces.

• How SMAW stacks up against TIG, SAW, and GMAW:

• Why SMAW is more susceptible than TIG (consumable electrode vs. non-consumable).

• How flux shielding in SAW and the wire feed in GMAW mitigate some magnetic effects.

• Real-world cues and practical fixes:

• Early signs, common scenarios (thick material, pipe, walls, DC polarity, ground placement).

• Straightforward remedies: repositioning ground, polarity tweaks, shielding, and geometry changes.

• Quick tips you can actually use:

• Grounding habits, electrode choice, joint design ideas, and situational awareness.

• Wrap-up: Arc blow isn’t a monster—it's a signal you can read and control.

Shielded Metal Arc Welding and the Curious Case of Arc Blow

Let me tell you a quick reality you’ll hear welders mention in the shop: the arc isn’t always a straight little light show the moment you pull the trigger. Sometimes it seems to drift, wander, or even bow away from the bead. That wandering is what we call arc blow. It happens when magnetic fields—whether from the welding current itself, nearby electrical gear, or stray magnetic sources—nudge the arc off course. And for Shielded Metal Arc Welding, SMAW, this effect is especially noticeable. The arc is generated between a consumable electrode and the workpiece, and the current path—along with the grounded clamp and the metal you’re trying to fuse—creates a magnetic environment that can steer the arc where you don’t want it to go.

What makes SMAW prone? It comes down to the setup and how the current travels. In SMAW, you’ve got a coated electrode that’s used as the flux carrier and the filler metal, with the current returning through the workpiece and a ground clamp. That flow of electricity in a relatively compact space, plus the metallic path of the electrode, is a magnet for arc deflection when a magnetic field is present. It’s one of those “physics at work in the shop” moments that feels almost theatrical—until you realize it’s a defect-prone blade of wind you need to calm.

The polarity part is a big piece of the puzzle. Many SMAW scenarios use direct current, and the polarity—whether the electrode is negative or positive—can intensify how sensitive the arc is to magnetic influences. In practice, you’ll hear about DC conditions amplifying arc blow, and you’ll see the arc behave differently if you swap polarity or switch to AC where that’s suitable for the electrode you’re using. In short: the magnetic field plus a certain current path plus DC polarity can turn a clean bead into a wavy line. And nobody wants that on a thick plate or a pipe weld.

How SMAW stacks up against TIG, SAW, and GMAW

If you’re thinking, “What about TIG, SAW, or GMAW?”—you’re right to compare. Each process has its quirks, which influence how magnetism plays with the arc.

• TIG welding (GTAW): Here you’re using a non-consumable tungsten electrode and shielding gas. The current path is a little more isolated from the workpiece’s grounding because the tungsten piece doesn’t burn away like SMAW’s electrode. The arc tends to be steadier under magnetic influences, so arc blow is less of a spectacle. Still, you’ll hear about arc wandering in TIG too, but it’s usually less dramatic and easier to control with technique and fixture design.

• Submerged arc welding (SAW): This one uses a granular flux that shields the arc from the atmosphere and helps stabilize the arc. Because the flux and electrode feed create a different shielding and current profile, arc blow effects are often dampened. You still need to manage magnetic fields around large joints, but the flux blanket does a lot of the heavy lifting in keeping the arc on track.

• Gas metal arc welding (GMAW): Also known as MIG welding, this process relies on a continuously fed wire and shielding gas. The wire feed and the way the arc forms with a moving electrode tend to provide more arc stability in many situations. While magnetic fields can still influence the arc, the combined effect of constant wire feed and gas shielding often mitigates dramatic arc blow compared to SMAW.

In practical terms, SMAW’s combination of an active electrode, a grounded setup, and often larger current pulses makes it more susceptible to the arc wandering when magnetic fields are present. That doesn’t mean you can’t weld with SMAW near magnets or near equipment that emits fields; it just means you’ll want to pay closer attention to grounding and current setup, and be prepared with fixes when the arc starts to drift.

Signs and fixes: reading the arc and steering it back

So how do you know arc blow is rearing its head, and what can you do to bring the arc back in line? Here are the cues and the moves that actually work in a workshop environment.

Signs you’re dealing with arc blow

• The bead runs off to one side or the arc seems to “wander” as you’re welding.

• Your heat texturing, bead shape, or penetration isn’t consistent along the seam.

• You notice more distortion on one side of the joint than you’d expect from heat input alone.

