Guía Técnica de Soldadura por Arco Sumergido Industrial para Vigas de Gran Peralte

In the current landscape of manufacturing infrastructure in Mexico, the expansion of industrial buildings for the automotive, aerospace, and heavy logistics sectors in regions such as El Bajío, Saltillo, Torreón, and Piedras Negras has triggered a surge in demand for buildings with clear spans exceeding 30 or 40 meters. To support these spans and the dynamic loads of heavy-duty overhead cranes, commercial hot-rolled steel sections (IR or IPR sections) are insufficient in depth and load capacity. The structural engineering solution is the design of built-up girders made of three plates (variable section or deep girders), whose fabrication requires the application of industrial submerged arc welding to ensure structural integrity and economic viability of the project.

As plant engineers and infrastructure project managers, we know that the bottleneck in a structural steel fabrication shop is not plasma plate cutting, but rather the deposition rate and radiographic quality of the fillet welds between the web and the flanges of these girders. Attempting to fabricate these full or partial penetration joints using manual or semi-automatic processes not only drives up labor costs but also exponentially increases the risk of thermal distortions and rejections due to Non-Destructive Testing (NDT).

This technical article details the critical variables, applicable regulations in Mexico, and best workshop practices for the implementation of the SAW welding process in the fabrication of deep girders.

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Table of Contents

• 1. Introduction to Submerged Arc Welding (SAW) in Heavy Industry
• 2. What are Deep Girders and Why Do They Require the SAW Process?
• 3. Technical Principles of Industrial Submerged Arc Welding: Electrode, Flux, and Arc
• 4. Advantages and Disadvantages of SAW Welding in the Fabrication of Three-Plate Girders
• 5. Key Regulations and Specifications in Mexico: AWS D1.1 and IMCA
• 6. Critical Control Parameters in Industrial Submerged Arc Welding
• 7. Technical Comparison: SAW vs. GMAW and FCAW for Steel Structures
• 8. Quality Control and Non-Destructive Testing (NDT) in Welded Girders
• 9. Common Errors in the Mexican Industry When Welding Girders with SAW
• 10. Real Case: Fabrication of Deep Girders for an Industrial Building in Saltillo, Coahuila
• 11. Professional Checklist for Automatic Welding of Girders with SAW
• 12. Optimization of Workshop Engineering for Large-Scale Projects in Mexico
• Frequently Asked Questions
• Conclusion
• Sources and References

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1. Introduction to Submerged Arc Welding (SAW) in Heavy Industry

The Submerged Arc Welding process (SAW) is an automatic or semi-automatic method that has become the backbone of heavy-duty steel structure fabrication. Unlike open arc processes such as SMAW (shielded metal arc welding) or GMAW (MIG/MAG), Submerged Arc Weldingoperates under a highly efficient granular flux layer. industrial submerged arc welding SAW

This configuration completely eliminates the emission of direct ultraviolet and infrared radiation in the work area, drastically reduces metallic fumes in the workshop—which facilitates compliance with NOM-027-STPS-2008 (Safety and Hygiene Conditions in Welding and Cutting Work)—and allows for extremely high current densities without the risk of arc instability or spatter. In the context of heavy manufacturing in Mexico, where delivery times for industrial buildings are extremely aggressive, the SAW process's ability to operate with 100% duty cycles represents a critical competitive advantage for any steel fabrication shop.

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2. What are Deep Girders and Why Do They Require the SAW Process?

In structural engineering, a deep girder (or three-plate built-up beam) is a flexural element whose ratio between the clear span and the total height (depth) requires a custom design. Generally, they are fabricated by joining three independent steel plates: a thin but deep vertical web, and two more robust horizontal flanges (top and bottom). The standard material specified in the structural plans of modern industrial buildings in Mexico is ASTM A992 steel or ASTM A572 Grade 50, which offer a minimum yield strength of 50,000 psi (345 MPa).

