Visual Testing “The Foundation of NDT”
Updated: May 12, 2021
Visual Testing is the most underrated method of NDT Testing. If you think about it, Visual Testing is the foundation for all of NDT. It does not matter what method you are utilizing whether it is Radiographic Testing (RT), Ultrasonic Testing (UT), Magnetic Particle Testing (MT), Penetrant Testing (PT), etc., you inevitably use Visual Testing.
How did you come to this conclusion some may ask? Well, it is quite simple. Let's say that you are to perform an Ultrasonic Examination on a weld. What is the first thing that you look at? Exactly, the weld. What you just did was a Visual Examination. If there is no weld, do you need to waste time performing an Ultrasonic Examination? The answer is no. Let's say you can visually see porosity at the surface that exceeds the accept/reject criterion, do you need to proceed? Again, the answer is no.
Visual testing has been around since the 1800’s and first got implemented into specifications in the early 1900’s starting with ASME’s Boiler & Pressure Vessel Code, First Edition. Since I have been in NDT (2006) I have seen the wording change from “Certified Individual” to “Qualified Individual”. In my opinion this downplays the importance of a good Visual Technician. Recommended Practice SNT-TC-1A lays out the steps needed to become a Qualified & Certified Level I, II, & III in Visual Testing. Example: 24 hours of Classroom Training. Again, in my opinion these 24 hours are a critical part of even being a “Qualified Individual”. Most industries see a “Qualified Individual” as someone who can read a tape measure, calipers, and micrometers but, is that really all that is needed to become a “Qualified Individual”? The answer should obviously be NO. Knowing the limitations of a testing method is critical in ensuring that all inspections are carried out thoroughly, with quality being at the forefront. More than likely a “Qualified Individual” does not know the minimum angle for optimal viewing of discontinuities to cast a shadow off a light. They most likely have no idea what a borescope is, and what happens to your eyes when you enter an area that has a significant change in light intensity. (If you are looking to get Qualified & Certified in other methods like MT or PT this is extremely useful.)
Now let us discuss the difference between “Qualified” & “Certified”. Certified by definition is “Written testimony of Qualification” and when used in conjunction with SNT-TC-1A your ASNT Level III VT should review that you have completed 24 hours of classroom training for Level II, have the OJT hours of 210 in VT specifically with a total of 400 in NDT, and taken all exams. Where “Qualified” is written becomes a gray area. I have seen some industries that simply ask the Technician to perform the Examination and if they could they were deemed “Qualified”. This should be laid out in your companies “Written Practice”.
Since some of the fundamentals you learn in Visual Testing carry over into other methods and that is why I believe that Visual Testing is the basis for ALL NDT Testing methods and that those who are deemed “Qualified” should seriously look at what it takes to become “Certified”.