Welding for the Strong: A Guide to Structural Welding Methods

What type of Welding is Used for Structural Steel

Structural steel refers to a variety of steel products that are used in construction projects. It is typically made from alloy steel and is valued for its high strength and durability. Structural steel is used to build large structures like bridges, buildings, stadiums, and more. It allows constructors to create structures that are incredibly strong and able to withstand extreme forces.

Some of the main uses and advantages of structural welding include:

• High strength-to-weight ratio — Structural steel has a high strength-to-weight ratio, which allows buildings to reach great heights without becoming too heavy. This makes it ideal for skyscrapers and large structures.
• Durability — Structural steel has a very long lifespan and is resistant to weathering and corrosion. Steel structures can last for decades with proper maintenance.
• Formability — Structural steel can be bent, welded, cut, and formed into a variety of shapes. This flexibility allows for innovative and unique building designs.
• Cost-effectiveness — Using structural steel in construction is often more affordable compared to other building materials. It requires less labor to erect and can speed up construction schedules.
• Fire resistance — When properly insulated, structural steel performs well in building fires. The material itself does not burn or enable fire spread.

With its unique combination of strength, durability, work ability, and cost-efficiency, structural steel has become an indispensable construction material used for large and small building projects worldwide. Understanding the types of welding used for structural steel is key for constructors.

Types of Welding Used

Structural steel fabrication involves joining together steel components to create buildings, bridges, and other structures. Several welding processes are commonly used to join structural steel, each with their own advantages and applications. The most popular welding methods include:

• Arc Welding — Arc welding applies heat generated by an electric arc to melt and fuse metal components. Shielded metal arc welding and gas metal arc welding are two common forms. They allow for fast fabrication and high deposition rates on thicker materials.
• Gas Metal Arc Welding (GMAW) — Also known as MIG welding. Uses a continuous solid wire electrode fed through a welding gun, along with an inert shielding gas. Allows higher welding speeds than SMAW. Useful for welding thicker and multiple pass joints.
• Flux-Cored Arc Welding (FCAW) — Similar to GMAW but uses a tubular wire filled with flux instead of a solid wire. Does not require external shielding gas. Provides higher deposition rates than GMAW and good penetration on thicker sections.
• Submerged Arc Welding (SAW) — Uses an automatically fed consumable electrode and granular flux. The arc is submerged under the flux to provide a protective blanket. Allows very high deposition rates for thick joints. Commonly used for welding heavier steel plates.
• Electroslag Welding — A highly productive vertical welding process used to make full penetration single pass welds on thick materials. The arc is initially struck under flux, then maintained by the resistance of the molten slag which melts the filler metal and base materials.
• Stud Welding — A specialized process where studs are welded onto steel structures to facilitate connections. Often applied in structural steel construction to allow connections between beam webs and steel decking.

Arc Welding

Arc welding is one of the most common types of welding used for structural steel. It uses an electric arc to melt and join metals. An electric current is passed between an electrode and the metals being welded, creating an arc of high temperature that melts the metals at the point where they join. As the electrode is moved along the joint, the molten metals cool and solidify, forming a strong weld.

The electrode, which carries the electric current, can either be a consumable rod that melts into the weld puddle, or a non-consumable tungsten rod that only creates the arc. Consumable electrodes are often coated with flux, a material that helps prevent oxidation and impurities. The most common arc welding processes are shielded metal arc welding (SMAW), gas metal arc welding (GMAW), flux-cored arc welding (FCAW), and submerged arc welding (SAW).

Arc welding is versatile, inexpensive and can be done manually or by automation. It’s suitable for all types of metals and ideal for structural applications because it can make high-strength and high-integrity welds. The concentration of heat from the electric arc allows for deep weld penetration and efficient fusion of the base metals. Overall, arc welding is one of the best techniques for welding structural steel components.

Gas Metal Arc Welding

Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is an arc welding process that uses a continuous solid wire electrode. The wire electrode and the weld pool are protected from atmospheric contamination by being “shrouded” by an inert or semi-inert gas, typically a mix of argon and carbon dioxide.

GMAW requires a constant voltage, direct current power source. The electrode wire is continuously fed through a welding gun and into the weld pool, joining the two base materials together. A constant, preset voltage maintains the arc between the tip of the wire and the base material being welded. The parameters of current and voltage can be adjusted to modify the amount of heat input during welding. The wire feed speed can also be changed to control the speed of the welding process.

The major advantages of GMAW include its high welding speed, high quality welds, ease of automation, and minimal post-weld clean up required. It’s commonly used for welding thicker sections of steel in applications such as in structural construction and fabrication.

The main limitations are that it can only be used in relatively flat or horizontal welding positions, and has limitations welding through dirty or rusty materials. Overall, GMAW is an extremely versatile and useful welding process for a wide range of materials and applications.

Flux-Cored Arc Welding

Flux-cored arc welding (FCAW) is a semi-automatic or automatic arc welding process that uses a continuous wire electrode. The electrode wire is hollow and filled with flux that protects the weld from contamination.

FCAW requires similar equipment to MIG welding, but uses wire that contains materials in its core that supply the shielding gas and slag on its own. This makes it suitable for welding in outdoor environments where it’s tricky to supply external shielding gas.

The flux-cored wire contains alloying metals like chromium, nickel, molybdenum, manganese, and silicon. As the wire melts, the flux covering disintegrates, generating a shielding gas around the weld. This prevents spatter and protects the weld from oxidation and contamination.

FCAW is a high deposition rate process used on materials like mild steel, low alloy steel, stainless steel, nickel alloys, and some aluminum alloys. The flux makes it possible to weld on dirty or rusty materials.

