Laminar type flaws with major dimensions parallel to the rolled surface are best found using which type of contact testing method?

The best method for detecting laminar type flaws with major dimensions parallel to the rolled surface is straight beam testing. This testing method utilizes a straight ultrasonic beam that is directed perpendicularly to the material's surface. Since laminar flaws are oriented similarly to the surface, a straight beam is most effective in identifying these defects due to its ability to penetrate the material uniformly and reflect back any signals from discontinuities directly beneath it.

Straight beam testing allows for clear detection of flaws that may not be perpendicular to the surface, as it can acquire signals reflecting off the flaw from different angles through the material, enhancing the likelihood of returning discernible signals to the transducer. This is particularly important for laminar flaws that can exist parallel to the surface, as they will often create reflections that a straight beam can catch, leading to accurate assessments of the material's integrity.

In contrast, other methods such as angle beam testing or synthetic beam testing are less suited for detecting flat, parallel-oriented flaws due to their approaches and the angles at which they emit ultrasonic waves. Circular beam testing, which primarily uses focused beams that diverge, may not effectively provide the needed sensitivity for this specific flaw orientation. Thus, straight beam testing stands out as the most appropriate approach for this scenario.