AWS Welding Defects & Quality Control 1 — Questions and Answers

Question 1: Which NDE method is best suited for detecting surface and near-surface cracks in ferromagnetic welds?

Radiographic testing (RT)
Magnetic particle testing (MT) (Correct answer)
Ultrasonic testing (UT)
Visual testing (VT)

Correct answer: Magnetic particle testing (MT)

Magnetic particle testing (MT) is the most sensitive and practical method for detecting surface and near-surface (up to ~1/4 inch) cracks in ferromagnetic materials like carbon and low-alloy steel welds.

MT works by magnetizing the ferromagnetic test piece. At surface or near-surface discontinuities (cracks, lack of fusion), magnetic field lines leak out, creating flux leakage fields that attract magnetic particles (dry powder or wet fluorescent suspension). These particles form visible indications at the discontinuity. MT is limited to ferromagnetic materials (cannot be used on austenitic stainless steel or aluminum). Techniques: yoke method (portable, AC or DC), prod method (higher sensitivity, arc burn risk), or coil/head shot (for geometry-specific shapes). Fluorescent MT under UV light increases sensitivity.

Question 2: Liquid penetrant testing (PT) is applicable to:

Any material — ferromagnetic and non-ferromagnetic alike (Correct answer)
Ferromagnetic materials only
High-temperature components only
Subsurface defects only

Correct answer: Any material — ferromagnetic and non-ferromagnetic alike

Liquid penetrant testing works on any non-porous material regardless of magnetic properties — it detects surface-open discontinuities in metals, ceramics, and plastics alike.

PT relies on capillary action to draw a penetrant liquid into surface-breaking discontinuities. After a dwell time, excess penetrant is removed and developer applied, which draws the trapped penetrant back out to form visible indications. PT works on ferromagnetic steel, austenitic stainless, aluminum, titanium, nickel alloys, ceramics, and plastics — any non-porous, cleanable surface. It cannot detect subsurface defects. Per AWS and ASME codes, PT is used on austenitic stainless and aluminum where MT is ineffective. It is sensitive to surface cracks, cold laps, and laps.

Question 3: Lack of fusion (LOF) in a groove weld is best detected by:

Visual testing alone
Radiographic testing (RT)
Ultrasonic testing (UT) (Correct answer)
Magnetic particle testing (MT)

Correct answer: Ultrasonic testing (UT)

Ultrasonic testing (UT) is most effective for detecting lack of fusion because planar defects (LOF, cracks) perpendicular to the ultrasonic beam reflect strong signals, while RT often misses planar defects oriented parallel to the X-ray beam.

Lack of fusion is a planar (flat) discontinuity — the unfused interface between weld metal and base metal. Radiographic testing projects X-rays through the weld; planar defects oriented nearly parallel to the beam are difficult to detect (minimal density change across the thin defect). UT sends sound waves through the weld; planar defects perpendicular to the beam create strong reflections (high indication amplitude). AWS D1.1 Clause 6.11 specifies UT procedures for structural welds; UT is often preferred for thick-section CJP groove welds where LOF and lamellar tearing are concerns. TOFD and phased-array UT are increasingly used for code compliance.

Question 4: Lamellar tearing in welded joints occurs:

In the weld metal along the centerline due to solidification shrinkage
In the base metal below the HAZ in low-ductility, through-thickness directions of rolled plate (Correct answer)
At the weld face due to excessive restraint
Between weld passes due to slag inclusions

Correct answer: In the base metal below the HAZ in low-ductility, through-thickness directions of rolled plate

Lamellar tearing occurs in the base metal below and parallel to the fusion line in rolled plate with low through-thickness ductility, caused by through-thickness contraction stresses during weld cooling.

Lamellar tearing occurs in rolled plates (especially thicker sections) where non-metallic inclusions (sulfides, silicates) are elongated parallel to the rolling direction. Through-thickness tensile stresses from weld shrinkage initiate cracks that link through the inclusion bands, creating a staircase-pattern fracture parallel to the plate surface, below the HAZ. Susceptible configurations: T-joints with full penetration welds, corner joints. Prevention: use Z-direction tested plate (ASTM A770 — through-thickness tensile test), use low-restraint joint design, butter the plate surface before welding, or use low-hydrogen electrodes and procedures to minimize residual stress.

Question 5: What does 'Charpy V-notch' (CVN) impact testing measure in weld procedure qualification?

The maximum hardness of the weld HAZ
The fracture toughness (energy absorbed during fracture) at specified temperatures (Correct answer)
The fatigue life of the weld joint
The diffusible hydrogen content of the weld deposit

Correct answer: The fracture toughness (energy absorbed during fracture) at specified temperatures

CVN testing measures the energy (in ft-lbs or Joules) absorbed by a notched specimen during fracture impact, characterizing the weld metal's fracture toughness and ductile-to-brittle transition temperature.

Charpy V-notch testing per ASTM E23 strikes a notched beam specimen with a pendulum hammer, measuring absorbed energy. For welding procedure qualification: CVN tests confirm weld metal and HAZ toughness at service temperature (e.g., -20°F for bridge steel per AASHTO, -40°F for offshore per AWS D1.1 Annex I). Minimum energy requirements (e.g., 20 ft-lbs at -20°F) are specified in codes and project specifications. Factors affecting CVN results: heat input (higher = coarser grain = lower toughness), interpass temperature, electrode hydrogen, PWHT, and base metal chemistry.

Question 6: A weld that fails the guided bend test during procedure qualification typically indicates:

The electrode was the wrong size
Lack of fusion, excessive porosity, or cracking in the weld joint (Correct answer)
The preheat was too high
The test was performed incorrectly — bend tests rarely fail qualified procedures

Correct answer: Lack of fusion, excessive porosity, or cracking in the weld joint

Guided bend test failures indicate insufficient ductility in the weld joint, usually caused by lack of fusion, cracks, excessive porosity, or slag inclusions that open up under the bending deformation.

Guided bend tests (ASTM E190, referenced in AWS D1.1 Clause 4.8) bend a coupon around a mandrel of specified radius. The bent surface is examined for cracks, lack of fusion, or other discontinuities. Per AWS D1.1, a test fails if any crack or discontinuity exceeds 1/8 inch in any direction appears on the convex surface after bending. Failures indicate: lack of fusion (poor technique or parameter setting), cracks in the weld, excessive porosity or inclusion content, or insufficient penetration. Bend tests evaluate both root pass and fill passes through face and root bend specimens. Failure requires complete requalification testing.

AWS Welding Defects & Quality Control 1

Which NDE method is best suited for detecting surface and near-surface cracks in ferromagnetic welds?