Reducing Welding Errors in Metal Construction

Numerous welding techniques exist: shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and flux core arc welding (FCAW). Welding uses diverse tools: welding clamps, torches, power sources, consumable electrodes and specific safety equipment. To ensure structural building integrity and durability, and prevent structural failure, the welding process must be completed without errors. Welding errors produce defects, flaws or imperfections that compromise the intended use of a weldment. While not a complete list, here are some common welding errors and how to avoid them.

Poor Preparation

Poor preparation can cause welding errors. Dirt, paint, rust, grease and other contaminants must be removed from the metal before it is welded. Brushing the metal’s surface eliminates oxides. Oxide buildup in the weld area can cause inconsistencies by preventing contact at the weld joint. Aluminum materials need to be cleaned more thoroughly than other types of metal. Failure to correctly clean the material before welding will result in a contaminated and weakened weld. Obviously, to prevent welding-related injuries, the correct safety equipment (safety glasses, hearing protection, safety boots, welding helmet) needs to be put on before welding.

Cracks

Cracks are a serious weld defect because they can cause an entire welded structure to fail. Cracks can be classified as traverse if they are at a 90-degree angle or across the weld, or longitudinal if they are parallel to the weld. A crater crack has a star-like shape and is usually present where the weld bead terminates. Cracks can be external or internal and are planar. Cracks can occur because of the contraction of the solidifying metal and the growth of grains.

Before welding, fully grind out any cracks on the weld metals that are not immediately visible to the naked eye. If cracks are not fully ground out, metal will continue to crack after the weld has been made. To avoid cracks, grind, clean, fill and/or deburr metal edges so pieces can easily fit together. Preheating deters cracking, since it slows down the cooling rate after welding. The type and thickness of the material being welded determines preheat and interpass temperature.

Crater cracks are a common welding defect that frequently occur when welding aluminum. They form at the end of the weld bead. If they are not repaired, they could create stress points, which can cause cracking in the weld. Correctly terminating the weld bead can prevent craters from occurring. To repair a crater that does not have cracks in the weld bead, fill in the crater after starting an arc strike beyond the crater and work back over the crater.

Spatter

During GMAW welding, spatter occurs when droplets of molten particles are produced near the welding arc. It happens when welding currents are too high, there is incorrect polarity or if there is insufficient gas shielding. These droplets can cool and solidify along the sides of the weld bead, stick to the base material and surrounding metallic material, and even fly and fall onto the work area.

This is primarily an aesthetic issue but spatter that accumulates in the nozzle can detach and damage weld beads. To prevent this, reduce the welding current and arc length to better control the metal transfer. Use the correct polarity and check the shielding gas type and flow rate. Clean the gas nozzle and increase the torch-to-plate angle. Check for bad ground connections and loose or damaged cables, which can lead to excessive spatter. Damaged cables can also cause drops in voltage and lower heat input, resulting in inconsistent weld quality.

Porosity

Porosity happens when nitrogen, oxygen and hydrogen gas bubbles accumulate in the molten weld pool and are released on solidification to become trapped in the weld metal. It can occur internally and also on the surface. These hollow bubbles compromise weld strength. To prevent this, check the gas flow rate (too low or high can create issues) and use higher quality gases that have higher purity in their composition. Move the torch slow enough to keep a molten puddle, allowing the gas to bubble out. Check the welding torch for leaks, and ensure the metal is dry and clean. Keep the amperage from getting too high. Clean the gas nozzle of the welding device and ensure the torch-to-plate angle is not too large or small. Avoid a long arc.

A Shielding Gas Mixture

“For the GMAW process, [welders] may be actually using a shielding gas mixture,” explains Steve Snyder, AWS-SCWI, CWS, CWE, ASNT NDT Level III, ASQ-CQA, CMQOE, staff welding specialist at American Welding Society, Miami. “For example, 75% Argon and 25% CO2 exhibits a considerably lower heat input, and generally operates in what is known and referred to as the GMAW-short circuit mode. [This is] associated with lower amperage, voltage and heat inputs—intended primarily for applications for light-gauge and sheet steel, applications, usually under 3/16-inch to 0.312-inch applications—resulting in lower weld metal fusion and penetration on the thicker steel base material.

“This [is] compared to using an optional shielding gas mixture, with at least 80% Argon to be capable of the GMAW process commonly referred to as the globular or the preferred GMAW-spray transfer mode of weld metal. Use of non-spray arc mode in GMAW, can routinely lead to both lack of weld metal fusion and/or penetration into the base metal, and other non-desirable weld discontinuities. This could also promote potential premature weld failures.”

Training and Codes

Snyder claims a common root cause of welding errors is, “not having properly trained, qualified and certified welding personnel and the proper welding procedure specifications in place. [This] will certainly also lead to poor quality and eventually more than likely a welding quality non-conformance issue, or worse case being a weld failure. I have found over the years, several erection sites lacking in the actual personnel qualified and certified, as well as not having the welding procedure specifications in place when and if welding is required in the field. Any field welding or shop not clearly identified or specified on the contract approved drawings can result in errors.”

To mitigate and avoid welding defects, understand the building code requirements like the International Building Code and those found in the American Institute of Steel Construction. “Most, if not all these codes, standards or typical structural steel specifications will reference to AWS welding standards or codes for welding conformance,” Snyder says. “[Also,] I always suggest a contract review, i.e., review your PO from your customer, the specifications and note any gaps which you may not be able to adhere to or do not understand clearly.”