Practical experience with square pulse thermography for finding inclusions in stainless steel

For inline applications the so called square pulse technique (SPT) is easy to automate and needs less power from the source, because energy can be brought into the probe for a longer time span. Further its strength (in relation to flash pulse technique) is to find voids deeper below the surface. Therefore all of the calculations and practical verifications in this paper will be done only with square pulse. This work sets the focus on differences between practical experience and theoretical calculations. All practical square pulse tests were made with a specimen of stainless steel with an inclusion of air. For calculations we will use algebraic solutions of the heat diffusion equation as well as finite differences method. To show the differences to the practical values, their disscussion is based on diagrams with both: practical and calculated values of temperature progress. Additionally some experiences of how to avoid measurement faults will be explained.