"B" Scan is a method of verifying material lost over a large percentage of surface area. This technology has been around for a long time. It introduces ultrasonic waves perpendicular to the surface of the material and the returning signal reveals the material thickness. By traversing the transducer over the surface of the material, the thinnest cross-section can be located. Water or other material can be used as the couplant that connects the transducer to the material being examined.
Coupled with a printer, these cross-sections can be displayed into an easy to read visual image. Imagine taking a cross-section of wall thickness and turning it on edge. This would allow you to look at the thickness of the part at the cut surfaces. Whereas normal thickness readings only display the thickness under the transducer, "B" scan reveals the full line of thickness over the full scan. This is an excellent method of inspection for lamination scans, corrosion underneath tank floors and at any time a more thorough examination is required on a vessel or pipe wall.