456A Weld Quality Inspection, Testing & Occupational Safety

Question 1

What is the primary difference between a 'destructive test' and a 'non-destructive test' (NDT) in weld inspection?

Accepted 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

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

X-ray or gamma-ray imaging of the weld; most sensitive to volumetric discontinuities — porosity, slag inclusions, burn-through, incomplete penetration

Answer

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?

Accepted Answer

Uses high-frequency sound waves; best suited to planar defects (cracks, LOF, LOP) that are poorly detected by RT due to orientation

Answer

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?

Accepted 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)

Answer

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.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A Weld Quality Inspection, Testing & Occupational Safety