What Material Factors Should Be Tested When Doing Welding Inspection?

21 March 2018

Encumbered by numerous tools and specialized instruments, weld inspectors strike out in search of jointing flaws. They’re also armed with less weighty assets. These are the applied science qualifications that inform their senses. Besides weld discontinuity identification, though, all weld inspectors are charged with another important duty. Using stereo microscopes and other optically enhanced instruments, every potential weld-compromising material factor is assessed. Here’s what happens next.

Interpreting the Impact of Thermal Bias 

The welding inspector examines a newly ticketed weld junction. A special microscope, one capable of examining the macro scale, views the material. We’re looking for thermal expansion, an uneven swelling that distorts the joint. Different alloys react differently when heat is applied, so this expansion and contraction effects requires monitoring. Thermal conductivity, another heat-related material factor, further aggravates the issue. Certainly, the problem emerges when two different metals require fusing, but it also appears when alloyed and heat treated metals possess contrasting physical properties. Carbon-heavy metals illustrate this point. All things considered, that common alloying element is a particularly efficient heat absorber.

Swayed by Filler Metal Impurities 

The weld zone melts then cools uniformly. Even the HAZ (Heat-Affected Zone) is cooperating today; it’s dissipating the thermal energy but not changing mechanically or physically under the heat load. The filler, however, is introducing impurities. Always source a superior filler, a product that closely matches the weld material. After saying that, even the finest fillers can act as a key material factor. In this case, it’s the micro scale that impacts the melt site. For example, a standard V-groove butt joint cuts a notch in a hot-rolled steel panel. So far, so good, but here comes the weld operation. The filler is a near solid, a melt aid that’s equipped with a fine microstructure. By contrast, the V-notch is formed from a recrystallized, hot-worked alloy that has undergone several property-altering processes in a heat treatment furnace. Documented before the operation started, the welding inspection checks to make sure the filler metal matches that base alloy.

Things are rarely that simple. If they were, a look at the documentation would be enough. No, even if the material factors are satisfied in writing, a weld inspector utilizes a more penetrating assessment methodology. Equipped with microscopes and non-destructive testing techniques, thermal coefficients are examined. Alloy mismatches and material conductivity considerations are mapped out and reported. Even that HAZ site, the area around the weld, is materially examined so that the entirety of the joint zone can be gauged as a successfully concluded piece of work. Weld grain size, expansion and contraction microcracks, and filler impurities, all of these material factors fall under the domain of a welding inspection.

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