## 4 Applications
### Applications in the Steel Industry
#### 4.2.2 Heavy Plate Testing  
Heavy plate with a slab thickness of up to 400 mm or more is produced in nearly all unalloyed and alloyed steel grades today. The diverse range of properties, e.g., yield strengths from 200 to more than 1100 N/mm\({}^{2}\) ensures the precise suitability for use in bridges, high rise buildings, offshore platforms, ship building, line pipes, pressure vessels, heavy-duty machines, and much more. In order to reduce the constructive thicknesses and, with it, the self-weight of a construction, higher-strength steel grades are increasingly requested, while the weldability and the cold toughness must still be acceptable. For the production of such steel grades, modern manufacturing processes, such as water/air quenching and tempering, accelerated cooling, normalizing, and thermo-mechanical rolling are applied. The customer asks for geometrical and mechanical properties, which are uniform across product length and width, especially for these high-value grades. Consequently, high demands are made on the determination and documentation of product quality. Comprehensive dimensional, shape, and surface inspections already take place within the production flow directly on the plate. On the other hand, it is still necessary to extract tests coupons from the edges of the un-trimmed plate in order to determine the mechanical properties. Tensile and toughness tests are performed according to the codes and delivery from highly qualified and certified personnel and they cannot be integrated into online closed loop control with direct feedback. Costs in the range of several thousands of Euros per year arise in a mid-sized heavy plate plant from coupon scrap alone. For these reasons, heavy plate producers are eager to replace the mechanical testing of coupons by nondestructive technology, allowing for these tests to be transferred from the laboratories of quality assurance to the shop floor. In a first project, a 3 MA system was integrated into a trolley, allowing for 3 MA tests to be performed on plates moving on the roller conveyor line in the steel plant. Figure 15 shows this device. A brushing device was integrated into the trolley in order to the remove scale that otherwise represents a strong disturbing influence. Calibration was done on coupons that were taken from the running production. It was apparent that the best results could be achieved if individual calibration functions were used for each steel grade and each plate thickness. In this case, the RMSE was in the range of 4 HB (Brinell hardness) for hardness determination, 10 MPa for Rm, and 20 MPa for Rp0.2. The main objective of a second project was to avoid pseudo-scrap in heavy plate by the precise detection of the so-called cold ends in the mother plate after rolling [65]. This is shown in Figure 16. Cold ends are developing due to altered cooling conditions and at the plate ends. The cold ends are characterized by impaired mechanical properties (Rm and Rp0.2). Therefore, they have to be removed  
Figure 15: Remote application of the 3 MA system in the roller conveyor line of a steel plant: (**a**) 3 MA inspection trolley and (**b**) remote control desk. in order to assure a plate that fulfills the quality requirements over the entire length. For this purpose, large sections--usually much larger than the cold ends--are cut off. Due to these safety margins, pseudo-scrap is produced, i.e., material, which still fulfills the requirements on material conformity, is unnecessarily removed and scrapped. In order to avoid this pseudo-scrap, the extension of the cold ends has to be precisely detected. This can be accomplished by 3 MA. The plates that were investigated in this project were steel grades showing a pronounced anisotropy of material properties due to a rolling texture. Therefore, it turned out to be useful to combine the measuring information from 3 MA with measuring parameters that are derived from the time-of-flight (TOF) measurements of ultrasound (US) waves.