A steel mill had a quality problem in the manufacture of cold-rolled steel for use in applications such as automobile hoods. Several hot-rolled coils were welded end-to-end to form a long continuous band. The band included the welds that were made to join the original coils together. Unfortunately, many of these welds were failing under tension, causing damage and extreme danger as the coils flailed about.A functional test was performed at the weld station to discover why these coils were failing. After removing the long ridge of previously molten metal, the weld was removed in a 12 in. strip of steel from the full width of the coil. This was done four times every 8-hour shift. (In the steel mill an 8-hour shift is called a "turn".) A 1-in. diameter tool steel ball was pressed down into the test piece until a half-in. high bulge was raised on the opposite side. A failed weld bulge was one where a crack appeared, with some portion of that crack running parallel to the direction of the weld. The rationale for this definition was that such a crack implied that the weld had less ductility than the parent metal.

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