Students measuring weld profiles on test sample
METHOD
Visual testing is an NDT method that is applied at the beginning, during, and at end of fabrication of the part. This can include welding, casting, and forging. In case of welding, visual testing is done from weld preparation, application of the welding procedure specification (WPS), all the way through to the final weld. A VT inspector must have knowledge of the fabrication steps to the final product. Visual testing can be direct or remote. Direct VT is done with the human eye within 12 to 24 inches of the part. Remote is done using instruments such as videoscopes.
There are many other areas where visual testing is performed. Visual testing for service induced damage can include corrosion, pumps, valves etc.
Visual testing is also done on consumer goods and automobiles. This is done by machine vision.
VT ACCEPTANCE CRITERIA AND CODES
Not all discontinuities found by visual testing are rejectable. One of the most important steps in visual testing is to determine whether the discontinuity is acceptable or a reject. This requires thorough knowledge of the acceptance criteria in the applicable code.
EQUIPMENT
Magnifying glass, flash light, measurement gauges. Gauges include Cam guage, fillet, V-wac etc.
APPLICATIONS
Visual testing has a range of applications that include inspection of welding, castings, forgings, composites, coatings etc. Welding inspection includes checking for bevel preparation, proper fit-up prior to welding, misalignment, final weld profile, weld discontinuities such as slag, porosity, undercut, cracks etc. Composite inspection looks for delaminations, matrix cracking, impact damage, blistering.
INDUSTRY CODES
- AWS D1.1 for structural weld inspections.
- ASME VIII, Div 1 for pressure vessels
- ASME codes – various
TRAINING
- VT Level II
- Duration – 24 hours (includes Level I)
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