One of the first requirements for the performance of nondestructive testing (NDT) arose when visual inspections were mandated following fatalities from a boiler explosion in the late 1800s.
Around this same time, X-rays were discovered and as their uses in NDT evolved, so did the development of the liquid penetrant method (railroads using oil & whiting at first) in the 1920s followed by initial developments of eddy current and magnetic particle testing in the 1930s and ultrasonics in the early 1940s.