1.) Purchase the 3 bottles . 

2.) Clean the weld with the cleaner from bottle one and a clean 
    cleaning cloth. 

3.) Spray the red coulor from bottle two and wait 5-30 minutes

4) Clean the weld with the cleaner from bottle one and a clean 
    cleaning cloth. 

5.) Spray the developer from bottle three and wait 5-30 Minuten 

6.) Crack going up to the surface are clear visible as red spots. 

The pictures showing step 3.) and 5.) no cracks on this weld. 

regards Carsten