Sri Lanka NVQ Level 3 Welder Written Examination cheat sheet

Arc eye (photokeratitis) is caused by UV radiation from the arc; welding helmets must carry a filter shade matched to process and current (e.g. shade 10-13 for SMAW at higher amperages).

Ozone and nitrogen oxides form from UV action on air; ventilation must remove fumes at the arc, and confined-space welding requires gas testing and a permit before entry.

Electric shock risk rises with wet conditions and high open-circuit voltage; OCV above 80 V (or 50 V AC in damp areas) demands extra precautions and insulated electrode holders.

Shielding gases (argon, CO2, helium) displace oxygen; in confined spaces use oxygen monitoring and never use oxygen to ventilate.

Fire watch rule: combustible material within roughly 10 m must be removed or protected; hot work permits and fire extinguishers are required at the site.

Personal protective equipment order: flame-resistant clothing and leather gauntlets, welding helmet, safety glasses under the helmet, and respiratory protection for fume.

Compressed gas cylinders must be secured upright, kept away from heat, and stored with oxygen separated from fuel gases by distance or a fire-resistant barrier.

Noise, slag burns and grinding sparks are secondary hazards; grinding requires face shield plus safety glasses and guarding on the wheel.

A welding symbol consists of the reference line, an arrow pointing to the joint, and optional tail; the weld symbol sits above (other side) or below (arrow side) the reference line.

A fillet weld symbol is a right triangle; the leg size is written to the left of the symbol and the length to the right, with pitch after a hyphen for intermittent welds.

Supplementary symbols: circle at the junction means weld all around; flag means field weld; a concave or convex contour is shown by a curved line above the symbol.

A groove weld symbol names the preparation: V, bevel, U, J, square; the groove depth or root opening and included angle appear as dimensions on the symbol.

Basic views: the front view shows length and height, the top view shows length and width, and the side view shows width and height; hidden features use dashed lines.

A butt joint symbol placed on the arrow side means the weld is made on the side the arrow touches; the same symbol above the line places the weld on the opposite side.

Welding terminology: root, face, toe, leg, throat, reinforcement, penetration and heat-affected zone describe regions of a weld cross-section.

Theoretical throat of a 90-degree fillet equals 0.707 times the leg length; the actual throat includes any convexity, which is not counted as strength.

Carbon equivalent (CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15) above about 0.40 raises hardenability and cold-cracking risk, requiring preheat.

Low-carbon steel (up to about 0.25% C) welds readily; medium-carbon and high-carbon steels need preheat and controlled cooling to avoid martensite.

Austenitic stainless steel (300 series) is welded with low-carbon or stabilized grades (304L, 316L, 321, 347) to limit sensitization and carbide precipitation.

Aluminium forms a tenacious oxide film with a melting point far above the metal; it must be removed by stainless wire brushing or chemical cleaning before welding.

Edge preparation: plate edges must be clean, dry and free of scale, rust, oil and paint within at least 25 mm of the joint before welding.

Hydrogen sources (moisture, oil, rust, damp electrodes) promote cold cracking in high-strength steels; low-hydrogen consumables must be baked and stored hot.

Copper alloys conduct heat away rapidly, so preheat and higher current are used; zinc-bearing brass produces toxic fume and needs ventilation.

Weldability is judged by crack sensitivity, porosity tendency, and strength match; dissimilar metals are selected by dilution and thermal expansion compatibility.

SMAW uses a constant-current (drooping) characteristic power source; current is set on the machine and arc length is controlled by the welder's hand.

GMAW uses a constant-voltage power source with wire-feed speed controlling current; short-circuit, globular, spray and pulsed transfer depend on current density and gas.

GTAW uses a constant-current source with high-frequency or scratch start; the electrode is tungsten (EWTh-2 for DC, EWZr for AC) and filler is added separately.

AC is used for GTAW on aluminium to break the oxide with the electrode-positive half cycle; DCEN concentrates heat in the work for steel.

Oxy-acetylene flame types: neutral (ratio about 1:1), oxidizing (excess oxygen) and carburizing (excess acetylene); a neutral flame is used for most steel welding.

SAW uses granular flux and high currents (often 300-1000 A) for thick plate; the arc is buried, giving high deposition and deep penetration.

