Explanation: EBW requires a vacuum to avoid oxidation.
Factor NOT affecting weldability?
a) Composition
b) Thickness
c) Joint design
d) Welder’s skill
Answer: d) Welder’s skill
Explanation: Weldability is material-specific.
Arc voltage range in GMAW?
a) 10-15 V
b) 15-25 V
c) 25-35 V
d) 35-45 V
Answer: b) 15-25 V
Explanation: Typical for GMAW.
‘Dilution’ in welding?
a) Mixing of filler and base metal
b) Reduced strength
c) Decreased heat input
d) Increased speed
Answer: a) Mixing of filler and base metal
Explanation: Dilution is filler-base metal mixing.
Standards for aluminum welding?
a) ISO 9606-2
b) ISO 15614-2
c) Both a and b
d) Neither
Answer: c) Both a and b
Explanation: Cover welder and procedure qualification.
Advantage of pulsed GTAW?
a) Higher deposition
b) Better heat input control
c) Lower cost
d) Easier learning
Answer: b) Better heat input control
Explanation: Pulsed GTAW controls heat precisely.
‘Arc blow’ is?
a) Arc extinguishing
b) Arc deflection by magnetic fields
c) Excessive spatter
d) Unstable arc length
Answer: b) Arc deflection by magnetic fields
Explanation: Magnetic fields cause arc deviation.
Joint with plates at right angles?
a) Butt joint
b) Lap joint
c) T-joint
d) Corner joint
Answer: c) T-joint
Explanation: T-joint forms a right angle.
Descriptive Questions Answers
WPS vs. PQR (ISO 15614-1):
WPS: A Welding Procedure Specification outlines detailed instructions for executing a weld, including welding process, base and filler materials, joint design, preheat, interpass temperatures, welding technique, and post-weld heat treatment (PWHT). It ensures consistent weld quality and is based on the validated results of the PQR.
PQR: A Procedure Qualification Record documents the actual parameters used during a qualification test weld, along with results from mechanical tests (e.g., tensile, bend, impact) and non-destructive testing (NDT). It verifies that the WPS produces welds meeting required standards, serving as evidence of procedure qualification.
Steps to Qualify a Welder for GTAW Welding of Stainless Steel Pipes (ISO 9606-1):
Select Test Piece: Choose a representative stainless steel pipe test piece (e.g., 316L, specific diameter and thickness) matching production conditions, including joint type and welding position (e.g., 6G for pipe welding).
Prepare Test Piece: Machine or grind the pipe ends to the specified joint configuration (e.g., V-groove, root gap), ensuring cleanliness to avoid contamination.
Perform Weld: The welder executes the weld under supervision, adhering to a qualified WPS, using GTAW with appropriate filler (e.g., ER316L) and shielding gas (e.g., argon).
Non-Destructive Testing (NDT): Conduct visual inspection per ISO 17637, followed by NDT like radiographic testing (RT) or dye penetrant testing (PT) to check for surface and internal defects.
Destructive Testing: If NDT is acceptable, perform destructive tests, typically including two face bend and two root bend tests, or side bend tests for thicker pipes, plus macro-examination to assess weld integrity.
Evaluation and Certification: Compare test results against ISO 9606-1 acceptance criteria (e.g., no cracks >1.5 mm). If passed, issue a qualification certificate specifying the range of validity (material group, thickness, position).
IIW Formula: CE = C + Mn/6 + {Cr + Mo + V}/5 + \{Ni + Cu}/15
Calculation: 0.547
Weldability: A CE of ~0.55 indicates moderate weldability. Steels with CE between 0.4–0.6 may require preheating (e.g., 100–150°C for 15 mm thickness, low hydrogen) to slow cooling and prevent hydrogen-induced cracking, per EN 1011-2. Careful control of welding parameters and PWHT may also be needed for thicker sections or high-restraint joints.
Factors Influencing Shielding Gas Choice in GMAW for Carbon Steel:
Penetration: CO₂ provides deeper penetration due to higher arc energy, suitable for thicker sections, while argon-rich mixtures (e.g., 75% Ar/25% CO₂) offer shallower penetration for thinner materials.
Weld Bead Appearance: Argon-rich gases produce smoother, flatter beads, enhancing aesthetics and reducing grinding needs.
Cost: CO₂ is less expensive but may increase spatter-related costs; argon mixtures are costlier but improve quality.
Metal Transfer Mode: Spray transfer requires higher argon (e.g., 80% Ar/20% CO₂), while short-circuiting works with CO₂ or mixed gases, affecting weld quality and speed.
Causes and Prevention of Porosity in Welds:
Causes: Porosity results from gas entrapment due to contamination (oil, grease, moisture on base metal or filler), inadequate shielding gas flow, incorrect welding parameters (e.g., high voltage), or turbulent gas flow.
