A beam getting a full penetration groove weld inside a warm, dry shop is a totally different job than patching a busted support column in a freezing warehouse in February. Same word, welding. Totally different problem. A structural welding is not just about one thing. It’s a toolbox. Stick, flux core, MIG, TIG, each one works differently, and grabbing the wrong tool doesn’t just slow you down. It can leave you with a weld that fails inspection, or worse, one that doesn’t hold the load it’s supposed to hold.
This guide walks through the four big structural welding methods, the weld shapes they create, and the real world stuff, steel thickness, wind, cold, code rules, that decides which one a welder actually grabs off the truck.
What Is Structural Welding?
Structural welding is a types of welding that holds up buildings, bridges, and platforms, the stuff that can’t just fall over. It joins beams, columns, plates, and braces so the finished weld carries the load an engineer already calculated on paper. It usually follows an approved welding procedure specification, called a WPS, and it often gets inspected before anyone covers it up.
Patching a fence post or fixing a broken gate hinge? Nobody’s checking that against a stamped engineering drawing. Structural welds are different. They carry consequences.
A warehouse expansion going up in Brampton and a bridge repair out near Sudbury both count as structural welding. But the joint shapes, the steel thickness, and the code rules attached to each look nothing alike. That’s exactly why welders don’t just pick one process and run with it forever.
What Are the Main Types of Structural Welding?
Four processes cover almost every structural steel job out there: stick welding (SMAW), flux cored arc welding (FCAW), MIG welding (GMAW), and TIG welding (GTAW). Each one protects the melted metal, the weld pool, in a different way. That difference decides where each process actually gets used on a site or in a shop.
1. SMAW / Stick Welding
Stick welding runs off an electrode coated in flux. The arc melts the rod and the base steel together while the flux coating burns and forms a crusty slag layer on top. That slag shields the hot metal from air while it cools.
You’ll see stick welding on field connections, bracing, angle iron, repairs on old steel that’s sat outside for twenty years. Picture a crew fixing a bent loading dock canopy support in an unheated building in January. Wind rips through the open bay doors. Rust coats the steel. Stick shrugs all of that off. A gas shielded process would just get blown apart before the arc even settled.
Good stuff about stick: cheap gear, handles wind and light rain, doesn’t care about rust or mill scale, barely any setup. Not so good: it’s slow, you chip slag between passes, and weld quality rides almost entirely on the welder’s hand. Crews reach for stick on remote sites, outdoor repairs, and anywhere a gas shield just won’t survive.
FCAW / Flux Cored Arc Welding
Flux cored welding feeds a hollow wire packed with flux instead of a solid rod. Self shielded FCAW makes its own gas cloud from the flux burning inside the wire. Gas shielded FCAW adds an outside gas bottle too, kind of like MIG’s tougher cousin.
This one shows up constantly on big steel jobs, multi story frames, heavy plate work, industrial structures going up fast. Steel erectors bolting together the upper floors of a windy commercial tower usually run self shielded FCAW, because there’s no gas cloud for the wind to steal.
It lays down metal fast and bites deep into thick plate, way quicker than stick. The tradeoff? More smoke, more spatter to clean off, and self shielded FCAW has limits on position and thickness that the project’s WPS spells out in black and white.
GMAW / MIG Welding
MIG welding pushes a solid wire through the gun nonstop while a bottle of gas, usually a blend of argon and CO2, protects the puddle from air. Inside a fab shop building connection plates, stair stringers, HSS tube frames, or handrail brackets, MIG keeps the line moving. It’s fast, and the weld looks clean with barely any spatter to grind off later.
Take it outside, though, and the story flips. Wind scatters that gas cloud in seconds, leaving the puddle wide open to contamination. That’s the whole reason MIG welding mostly stays indoors or under a shelter on site.
GTAW / TIG Welding
TIG welding uses a tungsten electrode to strike the arc, and a filler rod gets fed in by hand when the joint needs it. The welder controls heat and puddle size almost like painting with a fine brush.
On structural jobs, TIG welding handles thin gauge material, stainless architectural pieces, and root passes on connections where looks and precision actually matter, an entrance canopy at a building lobby, say. It’s rarely the pick for big structural members. The deposition rate is just too slow for thick plate or high volume work.
Common Structural Weld Types: Fillet, Groove, CJP, and PJP
Here’s where people mix things up. The welding process, how the arc works, isn’t the same as the weld type, what shape the finished joint takes. FCAW describes the machine and the shielding. A fillet weld describes the shape sitting there once you’re done. A welder can lay down a fillet weld using stick, MIG, or flux core, whatever the WPS calls for on that print.
Fillet welds join two pieces at roughly a right angle, forming a little triangle where they meet. You’ll spot these on clip angles, gusset plates, beam to column brackets, everywhere really. Groove welds sit inside a prepped gap between two members, common on butt joints and moment connections carrying serious load in a straight line.
Complete Joint Penetration welds, CJP for short, fuse all the way through the joint. Engineers call for these where the connection needs full strength, a column splice on a high rise, for example. Partial joint penetration, PJP, only fuses part way through, used when full strength isn’t needed, like some stiffener plate attachments.