FCAW uses a flux-cored wire that may be self-shielded or gas-shielded; it gives higher deposition than SMAW and tolerates wind better than GMAW.

Equipment checks: inspect cable insulation, earth clamp contact, regulator diaphragms and torch hoses for leaks before each shift.

Electrode classification E6013: E = electrode, 60 = 60,000 psi minimum tensile strength, 1 = all-position, 3 = rutile coating and AC/DC polarity.

E7018 is a low-hydrogen iron-powder electrode; it must be stored in a heated oven (about 100-150 C) and used within a limited exposure time.

GMAW wire ER70S-6 contains higher deoxidizers (Mn, Si) than ER70S-4, making it suitable for dirty or mill-scale plate.

Shielding gas choice: 100% CO2 gives deep penetration and low cost; argon-CO2 mixes (e.g. 75/25) give smoother transfer and less spatter.

Stainless filler ER308L matches 304L base metal; ER316L is used for 316 base metal or where molybdenum corrosion resistance is needed.

Flux for SAW must be dry; damp flux causes porosity and hydrogen cracking, so it is baked before use.

Filler diameter selection follows joint thickness and position: smaller diameter for root passes and vertical-up, larger for flat fill passes.

Consumable consumption can be estimated from deposit efficiency; SMAW is roughly 60-70%, GMAW and SAW are higher, so more wire is needed than weld metal volume.

Heat input (kJ/mm) = (voltage x current x 60) / (travel speed in mm/min x 1000); higher heat input means slower cooling and a wider HAZ.

Current controls penetration and deposition; voltage controls arc length and bead width; travel speed controls bead shape and penetration profile.

For a fillet weld, leg size and throat are set by current and speed; too high a current causes undercut and spatter, too low causes lack of fusion.

A Welding Procedure Specification (WPS) records essential variables: process, base metal, filler, current range, voltage range, travel speed, preheat and gas flow.

A Procedure Qualification Record (PQR) documents the test that proved the WPS; welder qualification is separate and tests the individual's skill.

Polarity rules: DCEN (straight polarity) gives shallow penetration and is used for GTAW on steel; DCEP (reverse polarity) gives deeper penetration and cleaning action.

Gas flow rates for GMAW are typically 12-20 L/min; too little causes porosity, too much causes turbulence and entrainment of air.

Preheat temperature is selected from base metal carbon equivalent and thickness; it slows cooling to keep hardness below the cracking threshold.

Five basic joints: butt, lap, tee, corner and edge; the butt joint is preferred for full penetration and efficient load transfer.

Single-V groove needs an included angle of about 60 degrees, a root gap of 1.5-3 mm and a root face of 1-2 mm for a sound root.

Fit-up tolerances: root gap, root face and mismatch must be controlled; excessive gap increases dilution and burn-through, tight gap causes lack of penetration.

Tack welds must be of qualified quality, of adequate length, and fully fused into the root; they become part of the finished weld.

A backing bar or ceramic backing supports the root and prevents burn-through; removable backing must be removed and the area inspected.

For a lap joint the overlap should be at least three times the thinner plate thickness to develop strength.

Distortion control by fit-up: preset the parts against expected shrinkage, balance welds about the neutral axis, and use a back-step sequence.

Cleaning between passes removes slag and prevents slag inclusion; each pass must be inspected visually before the next is deposited.

Porosity is gas trapped in the weld, caused by moisture, dirt, wrong gas flow or long arc; it appears as rounded dark spots on a radiograph.

Slag inclusion is non-metallic material trapped between passes; it is prevented by cleaning each pass and using correct travel angle.

Lack of fusion (side wall or inter-run) results from low heat input, wrong angle or fast travel; it is a planar defect and is more harmful than porosity.

Undercut is a groove melted into the base metal at the toe and left unfilled; it is caused by excessive current, long arc or wrong electrode angle.

Cracks are the most serious defect; hot cracks occur during solidification, cold (hydrogen) cracks occur hours later and need preheat and low-hydrogen consumables.

Visual inspection (VT) checks bead shape, undercut, spatter and dimensions; it is done before, during and after welding.

Non-destructive methods: PT finds surface-breaking defects, MT finds surface and near-surface defects in ferromagnetic steel, UT finds internal planar defects, RT finds internal volumetric defects.

