In the construction of large, above-ground welded steel storage tanks, achieving a perfect, leak-tight weld at the critical junction between the tank floor and the shell is paramount. This foundational weld is subject to significant stress from the weight of the tank contents and environmental forces.
To ensure the highest quality weld that meets stringent industry standards for integrity and durability, construction teams rely on specialized aids, one of the most important being the flux belt.
This temporary, yet crucial, component is integral to the semi-automatic welding process used for this critical joint, ensuring a flawless fusion that forms the primary seal of the storage tank.
Facilitating the Laydown Weld
The flux belt is essential for the “laydown” or fillet weld that joins the vertical steel shell plates to the horizontal steel bottom plates.
Due to the position of this corner joint—at ground level and essentially horizontal—it presents unique challenges for standard welding processes. The flux belt acts as a dam or containment system.
When the welding machine applies flux-cored wire and granular flux over the joint, the belt physically holds the molten flux and metal in place, preventing the molten puddle from running out or sagging away from the joint. This ensures a consistent, uniform weld bead profile.
Optimizing Submerged Arc Welding (SAW)
The superior quality achieved at the tank bottom-to-shell joint is typically accomplished using the Submerged Arc Welding (SAW) process. The flux belt is designed to work in tandem with semi-automatic SAW equipment.
This process uses a continuous feed of welding wire and a blanket of granular flux that completely covers the arc. By containing this blanket of flux, the flux belt creates the necessary deep pool of molten material.
This allows for deeper penetration and a cleaner weld than other methods, a crucial factor for the longevity and structural integrity of the tank.
Ensuring Consistent Weld Penetration
One of the most critical roles of the flux belt is to guarantee consistent weld penetration. Without it, gravity would pull the molten weld pool downward, resulting in an inconsistent cross-section, potential voids, and insufficient fusion to the bottom plate.
By holding the weld pool volume in place, the flux belt helps maintain the heat and pressure required for the molten metal to fully fuse with both the bottom plate and the shell plate. This deep and consistent penetration is what prevents leaks and gives the tank base its long-term structural reliability.
Protecting the Weld from Contamination
During the welding process, environmental factors can compromise the integrity of the weld. Air currents, moisture, and ground contamination can introduce impurities or cause rapid cooling, leading to defects like porosity or cracking.
The granular flux, contained by the belt, acts as a shield to prevent atmospheric exposure. This protective mechanism ensures that the molten metal remains pure and cools at a controlled rate, significantly reducing the likelihood of weld flaws and subsequent costly repairs.
Streamlining Post-Weld Inspection
A properly applied flux belt contributes to a smooth, uniform surface on the completed weld bead. This consistency is not just aesthetic; it makes the post-weld inspection process much simpler and more reliable.
Inspectors often use methods like Magnetic Particle Testing (MPT) or Ultrasonic Testing (UT) to verify weld quality.
A smooth, even weld profile, achieved with the assistance of the flux belt, ensures that inspection probes and materials can be applied evenly, allowing for the accurate detection of any subsurface flaws.
