Examination method
Visual testing (VT)
Direct examination of the weld and surrounding material with the eye, aided by light, gauges, and optical instruments, and the only method applied before, during, and after welding.
How it works
The inspector examines the joint under adequate illumination, at a suitable distance and angle, using magnification and mirrors where access or detail demands it. Light striking a surface irregularity casts a shadow or reflects differently, and it is that contrast the eye reads. Low-angle lighting is deliberately used because it exaggerates surface relief.
Measurement turns observation into data. Fillet gauges, reinforcement gauges, undercut gauges, hi-lo gauges, and simple straightedges convert what the eye sees into dimensions that can be compared against requirements and recorded. Without measurement the examination is only an opinion about appearance.
The method's real power lies in timing. Before welding it verifies material, fit-up, cleanliness, and preparation. During welding it confirms preheat, interpass cleaning, bead sequence, and that each root and fill pass is sound while access still exists. After welding it assesses profile, size, and surface condition on the finished joint.
Strengths
- Lowest cost per weld of any examination method, with no consumables and minimal equipment
- Applies at every stage, so problems are caught while they are still cheap to correct
- Immediate results with no processing time, film, or interpretation delay
- Detects the fit-up, preparation, and procedure failures that cause internal defects later
Limitations
- Finds only surface conditions, so it says nothing about the interior of the weld
- Depends heavily on the inspector's training, attention, eyesight, and lighting conditions
- Access can be impossible on the far side of pipe or inside closed assemblies without remote aids
- Surface coatings, heavy scale, or spatter can hide the very conditions being looked for
Key variables
- Illumination
- Both intensity and direction matter; low-angle light throws shadows across surface relief and reveals cracks a flat wash of light hides.
- Viewing distance and angle
- The eye resolves less detail as distance grows and as the viewing angle flattens, so both are controlled rather than left to chance.
- Surface condition
- Cleanliness governs what can be seen. Examination of a slag-covered or heavily scaled weld is not an examination at all.
- Gauges and aids
- Fillet, reinforcement, undercut, and hi-lo gauges plus mirrors and borescopes turn access and judgement problems into measurements.
- Timing
- Whether the examination happens before, during, or after welding decides what is even accessible to look at.
What an inspector watches for
- Confirm adequate lighting and viewing distance, since a properly lit surface reveals conditions that are invisible under poor light
- Clean the surface before judging it, because slag, spatter, and scale hide cracks and undercut
- Use gauges rather than estimating, as fillet size and reinforcement height are routinely misjudged by eye
- Record what was examined and when, because the in-process observations are the part nobody can reconstruct afterwards