456A Weld Quality Inspection, Testing & Occupational Safety 1 — Questions and Answers
Question 1: What is the primary difference between a 'destructive test' and a 'non-destructive test' (NDT) in weld inspection?
- Destructive tests destroy the test coupon/weld to measure properties; NDT examines the weld without destroying it, allowing the tested component to remain in service (Correct answer)
- Destructive tests are performed on production welds; NDT is only for procedure qualification
- NDT detects surface defects only; destructive tests detect internal defects
- Destructive testing is optional; NDT is always mandatory on production welds
Correct answer: Destructive tests destroy the test coupon/weld to measure properties; NDT examines the weld without destroying it, allowing the tested component to remain in service
Destructive tests (tensile, bend, impact, macro, hardness) provide quantitative data on mechanical properties but consume the test specimen. NDT (visual, RT, UT, MT, PT, ET) examines the weld without destroying it, allowing the production component to remain in service. Qualification testing uses both; production inspection relies on NDT.
Question 2: What does 'visual inspection' (VT) detect in welds and what tools are used per CSA W59?
- Surface discontinuities including cracks, undercut, overlap, surface porosity, crater fill, weld profile/size, and weld length; tools include weld gauges, magnifying lens, fillet gauges, and adequate lighting (Correct answer)
- Only weld size and geometry; no discontinuities can be detected visually
- Internal discontinuities such as lack of fusion and internal porosity
- Visual inspection is not an accepted inspection method under CSA W59
Correct answer: Surface discontinuities including cracks, undercut, overlap, surface porosity, crater fill, weld profile/size, and weld length; tools include weld gauges, magnifying lens, fillet gauges, and adequate lighting
Visual inspection is the most fundamental and first NDT method applied to all welds. Qualified visual inspection per CSA W59 detects: cracks, undercut, overlap, surface porosity, crater fill adequacy, weld reinforcement/profile, weld size (leg and throat), length, and location. Tools include calibrated weld gauges (HI-LO gauges, fillet weld gauges, pit gauges), magnifying glass (up to 10×), adequate lighting (minimum 500 lux), and mirrors for access.
Question 3: What is 'radiographic testing' (RT) of welds and what type of defects is it most sensitive to?
- X-ray or gamma-ray imaging of the weld; most sensitive to volumetric discontinuities — porosity, slag inclusions, burn-through, incomplete penetration (Correct answer)
- Ultrasonic vibration of the weld metal; most sensitive to planar defects
- Magnetic field application to detect surface-breaking cracks only
- Penetrant dye applied to the surface; reveals surface-breaking discontinuities
Correct answer: X-ray or gamma-ray imaging of the weld; most sensitive to volumetric discontinuities — porosity, slag inclusions, burn-through, incomplete penetration
Radiographic testing uses ionizing radiation (X-rays or Ir-192/Se-75 gamma sources) that passes through the weld and exposes film or a digital detector. Denser material absorbs more radiation; discontinuities show as darker areas on the radiograph. RT is most sensitive to volumetric defects (pores, inclusions) aligned with the radiation beam. It provides a permanent record (film) but requires radiation safety procedures under CNSC regulations in Canada.
Question 4: What is 'ultrasonic testing' (UT) and what type of weld defects is it best suited to detect compared to RT?
- Uses high-frequency sound waves; best suited to planar defects (cracks, LOF, LOP) that are poorly detected by RT due to orientation (Correct answer)
- Uses electromagnetic induction to detect surface defects only
- Uses visible light refraction to measure weld geometry from the surface
- Uses acoustic emission detection during weld solidification to predict internal defects
Correct answer: Uses high-frequency sound waves; best suited to planar defects (cracks, LOF, LOP) that are poorly detected by RT due to orientation
UT uses piezoelectric transducers to send high-frequency sound waves through the weld. Discontinuities reflect sound back to the transducer (pulse-echo method), indicating location, depth, and size. UT is superior to RT for planar defects (cracks, LOF, LOP) oriented perpendicular to the sound beam because RT cannot reliably detect narrow planar defects. Phased array UT (PAUT) provides enhanced visualization and is increasingly specified in Canadian pipeline and structural codes.
Question 5: What is 'magnetic particle testing' (MT) and on which base metals can it be used?
- Uses magnetic fields and iron particle indicators to reveal surface and near-surface discontinuities; can only be used on ferromagnetic materials (carbon steel, low-alloy steel) (Correct answer)
- Uses high-powered magnets to attract subsurface defects to the surface for visual inspection
- Can be used on all metals including austenitic stainless steel and aluminum
- Detects internal voids using magnetic resonance imaging technology
Correct answer: Uses magnetic fields and iron particle indicators to reveal surface and near-surface discontinuities; can only be used on ferromagnetic materials (carbon steel, low-alloy steel)
MT applies a magnetic field to the workpiece and then applies magnetic particles (dry powder or wet fluorescent solution). Leakage flux at surface or near-surface discontinuities attracts the particles, creating a visible indication. MT is limited to ferromagnetic materials (iron, nickel, cobalt-based). Austenitic stainless steel and aluminum are non-ferromagnetic and cannot be inspected by MT — PT (dye penetrant) is used instead.
Question 6: What is 'dye penetrant testing' (PT) and what is the correct sequence of steps?
- Apply penetrant → dwell → remove excess → apply developer → inspect → post-clean; detects surface-breaking discontinuities in any non-porous material (Correct answer)
- Apply developer → apply penetrant → inspect → remove; works on all metals and non-metals
- Apply penetrant permanently and inspect under UV light immediately; used for subsurface defects
- Apply magnetic developer → wait → read with ultraviolet lamp; used for ferromagnetic metals only
Correct answer: Apply penetrant → dwell → remove excess → apply developer → inspect → post-clean; detects surface-breaking discontinuities in any non-porous material
The correct PT sequence is: (1) pre-clean and dry the surface; (2) apply liquid penetrant; (3) allow dwell time (typically 5–20 min) for the penetrant to seep into discontinuities; (4) remove excess penetrant; (5) apply developer to draw penetrant back to the surface and amplify indication; (6) inspect under adequate light; (7) post-clean the surface. PT detects surface-breaking cracks, pores, and LOF on any non-porous material regardless of ferromagnetism.
456A Weld Quality Inspection, Testing & Occupational Safety 1
What is the primary difference between a 'destructive test' and a 'non-destructive test' (NDT) in weld inspection?