Prevention: Clean base metal with solvents or grinding, ensure proper gas flow (15–20 L/min), use dry consumables stored per manufacturer guidelines, optimize voltage and current, and maintain consistent torch angle to avoid turbulence.
Heat Input Concept and Effect on HAZ:
Concept: Heat input (HI) measures energy transferred to the weld, calculated as: HI = {V x I x 60} / {S x1000} kJ/mm, where V is voltage, I is current, and S is welding speed (mm/min).
Effect on HAZ: Higher HI increases HAZ width and grain size, potentially reducing toughness but improving ductility. Lower HI results in a narrower HAZ with finer grains, enhancing strength but risking cracks if too low. Per EN 1011-2, HI control is critical for material properties.
Magnetic Particle Testing (MT) Process and Application:
Process: MT detects surface and near-surface defects in ferromagnetic materials. The part is magnetized (using AC for surface, DC for subsurface), magnetic particles are applied (dry or wet suspension), and indications are observed under UV or white light.
Application: Used for welds in carbon steels, detecting cracks, seams, and laps. ISO 17638 specifies MT procedures, ensuring reliable defect identification.
Purpose of PWHT and When Required:
Purpose: PWHT relieves residual stresses, improves ductility, reduces HAZ hardness, and enhances toughness, preventing issues like stress corrosion cracking.
When Required: Required for high-carbon or alloy steels, thick sections, or critical applications (e.g., pressure vessels), as specified in ISO 15614-1, EN 13445, or project requirements, particularly when CE > 0.4 or restraint is high.
RT: Uses X-rays/gamma rays for imaging. Advantages: permanent record, detects volumetric defects. Limitations: radiation hazards, requires two-sided access, less sensitive to planar defects. ISO 17636 (RT) and ISO 17640 (UT) guide procedures.
Difference Between CJP and PJP Welds:
CJP (Complete Joint Penetration): Weld penetrates the entire joint thickness, providing maximum strength, used in critical applications like bridges or pressure vessels where full load transfer is needed.
PJP (Partial Joint Penetration): Weld penetrates only part of the thickness, suitable for non-critical joints (e.g., brackets) where design allows reduced strength, per ISO 2553.
Importance of Preheating HSLA Steels:
Preheating reduces cooling rates, preventing brittle martensite formation in the HAZ, thus minimizing hydrogen-induced cracking risks. For HSLA steels (e.g., S355), EN 1011-2 recommends preheat based on CE, thickness, and hydrogen content, typically 100–200°C for CE > 0.4.
Role of Flux in SAW:
Flux in SAW shields the weld pool from atmospheric gases, removes impurities (oxides, slag), stabilizes the arc, and influences bead shape and mechanical properties. ISO 14174 classifies fluxes, ensuring compatibility with wire and base metal.
Key Parameters in Laser Beam Welding:
Laser Power: Controls penetration depth.
Welding Speed: Affects heat input and bead width.
Focus Position: Determines beam intensity and weld quality.
Shielding Gas: Prevents oxidation (e.g., helium or argon). ISO 13919-1 specifies quality levels for laser welds.
Weldability Concept:
Weldability is the ease of producing defect-free welds, influenced by material composition, microstructure, and properties. Good weldability (e.g., low-carbon steel) allows easy welding; poor weldability (e.g., cast iron) requires special techniques due to high carbon or brittleness.
Significance of IIW CE Formula:
The IIW formula CE = C + Mn/6 + {Cr + Mo + V}/5 + \{Ni + Cu}/15, quantifies steel weldability, predicting cracking risk. Higher CE indicates greater hardenability, requiring preheating or PWHT, per EN 1011-2.
Friction Stir Welding (FSW) Process and Advantages:
Process: FSW is a solid-state process where a rotating tool generates frictional heat, plasticizing material without melting, joining metals like aluminum.
Advantages: No solidification defects, low distortion, suitable for dissimilar materials, high joint strength, per ISO 25239.
Visual Inspection Requirements (ISO 17637):
Inspect welds for surface imperfections (cracks, porosity, undercut) using adequate lighting (≥350 lux), magnification if needed, and comparison against ISO 5817 acceptance criteria. Tools like gauges ensure dimensional accuracy.
Interpreting Weld Symbol (ISO 2553):
For a fillet weld with 6 mm leg length: Symbol is a triangle on the reference line, with “z6” indicating leg length. Arrow side placement shows weld location; additional notations (e.g., intermittent) specify pattern.
Importance of Interpass Temperature:
Interpass temperature controls cooling rates between weld passes, affecting microstructure and properties. Too high causes grain growth, reducing strength; too low risks cracking