After boiling down all the complex elements of this job, this is what it comes down to in the end: how does a welding inspector distinguish good welds from bad welds. It maybe seems like an oversimplification of what’s rarely a simple discipline, but that’s not the case, not at all. At the end of the day, especially in what’s essentially an exacting engineering application, the job really should be measured in blacks and whites.

A Black And White Engineering Discipline

Shying away from the shades of grey, a welding inspector’s job is to transform “maybes” and “could be’s” into certainties. Okay, enough with the colourful metaphors, how does a welding inspector distinguish a properly implemented weld joint from one that’s not up-to-par? Step number one in the inspection handbook suggests a visual examination. Going back one extra step, before the visual inspection, what kind of welding technique is this? What’s the equipment, and what are the expected results?

MIG Welding Analysis

This is Metal Inert Gas welding, which is viewed by many as the most easily mastered metal joining method available. Consumable fillers and electrodes are at work, and there’s an electric arc generating the heat. A good weld has no discontinuities or metal discolouration. A bad weld is documented as a series of seam discontinuities and/or cracks. There’s discolouration around the weld and the seam is too thin. To correct these issues, clean the weld area, adjust the weld voltage, and bring in a welder who can maintain the travel rate of the electrode arc.

A TIG Welding Troubleshooter

Operator expertise is mandatory when working with Tungsten Inert Gas welding gear. Because of that fact, it’s easier for things to go wrong. There’s less leeway between a “Good” weld and one that’s gone “Bad.” Moving in closer and lower, the bottom side of the weld has insufficient penetration. There’s also an erratic or poorly formed bead. Worse yet, due to some trapped shielding gas, the heat application zone is full of small holes. This is metal porosity, yet another sign of a bad weld.

Oxy-welding seams suffer from the same problems, with insufficient underside penetration topping the list off jointing gaffes. Then there are the obvious porosity and cracking issues, plus a whole series of possible seam discontinuities. Still, just because a weld doesn’t look like it’s in pristine condition, that doesn’t always earn it a failing grade. It’s the same thing with seemingly good welds. Visually, the joint might look good, but those good looks could be hiding a buried discontinuity. As a quality control mechanism, welding inspectors use non-destructive test instruments to check seemingly good welds. As a test of an outwardly bad weld, those same test instruments come to the rescue.

As a rule, solid surfaces are stronger than welded structures. Surely, weldments create strong frame joints, but they’ll fail before a solid structural element does; that’s just the unmitigated truth of the matter. For this reason, structural engineers focus on weld integrity issues when they’re analysing welded frameworks. With that fact in mind, the goal here is to examine the “glue” that couples these structural clusters in place.

Defining the Stress-Accumulating Weldment Zones

Looking at a weld, the fused metal breaks down into several different areas. There’s the weld root which sinks deep. Moving upwards and outwards, a V-shaped mass of filler material swells from a newly applied butt weld. The weld toe outlines the joint. The whole mass is discoloured but recently cleaned. This is where the heat affected zone once super-heated the weld pool. As a static joint, the weld satisfies all but a few requirements. Visually, the dome-like weld might exhibit a few minor flaws, but as long as those surface defects don’t indicate a larger problem, the joint receives a passing grade. Crack propagation dyes and test instrument can, of course, be called in at the weld inspector’s discretion. More worryingly, when working on a welded structure, there are a number of cyclical stress factors to address.

Crack Production and Propagation Mechanisms

A welding inspector is preparing to analyse a welded structure. There are long rows and columns of fused joints supporting hundreds of steel beams and plates. How can this one individual ever hope to tackle a project of this size? No worries, there are tools and methods aplenty. There are multi-axial stresses being placed on the welds. To handle all of these multidirectional forces, which each come with accompanying high or low amplitude loading stress field, there are computational analysis systems that have been created to assess the fatigue limits of weld structures. They use early detection mechanisms and tabulated datasets to predict how a structure’s stress fields will affect the toe or root of a weld. Inputted into a number-crunching computer, the stress analysis info predicts internalized fatigue conditions so that a stress limiter mechanism can be introduced to offset the cyclical stress.

To correct or even entirely neutralize the loading stressors, they need to be identified. Using finite element modelling, the likely loading culprits are tracked down and offset. One approach requires an increase in weld toe and root size, but do know that this solution doesn’t remove the source problem. As a more effective answer, fatigue production should be removed before it can cause weld cracks. Framework alterations and/or material physical changes (courtesy of a malleability-oriented heat treatment strategy) can effectively neutralize cyclical structural stressors.