Plug and slot welds fill a drilled hole or a cut slot to join overlapping plates. That trick shows up a lot in retrofit work, bolting a reinforcing plate over an old connection during a repair job.
Structural Welding Methods Compared
| Process | Typical Applications | Production Speed | Field Suitability | Weld Control | Advantages | Limitations |
|---|---|---|---|---|---|---|
| SMAW (Stick) | Field erection, repairs, bracing | Slow to moderate | Excellent (wind, rain, dirty steel) | Operator-dependent | Portable, tolerant of poor conditions | Slower, slag cleanup, skill-sensitive |
| FCAW (self-shielded) | Steel erection, heavy structural fabrication | Fast | Good outdoors | Moderate to good | High deposition, strong penetration | More fumes/spatter, position limits |
| FCAW (gas-shielded) | Shop fabrication, thick plate | Fast | Limited outdoors | Good | Fast, good penetration | Needs gas shield protection from wind |
| GMAW (MIG) | Shop fabrication, connection plates, HSS | Fast | Poor outdoors | Good, clean welds | High productivity, low spatter | Shielding gas disrupted by wind |
| GTAW (TIG) | Thin material, architectural steel, root passes | Slow | Limited | Excellent precision | Clean, precise, controlled heat | Slow, impractical for thick or high-volume work |
How Do You Choose the Right Structural Welding Process for Your Project?
Picking a process isn’t about grabbing whatever machine sits closest to the joint. It comes down to the approved WPS for that specific connection. Steel thickness, joint shape, welding position, shop or field, all of it feeds into what the WPS actually calls for.
Say a manufacturing plant is adding on, and the crew needs outdoor column splices during a windy November erection push. Self shielded FCAW usually wins over MIG here, because MIG’s gas shield just can’t survive that wind. Meanwhile, that same plant’s shop built base plates might run on MIG all day, since the shop walls protect the gas and speed matters more than portability indoors.
What to Consider Before Choosing a Structural Welding Process
- Steel type and thickness at the joint
- Joint configuration: fillet, groove, CJP, or PJP
- Required welding position (flat, horizontal, vertical, overhead)
- Shop conditions versus field or outdoor conditions
- Access and clearance around the joint
- Production volume and project timeline
- Approved WPS for the specific connection
- Applicable codes and project specs, including CSA W47.1 and engineering drawings
Structural Welding Codes, Procedures, and Qualified Welders in Canada
A WPS writes down the exact recipe, process, amperage, joint prep, filler metal, position, that produced a tested weld everyone agreed was good enough. Welders have to pass their own qualification test for the specific process and position they’re using. Passing one test doesn’t hand you a blank check for every process or joint type out there.
In Canada, fabricators and erectors usually carry certification under CSA W47.1, which covers the company’s quality program and welding operations as a whole. That’s a company level certification, separate from an individual welder’s ticket. A welding shop can hold W47.1 and still make every welder pass a test for the process, position, and material on a given job.
Ontario field jobs add another wrinkle. Wind on an open steel frame messes with gas shielded processes way more than it messes with stick or self shielded FCAW. Cold weather bumps up preheat requirements on thicker plate. A commercial job in Toronto, an industrial retrofit in Kitchener, and a bridge repair out on a rural highway each bring their own weather, access, and inspection headaches. Project specs and engineering requirements drive the decision. Not whatever a crew feels like doing that morning.
Conclusion
Four processes, stick, flux core, MIG, TIG. Four different personalities. None of them fits every joint on every job, and that’s kind of the whole point of having options. Steel thickness, joint design, shop or field conditions, and the approved welding procedure decide what belongs on a connection. Not convenience. Not habit.
Structural welds carry weight that a fence repair never will. That’s why any change or repair to structural steel needs an engineer’s sign off and a qualified welder working from a project specific WPS. Before you scope out a repair, a retrofit, or a brand new connection, talk to a qualified welding services provider in your area about the process, the procedure, and the inspection steps your project actually needs
Frequently Asked Questions
What are the main types of structural welding?
Stick (SMAW), flux cored (FCAW), MIG (GMAW), and TIG (GTAW). Each one shields the weld differently, so each one fits different steel thicknesses, positions, and shop-versus-field setups.
What type of welding is best for structural steel?
There’s no single winner. The right pick depends on the project’s approved WPS, the steel thickness, the joint design, and whether the crew is working in a shop or out in the wind.
Is stick welding suitable for structural steel?
Yes. Stick welding shows up constantly on structural steel, especially field erection, repairs, and outdoor connections where wind or dirty steel would wreck a gas shielded process.
Is MIG welding used for structural welding?
It sure is, mostly in shops and fabrication settings, connection plates, HSS members, stair or handrail parts, anywhere the shielding gas stays protected from wind.
What is FCAW used for in structural welding?
Heavy structural erection and fabrication. Its high deposition rate speeds up big jobs, and the self shielded version handles outdoor work without needing an external gas bottle at all.