   [ Patín Superior ]  <-- Placa de gran espesor (p. ej., 1" a 2")
          | |
          | |          <-- Alma (Placa delgada de gran peralte, p. ej., 1/2" a 5/4")
          | |
   [ Patín Inferior ]  <-- Placa de gran espesor

Industrial welding SAW steel girder fabrication becomes mandatory due to the following factors:

• Dissimilar plate thicknesses: Joining a 1/2" (12.7 mm) web with 1.5" (38.1 mm) flanges requires controlled but high-penetration heat input to prevent lack of fusion at the fillet root.
• Extreme lengths: Girders for industrial building spans typically measure between 12 and 30 meters long. Performing these continuous welds manually would cause constant stops to change electrodes, generating start and stop points (starts and stops) which are areas prone to discontinuities such as porosity or slag inclusions.
• Distortion control: The concentrated heat and high travel speed of submerged arc welding for beams minimize the heat-affected zone (HAZ) compared to slow manual processes, drastically reducing flange warping and web angular distortion.

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3. Technical Principles of Industrial Submerged Arc Welding: Electrode, Flux, and Arc

The success of industrial submerged arc welding lies in its physical simplicity and chemical sophistication. The process uses a continuous electrode of solid or tubular wire that is mechanically fed through a welding torch. The electric arc is established between this electrode and the ASTM A992 steel workpiece.

                  [Alambre de Electrodo Continuo]
                                |
                                v
                       .::::::::::::::::.  <-- Tolva de Fundente (Flux)
                      .:::[ FUNDENTE ]:::.
                     .::::::::::::::::::::.
  [Escoria Solidificada]  /  (Arco Oculto) \
       =============     /       |          \
      [Metal de Aporte] <--------+-----------> [Baño de Fusión]
       =============
  -------------------------------------------------------------
                       [Metal Base / Viga]

The role of submerged arc flux

Industrial submerged arc flux (flux) is a granulated mineral compound (containing silicon, manganese, titanium, calcium oxides, among others) that is gravity-fed in front of the electrode. When melted by the arc temperature (exceeding 6,000 °C), the flux performs three critical functions:

1. Atmospheric protection: Completely isolates the molten filler metal from oxygen and nitrogen in the air, eliminating the need for external shielding gases.
2. Deoxidation and alloying: Chemically reacts with the weld pool to purify the steel, remove impurities, and, in some cases, add alloying elements to improve the mechanical properties of the deposit.
3. Slag formation: Upon cooling, it forms a vitreous slag layer over the weld bead that slows down the cooling rate, preventing the formation of brittle structures (martensite) in the HAZ and giving the bead an excellent aesthetic appearance with a flat or slightly concave fillet profile.

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4. Advantages and Disadvantages of SAW Welding in the Fabrication of Three-Plate Girders

As in any manufacturing process, technology selection must respond to a cost-benefit analysis. Below, the pros and cons of SAW welding process in the structural steel fabrication shop are detailed:

Advantages

• Unmatched deposition rates: Allows depositing up to 15 kg/h of filler metal with a single wire, and more than 30 kg/h in double wire systems (tandem arc).
• Deep penetration: Reduces the need for deep bevels on web plates, allowing full penetration fillet welds with minimal joint preparations, which saves setup time and reduces weld consumption.
• Consistent metallurgical quality: Being an automatic beam weldingprocess, variations associated with operator pulse and fatigue are eliminated. Welds are uniform, spatter-free, and have ultrasonic rejection rates below 1%.
• Safer work environment: Since there is no visible open arc, the risk of eye burns (electric arc) for surrounding personnel in the workshop is reduced, optimizing the workspace in accordance with NOM-025-STPS-2008 (Lighting conditions in workplaces).

Disadvantages

• Limited to flat and horizontal positions: Due to the granular nature of the flux, the SAW process is restricted to welding positions 1F, 2F, and 1G. It requires the use of positioners or beam rotators in the workshop.
• High initial investment cost: SAW welding equipment (1000A power sources, welding tractors, or gantry-type systems) has a significantly higher cost than conventional MIG/FCAW machines.
• Requires precision assembly: The process does not tolerate severe variations in the root opening (root opening). If the fit-up (fit-up) of the plates has excessive gaps, the flux and molten metal will leak through ("spill-through"), ruining the joint.

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Table 1: Typical deposition parameters based on beam web thickness

Web Thickness (in / mm)	Wire Diameter (in / mm)	Current (Amperes)	Voltage (Volts)	Travel Speed (cm/min)	Deposition Rate (kg/h)
3/8" / 9.5 mm	1/8" / 3.2 mm	450 - 500 A	28 - 30 V	50 - 65	5.5 - 7.0
1/2" / 12.7 mm	5/32" / 4.0 mm	550 - 650 A	30 - 32 V	45 - 55	8.0 - 10.5
3/4" / 19.0 mm	3/16" / 4.