The process can be used in all positions and generates uniform, high-quality welds. FCAW is commonly used in structural steel construction and in the shipbuilding industry. It’s also used for welding large structures, machinery, railroad tracks, and girders.

Submerged Arc Welding

Submerged arc welding (SAW) is a common arc welding process ideal for welding thick materials. It involves an arc between a bare metal electrode and the weld pool. The arc is shielded by flux, which is a granular compound placed on the metal being welded. As the weld is laid, the flux melts and forms a protective blanket that prevents spatter and contamination of the weld.

The flux is continuously fed into the welding process, staying ahead of the arc. It covers the entire welding area rather than just the arc, as in some other welding methods. The blanket of flux helps the welding process by:

- Stabilizing the arc
- Providing shielding from atmospheric contamination
- Shaping the weld as it solidifies
- Removing impurities from the weld metal

Submerged arc welding is known for its high deposition rates and ability to weld thick materials in a single pass. The flux and electrode wire are fed automatically, so it is heavily used for automated and mechanized welding. It requires a constant voltage or constant current power source. The American Welding Society classifies SAW as one of the major arc welding processes.

Some key benefits of submerged arc welding include:

- High welding speeds and metal deposition rates
- Ability to weld thick materials up to about 50 mm in a single pass
- Minimal operator skill required compared to manual welding
- Good mechanical properties and quality welds
- Low risk of porosity or cracking

Submerged arc welding excels at welding thicker carbon and low alloy steels. It is commonly used to make welds for structural steel in heavy fabrication, pressure vessels, shipbuilding, and similar industries. The high deposition rates make it economical for high volume welding.

Electroslag Welding

Electroslag welding is an arc welding process that utilizes an electric arc to preheat and melt a filler metal electrode. The molten electrode then flows across the joint seam, forming a weld pool that joins the two pieces of metal together.

This welding process uses a granular flux to generate the heat required to melt the electrode and base metals. An electric current passes through the flux, which causes it to liquefy into a conductive slag pool. The high resistance of the flux causes it to heat up rapidly to temperatures over 5,000°F.

The molten slag and metal provide a conductive path for the current between the electrode and workpieces. As the electrode melts, droplets detach and fall through the slag pool, becoming the filler metal for the weld joint. The workpieces never melt during this process.

Electroslag welding is commonly used for thick materials over 1 inch thick, such as structural steel components. The slow solidification of the large weld pool makes it ideal for materials that are susceptible to cracking. It provides deep penetration welds and can join multiple workpieces in a single pass.

This specialized welding technique requires heavy-duty electrical power supplies to generate the high amperages needed. The equipment is more complex and costly than standard arc welding setups. However, for thick materials, it provides quality welds with good mechanical properties in all welding positions.

Stud Welding

Stud welding is a specialized type of welding that is commonly used in the construction industry for structural steel applications. This process uses a stud gun to quickly attach studs or fasteners to steel structures.

The stud gun uses an electric arc to melt the end of the stud and the surface of the steel base material. This creates a molten pool that fuses the materials together when it solidifies. The fastener becomes permanently joined to the steel structure.

Stud welding provides a number of advantages for structural steel construction:

• It is very fast, allowing workers to attach hundreds of studs per hour. This improves productivity on the job site.
• The solid weld joint creates a strong connection. Studs welded to structural steel can securely fasten sheeting, frames, and other components.
• Portability — Stud welding guns allow fastening studs in any position, even overhead or vertical. The guns are lightweight for easy maneuvering.
• Welders can access confined spaces since the gun is compact and has a long reach. This allows stud welding in tight spots.
• It works on rusty or painted steel surfaces. The welding arc penetrates coatings to make a clean weld.

Stud welding does require skilled operators to position the gun correctly and avoid poor welds. When performed properly, it is an excellent choice for permanently fastening studs and fixtures to structural steel in buildings, bridges, and other infrastructure. The speed and strength of stud welds make it a popular choice for steel construction.

Laser Beam Welding

Laser beam welding is a type of welding that uses a focused laser beam as a concentrated heat source to join materials. The laser beam melts and fuses the materials together by heating a very small area to extremely high temperatures.

Laser beam welding has some key advantages over other welding processes:

• It provides a high power density, allowing for deep weld penetration and high welding speeds. The laser can weld thicker materials than typical welding methods.
• It has a very small heat-affected zone, minimizing distortion and damage to the base material.
• Lasers can be focused and directed with precision, enabling welds in hard-to-reach areas and complex joint configurations.
• No filler material is required for most laser beam welding applications. The base metals are simply melted and fused together.
• It is a clean process with no sparks, fumes or material waste.

Laser beam welding requires joint surfaces to be in close contact. The process is commonly used to weld stainless steel, aluminum, titanium, and other metals in industries like aerospace, automotive, medical devices and electronics. It is a versatile option for joining dissimilar metals.

The equipment required is more complex than traditional arc welding. Lasers must also be enclosed for safety. But for many applications, laser beam welding improves quality and capabilities over other welding techniques. It is an important technology for high-performance structural steel construction.

Final thought

Structural steel requires strong, high-quality welds to meet building codes and ensure safety. The most common welding processes used are arc welding, gas metal arc welding, flux-cored arc welding, submerged arc welding, electroslag welding, stud welding, and laser beam welding.

The choice depends on the specific project, types of steel, joint design, quality needs, production rate, and cost. Proper welding method is critical for structural integrity in steel construction. Expert welders can work on specific welding types depending on welding requirement.