Large-diameter tubes with wall thicknesses above 25 mm are produced from shaped heavy plate with a submerged arc welded longitudinal seam. The large wall thicknesses (and therefore the large inspection volume), different tubetypes and the common inspection specifications usually require a large number of probes to detect the different defect types (longitudinal defects, transverse defects, laminations, tandem inspection, clad pipe inspection, pipe end inspection).

Coupling via water jets and laser-based tracking of the weld seam are important features of the testing system. As with the spiral tube test, two test systems are usually used: The first test system detects welding defects at an early stage of production. These errors are then repaired. The second testing unit works after the expander and serves as the final inspection of the tube.