In the world of structural fabrication, structural steel welding plays a vital role in the integrity, durability, and safety of everything from bridges and buildings to industrial frameworks. Structural steel welding is a complex process that goes far beyond simply joining pieces of metal—it requires precision, planning, the right equipment, and, above all, the correct welding process for the environment in which the work is performed.
For today’s structural steel fabricators, every job comes with a unique set of challenges: tight bidding competition, stringent code compliance, rigorous inspection standards, and the need for effective training. However, the cornerstone of any successful structural welding project lies in selecting the most appropriate welding process and filler metal. This decision can determine the project's overall efficiency, cost-effectiveness, and quality, whether the work is performed in a controlled indoor shop environment or out in the unpredictable field.
Understanding the Environment: Field vs. Shop in Structural Steel Welding
The setting of a project significantly impacts the welding process for structural steel fabrication. Environmental variables such as wind, accessibility, equipment portability, and surface cleanliness determine the effectiveness and feasibility of certain welding methods.
When welding structural steel outdoors, wind becomes a major concern, particularly because it disrupts shielding gases critical to some welding processes. Therefore, welding methods used in the field must be resilient, portable, and less dependent on gas shielding.
In contrast, indoor shop environments offer controlled conditions that allow fabricators to adopt higher-efficiency processes with fewer environmental concerns. This opens up a broader range of structural welding techniques that may not be suitable for field use.
Welding Processes for Field-Based Structural Fabrication
Field welding often utilizes Shielded Metal Arc Welding (SMAW), commonly known as stick welding, and Self-Shielded Flux-Cored Arc Welding (FCAW-S). These processes are ideal due to their portability and ability to perform well under outdoor conditions.
Stick welding is familiar, simple, and doesn’t require external shielding gas, making it a go-to for operators who frequently relocate during a job. However, it is also a slower process due to frequent electrode changeovers—each stick typically lasts only about 12 inches of weld. For jobs requiring large or multi-pass welds at a fixed position, switching to FCAW-S can significantly enhance productivity.
FCAW-S uses a continuously fed wire and delivers a much higher deposition rate than stick welding. If most of the welding during the job is stationary, FCAW-S is a superior choice. But in highly mobile welding tasks, stick welding’s simplicity may still offer better efficiency.
Choosing between the two may also involve re-qualifying welding procedures. While this involves upfront effort and time, it is often offset by the long-term gains in welding productivity and cost savings.
A hybrid approach is also feasible—utilizing stick welding for minimal weld areas and switching to FCAW-S in heavy weld zones. This maximizes both mobility and productivity in the same structural steel fabrication project.
Additional Field Considerations:
Hydrogen levels: Most American Welding Society (AWS) 7018 stick electrodes, which are the most widely used, have low diffusible hydrogen levels (4ml per 100g or H4 is common). The FCAW-S wires are H8 (8ml per 100g) or higher; H4 is not available.
Power sources: FCAW-S should be used with a constant voltage (CV) power source. Depending on the classification of the wire, it may require DCEN or DCEP polarity. DCEN is more common but not used for all FCAW-S wires. In many cases, an operator may already have a multi-process machine capable of these settings. If not, a CV-capable power source needs to be purchased.
Training: FCAW-S wires have distinct characteristics and operating requirements depending on the AWS classification (type of wire), including specific voltage and stick-out (electrode extension) settings. These wires require the use of specific gun angles and travel speeds to achieve the best weld quality, too. Training for welding operators without FCAW experience is important.
Welding Processes for Shop-Based Structural Steel Applications
Shop environments open up more welding process options due to stable conditions. Here, Gas-Shielded Flux-Cored Arc Welding (FCAW-G), Gas Metal Arc Welding (GMAW/MIG), and Submerged Arc Welding (SAW) are the dominant processes in structural fabrication.
FCAW-G is a favorite for structural welding in shops due to its versatility and forgiving nature. These wires handle a wide parameter range and are less sensitive to operator error. They can even weld through surface contaminants such as mill scale—commonly present in structural steel. However, FCAW-G produces slag that requires cleanup between passes, potentially reducing overall productivity.
MIG welding, particularly with solid or metal-cored wire, offers a cleaner alternative. MIG eliminates slag and the associated post-weld activities like grinding and chipping, significantly reducing non-value-added labor. However, MIG isn’t as suitable for out-of-position welding and struggles with dirty base metals compared to FCAW-G.
Metal-cored wire provides an excellent middle ground. These wires are more tolerant to operator inconsistencies, have higher deoxidizer levels for welding through mill scale, and support a broader range of parameters—making them highly effective for structural fabrication under shop conditions.
Submerged Arc Welding (SAW)is the ultimate productivity booster in shop settings, especially for long, continuous welds on beams and structural sections. Though it requires significant capital investment, SAW’s benefits include high deposition rates and reduced heat input—cutting down on the need for post-weld straightening and increasing travel speeds.
A Productivity Example with SAW
Let’s consider a scenario: using a 1/8" SAW solid wire at 100 wire feed speed (WFS) and 30 volts results in 650 amps and a travel speed of 22 inches per minute (IPM) to achieve a weld size "X." Now, replacing it with a 1/8" metal-cored wire at the same amperage but increasing WFS to 150 allows a travel speed of 27.5 IPM. That’s a 25% increase in speed and a 25% reduction in heat input—a major advantage in structural steel welding applications where efficiency translates directly into cost savings.
Labor Costs: The Hidden Driver in Structural Welding Efficiency
In structural fabrication, labor is often the most significant cost. Even minor improvements in weld cycle time can produce enormous savings over the course of a project. Whether it’s through faster deposition, reduced cleanup, or minimized rework, selecting the most appropriate structural welding method is critical.
Conclusion: Optimizing the Welding of Structural Steel
Whether in the field or the shop, structural steel welding demands a balanced approach to quality, productivity, and cost. Every structural fabrication project benefits from a critical assessment of whether the current welding process is truly the most efficient. Factors like weld volume, operator skill, environment, and equipment capability must all align to make the right choice.
By taking the time to understand each welding process—from stick welding and FCAW-S in the field to MIG, FCAW-G, and SAW in the shop—fabricators can optimize their operations. The welding process for structural steel fabrication isn’t one-size-fits-all, but when well-matched to the job, it becomes a cornerstone of success in the structural welding industry.
Related articles:
1. AWS D1.2: Aluminum Structural Welding Standard Guide
2. Ship Structural Welding International & Industry Standards
3. Common Welding Methods for Steel Structures Welding
4. A Basic Guide To Structural Welding
5. How to Weld Stainless Steel: Tips and Tricks
