The weld seam detection in tubes is a difficult subject because of the many variables involved:

• the welding method

• the type of material used: regular mild steel, highly alloyed steel, magnetic or nonmagnetic stainless steel and, of course, all types of  high-strength steels being used primarily in the automotive industry

• the wall thickness of the tube, e.g. magnetic flux leakage methods are limited by the depths of their wall thickness penetration

• the type of treatment that the welded tube received, e.g. annealing or coating

That is the reason that Roland has two systems available:
the older tried and proven model SND 30 which functions exclusively according to the magnetic flux leakage methods and the new PC-based SND40 system which, in addition, functions also with various types of eddy current probes and a combination of magnetic flux leakage and eddy current.