I assume, that only this experience out of a lot of possible other examples results in the question from above: "What kind of testing system will be most efficient for a certain type of tubes?"

Before the development of a nondestructive tube inspection system, the main tasks and specific features of the material under test as well as the official regulation and standards must be clarified.

Precision tubes like boiler tubes, ball - bearing tubes, heat exchanger tubes, tubes for the chemical industry, high pressure tubes etc. are very much different from API tubes and other hot rolled tubes for construction.

Some precision tubes are made from stainless steel, like austenite, titanium or Zircaloy. Mostly the surface of precision tubes is very smooth or polished and without dust and oxide scale. The production length can be 30 m and more. The straightness is very good and the other tolerances of OD, OV are very small. The size of the lots, or the number of tubes in a lot are sometimes also very small; that means the production and the inspection facilities must be flexible for quick changes of the tube dimensions. The inspection system must also be flexible to fulfill the various regulations like smaller or larger reference flaws, e. g. 50µm ... 0.1 mm depth, 0.75 mm ... 15 mm length; reference flaws of various orientations like longitudinal, transverse, seldom oblique flaws; lamination inspection; and last but not least a high precision dimension measurement is required for WT, OD, ID, OV, WV, and EXC.

The surface of hot rolled tubes and API tubes is black and covered with dust and scale. The straightness as well as the other tolerances of OD, OV are also worse. Sometimes tubes have upset ends. The inspection system must also be flexible to fulfill the various regulations like smaller or larger reference flaws e. g. 0.1 mm. ... 5% WT depth, 12 mm ... 50 mm length; reference flaws of mainly longitudinal orientation, but also transverse and oblique flaws may be required; lamination inspection; and last but not least a 100% WT measurement, but also OD, ID, OV, WV, and EXC.