• The issue is more pronounced on thicker materials or long, straight runs where the magnetic field can build up.

Common scenarios that invite arc blow

• Thick plates or joint configurations where the current loops extend in ways that amplify magnetic effects.

• DC polarity setups that emphasize a strong current path through the electrode and workpiece.

• Ground clamps that are far from the weld zone or placed in a position that doesn’tcapture the return current cleanly.

• Nearby electrical devices, magnets, or even heavy machinery whose fields distort the arc.

Practical remedies you can try

• Reposition the ground clamp. Make the return path as direct as possible to reduce stray magnetic loops. A common tweak is moving the ground closer to the weld zone or using multiple ground clamps for large joints.

• Change the polarity if your electrode allows it. Switching from one polarity to the other (or choosing an electrode with a polarity that’s better suited to the job) can lessen arc blow effects.

• Reorient your weld path. Sometimes welding along a different axis or rotating the joint so the arc’s natural path aligns with the field helps. It’s not about forcing the arc; it’s about giving it a straight, predictable route.

• Consider flux considerations and shielding approach. In SMAW, the flux does its part, but you can also rely on technique—like maintaining a steady travel speed and a stable electrode angle—to reduce arc wander.

• Use a magnetic shield or distance from magnetic sources. If there’s a strong magnet nearby or a big motor, try to create some space or shield the arc area with non-magnetic barriers.

• Break long, straight runs into shorter passes. Shorter arcs can be easier to control and less prone to arc blow across the joint.

What this means for your day-to-day welding

Let’s translate this into something that feels practical. When you’re tackling SMAW on a thick plate or a pipe weld, think of arc blow as a diagnostic signal. If the arc starts to wander, you have a few simple levers you can pull: adjust the ground, tweak the polarity, and check your joint orientation. You don’t have to accept the arc as is. With a little systematic fiddling, you can bring it back to a clean, stable bead.

A few quick, tested tips you can actually use

• Keep the ground close and the path direct. The shorter the return path, the less room there is for stray magnetic fields to skew the arc.

• Know your electrode. Some electrodes tolerate polarity better than others. If you’re not getting the results you want, a quick electrode swap can fix a surprising amount of drift.

• Don’t overthink the setup. Arc blow is more common than you’d expect, but it’s also highly manageable with method and small adjustments.

• Practice on test coupons with variations. Try a few joints at different angles, with clamps in various positions. You’ll start to notice patterns about where arc blow likes to show up and how to head it off.

A little context, a lot of relevance

Welding isn’t just about melting metal; it’s about guiding energy in a way that makes strong, clean joints. Arc blow is a reminder that magnetic forces aren’t just abstract physics—they’re real stuff you fight with in the shop. The way SMAW handles current, grounding, and the electrode path makes arc blow more noticeable here, but the observation doesn’t stop there. It’s a chance to sharpen your instincts: where will the arc go when the room hums with electric noise or when that magnetic field nearby isn’t cooperating?

People new to welding are sometimes surprised by how much environment matters. You can be the same welder who creates flawless beads with no fuss, and then, in a moment, arc blow changes the game if you haven’t looked at the ground path, the polarity, or how you’re approaching the seam. That’s not a fail—it's a cue to adapt. And in the real world, adaptation is what separates a good welder from a great one.

A few words about the broader picture

This is where the analogy clicks for many. Think of arc blow as a weather system in the workshop. You can’t stop the gusts, but you can read the signs and place yourself and your tools in a way that keeps the wind from turning your arc into a zigzag. In SMAW, the arc is so intimately tied to the electrode and the return current that magnetic nudges become part of the story. TIG, SAW, and GMAW each carry their own weather patterns, but SMAW’s blend of current path and flux behavior makes arc blow a little more conspicuous and a lot more teachable.

If you’re just starting to notice arc blow, you’re not alone. It happens to the best but learning how to counter it is what builds confidence. As you gain experience, you’ll start predicting where the arc might wander and what you’ll do to steer it back. And yes, you’ll likely pick up a few little habits that save you time and a few headaches along the way.

In the end, arc blow isn’t something to fear. It’s a signal—a reminder that the weld isn’t just about melting metal. It’s about managing the invisible fields that ride along with your current, the grounding you’ve laid out, and the way you hold the electrode as you coax a solid bead across the joint. With that mindset, SMAW remains a dependable, capable process—one where you can control the arc, one pass at a time. And that, in the long run, is what good welding is all about.