Sri Lanka NVQ Level 3 Welder Written Examination flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Arc eye cause

Ultraviolet radiation from the welding arc inflames the cornea, causing photokeratitis. It is prevented by a helmet filter of the correct shade and by screens protecting nearby workers.

Confined space welding rule

Before entry, test the atmosphere for oxygen and flammable gas, isolate and ventilate, and work under a permit with a standby person outside. Shielding gas can displace oxygen.

Fire watch distance

Combustible material within about 10 metres of the hot work must be removed or protected, and a fire extinguisher plus a trained fire watch kept at the site during and after welding.

All-around weld symbol

A circle placed at the junction of the reference line and arrow means the weld continues all around the joint. It is used on pipe and box connections.

Field weld symbol

A flag at the junction of the reference line and arrow indicates the weld is made at the site of construction rather than in the fabrication shop.

Fillet weld throat formula

For a 90-degree fillet, the theoretical throat equals 0.707 times the leg length. The throat is the critical dimension for shear strength.

Carbon equivalent formula

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Values above about 0.40 indicate high hardenability and a need for preheat to avoid cold cracking.

Aluminium oxide removal

Aluminium carries a refractory oxide film that melts far above the metal. It is removed by stainless wire brushing or chemical cleaning immediately before welding to prevent lack of fusion.

Low-hydrogen electrode storage

E7018 and similar basic-coated electrodes absorb moisture. They are held in a heated oven around 100-150 C and exposed to air only for a limited time before use.

ER70S-6 wire meaning

ER indicates filler wire, 70 means 70,000 psi minimum tensile strength, S means solid wire, and 6 indicates a high level of manganese and silicon deoxidizers for dirty plate.

Constant current source use

SMAW and GTAW use drooping constant-current characteristics so arc length changes cause only small current changes. The welder controls arc length by hand.

AC for aluminium GTAW

Alternating current alternates cleaning action, when the electrode is positive and the oxide breaks down, with penetration, when the electrode is negative and heat enters the work.

Heat input formula

Heat input in kJ/mm equals voltage times current times 60, divided by travel speed in mm per minute times 1000. Higher heat input slows cooling and widens the heat-affected zone.

WPS essential variables

The welding procedure specification records process, base metal, filler, current and voltage ranges, travel speed, preheat, gas flow and position. Changes outside these ranges need requalification.

PQR versus welder qualification

A procedure qualification record proves the welding procedure produces sound joints. Welder qualification separately proves the individual's skill. Both are required before production welding.

Single-V groove dimensions

A typical single-V groove uses about 60 degrees included angle, a root gap of 1.5 to 3 mm and a root face of 1 to 2 mm to achieve a sound full-penetration root.

Tack weld requirements

Tack welds must be made with qualified consumables and parameters, be long enough to hold fit-up, and be fully fused into the final weld. Defective tacks must be removed.

Back-step welding sequence

Welding is done in short steps, each starting ahead of the previous one and progressing backward. This spreads heat and reduces distortion and residual stress.

Slag inclusion cause

Non-metallic slag trapped between passes results from poor inter-pass cleaning, low current or wrong travel angle. Each pass must be chipped and brushed before the next.

Magnetic particle testing

MT detects surface and near-surface defects in ferromagnetic steel by attracting magnetic particles to flux leakage. It cannot inspect austenitic stainless steel or aluminium.

Radiographic testing detects

RT reveals internal volumetric defects such as porosity, slag and incomplete penetration as density changes on film or digital image. Planar cracks are harder to detect.

Stress relief temperature

Carbon steel post-weld heat treatment is typically held at 580 to 650 C for about one hour per 25 mm of thickness, then cooled slowly to reduce residual stress.

Solution annealing stainless steel

Heating austenitic stainless steel to about 1040 to 1120 C and cooling rapidly dissolves carbides and restores corrosion resistance after sensitization.

Fillet weld volume calculation

Cross-section area of a fillet equals half the leg squared. Multiply by length for volume, then by steel density of about 7.85 grams per cubic centimetre for mass.

Consumable mass from deposit efficiency

Required filler mass equals weld metal mass divided by deposit efficiency. Typical values are about 0.65 for SMAW, 0.90 for GMAW and 0.95 for SAW.

Weld map purpose

A weld map numbers each joint and records welder identity, date, process and inspection result, giving traceability from the finished component back to the welder and consumable batch.

Grinding wheel ring test

Before mounting, a vitrified wheel is tapped lightly and should give a clear ring. A dull thud indicates a crack and the wheel must be discarded.

Fillet weld gauge use

A fillet weld gauge checks leg length and throat thickness against the drawing. Undersized welds fail strength requirements and must be built up.

Travel speed from deposition

Travel speed equals wire feed rate times wire cross-section area divided by weld cross-section area. It links wire feed speed to bead size and heat input.

Traceability of consumables

Electrode and wire batch numbers, with mill certificates for base metal heat numbers, are recorded in the weld log so material and consumable quality can be verified later.

Hot work permit

A permit confirms fire precautions, gas testing, ventilation and a fire watch are in place before welding starts. It is signed by an authorised person and closed after the work.

Backing bar function

A copper or ceramic backing bar supports the molten root, prevents burn-through and helps form a sound root bead. Removable backing is taken off and the area inspected.