Quality Control, Inspection, and Testing
What this domain tests
Inspection questions cover visual examination, weld gauges, NDT method selection, code acceptance criteria, and documentation. You need to know what each method can and cannot find.
Visual and dimensional inspection
Visual examination is the most-used method: check fit-up, root condition, bead profile, spatter, arc strikes, undercut, and final size. Good lighting and a clean surface are prerequisites. Weld gauges include the fillet weld gauge for leg and throat, undercut gauge, V-WAC, hi-lo gauge, and reinforcement gauge. Dimensional checks use tape, calipers, squares, and templates, or a CMM and laser tracker for complex work.
NDT methods
- Penetrant testing (PT): surface-breaking defects only, any nonporous material, requires a clean surface and developer.
- Magnetic particle testing (MT): surface and near-surface defects in ferromagnetic steel; not for austenitic stainless or aluminum.
- Ultrasonic testing (UT): internal defects, laminations, and thickness; needs trained operators and reference blocks.
- Radiographic testing (RT): internal volumetric defects such as porosity and slag; radiation safety controls apply.
- Destructive tests: bend, tensile, macro etch, and hardness, usually for procedure qualification.
Code acceptance and documentation
CSA W59 sets acceptance limits for undercut, porosity, reinforcement, fillet size, and weld length. Fillet throat is 0.707 times the leg for a 45 degree fillet. Inspectors verify WPS compliance for amperage, voltage, preheat, interpass temperature, and cleaning between passes. Records include inspection reports, MTRs, welder qualification, nonconformance reports, and corrective actions. Instruments need current calibration.
Worked example
A drawing calls for a 6 mm fillet. The leg measures 5.2 mm and the throat 3.9 mm. Required throat for a 6 mm fillet is 0.707 x 6 = 4.2 mm. Both leg and throat are below requirement, so the weld is undersized. It is rejected and repaired by adding a pass per the WPS, then re-inspected.
Traps
- Expecting PT or MT to find internal porosity.
- Measuring leg and reporting it as throat.
- Inspecting PT or MT over paint or scale.
- Skipping preheat and interpass checks.
- Using an out-of-calibration gauge.
- Accepting a weld that meets size but shows undercut beyond code.