In order to prevent such disadvantages, various solutions for localizing the weld seam have become established. Optical methods that use color marking of the longitudinal seams to detect their position are widely used. There are also camera-based systems that search for the "natural" weld seam.

Weld Seam Detection even without color

But what to do if color marking is not possible or the seam is no longer visible? This problem arises when the application requires specific post-weld treatment of the pipe, such as in the production of precision steel pipes. The cold redrawing used here changes the original surface appearance and prevents the use of paint. If the pipe is also subjected to normalizing annealing, the seam can become invisible on the outside.

This is where Roland Electronic's alternative processes come into play. These are the methods known from non-destructive material testing, such as eddy current, magnetic induction and magnetic flux leakage testing. All have the advantage that they work dry and without significant radiation exposure.

Crystalline changes in the weld seam structure used for testing

These processes utilize the crystalline change in the microstructure in the area of the weld seam. When ferromagnetic steels are welded, martensitic crystals form in the heat affected zone. As martensite hardly occurs in the unwelded structure, the weld seam can be detected via the martensite. The SND40 weld seam detector, which supports these alternative methods, demonstrates great process stability in practice.

Detection rates of 99.9% are achieved in the first pass for pipes on which only the weld seam has been scraped and the diameter calibrated after welding. The error rates for a single SND40 system are between 0 and 100 ppm.