Acceptance standards define defect size limits; a defect exceeding the limit is repaired by gouging or grinding out and rewelding, then re-inspected.

Distortion types: longitudinal shrinkage, transverse shrinkage, angular distortion, bowing and buckling; each has a different control method.

Balanced welding: weld alternately on opposite sides of the neutral axis, or use a back-step (step-back) sequence to spread heat input.

Presetting (pre-bending) offsets expected angular shrinkage; restraint jigs and strongbacks hold parts until the weld cools.

Stress-relief heat treatment for carbon steel is typically at 580-650 C, held about one hour per 25 mm of thickness, then slow cooled.

Post-weld heat treatment reduces residual stress and hardness in the HAZ; it must be controlled by thermocouples and recorded on a chart.

Solution annealing for austenitic stainless steel is around 1040-1120 C followed by rapid cooling to restore corrosion resistance.

Post-weld cleaning: remove slag and spatter, brush stainless with a dedicated stainless brush, and pickle or passivate to restore the oxide film.

Peening can reduce tensile residual stress but must not be applied to the root or final pass in a way that masks defects.

Weld metal volume for a single-V butt weld is approximately area of the groove cross-section times length; add cap reinforcement and root penetration separately.

Fillet weld cross-section area = 0.5 x leg x leg; multiply by length to get volume, then by density (about 7.85 g/cm3 for steel) for mass.

Consumable mass = weld metal mass / deposit efficiency; for SMAW use about 0.65, for GMAW about 0.90, for SAW about 0.95.

Travel speed (mm/min) = electrode feed rate (mm/min) x wire cross-section area / weld cross-section area, for a given deposition.

Documentation set includes the WPS, PQR, welder qualification certificate, material certificates, inspection reports and NDT reports.

Traceability: heat numbers on mill certificates must be linked to the components; consumable batch numbers are recorded in the weld log.

A weld map records joint numbers, welder ID, date, process and inspection results so each weld can be traced to its welder.

Units and conversion: 1 inch = 25.4 mm; 1 psi = 6.895 kPa; 1 bar = 100 kPa; current in amperes, voltage in volts, heat input in kJ/mm.

Workshop layout: separate hot-work bays from flammable storage, keep walkways clear, and position welding screens to protect others from arc flash.

Hand tool checks: hammer heads must be wedged, chisels mushroomed heads ground off, and grinding wheels ring-tested and fitted with guards.

Measurement tools: steel rule, vernier caliper, try square, fillet weld gauge and taper gauge are used to check fit-up and weld size.

Material marking and cutting: mark with soapstone or marker, cut with shears, saw or thermal cutting, then grind the cut edge to remove oxide and hard zone.

Calculation example: a 6 mm fillet, 200 mm long, has throat 4.24 mm, cross-section 18 mm2 and volume 3600 mm3, about 28 g of steel.

Calculation example: heat input for 200 A, 24 V and 150 mm/min travel = (200 x 24 x 60)/(150 x 1000) = 1.92 kJ/mm.

Documentation discipline: record actual parameters used, not the nominal WPS values, so deviations can be investigated later.

Housekeeping at shift end: isolate power, close gas valves, store electrodes in the oven, and clear hot slag and offcuts from the bay.

Workshop layout: separate hot-work bays from flammable storage, keep walkways clear, and position welding screens to protect others from arc flash.

Hand tool checks: hammer heads must be wedged, chisels with mushroomed heads ground off, and grinding wheels ring-tested and fitted with guards.

Measurement tools: steel rule, vernier caliper, try square, fillet weld gauge and taper gauge are used to check fit-up and weld size.

Material marking and cutting: mark with soapstone or marker, cut with shears, saw or thermal cutting, then grind the cut edge to remove oxide and hard zone.

Calculation example: a 6 mm fillet, 200 mm long, has throat 4.24 mm, cross-section 18 mm2 and volume 3600 mm3, about 28 g of steel.

Calculation example: heat input for 200 A, 24 V and 150 mm/min travel = (200 x 24 x 60)/(150 x 1000) = 1.92 kJ/mm.

Documentation discipline: record actual parameters used, not the nominal WPS values, so deviations can be investigated later.

Housekeeping at shift end: isolate power, close gas valves, store electrodes in the oven, and clear hot slag and offcuts from the bay.