ITI/NCVT Welder (Fab & Fit) (AITT Theory) flashcards

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

Duty cycle

The percentage of a 10-minute period a welding machine can run at a given current without overheating. A 60% duty cycle at 300 A allows 6 minutes welding and 4 minutes cooling.

Open circuit voltage

The voltage at the welding terminals before the arc is struck. SMAW sets typically give 50-90 V OCV; higher OCV improves arc striking but increases shock risk.

Carbon equivalent formula

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Values above about 0.40% indicate a hardenability risk, requiring preheat and low-hydrogen electrodes.

Heat-affected zone

The base metal region next to the fusion line that is heated but not melted. Its microstructure and properties change, causing softening, hardening or reduced toughness.

Neutral flame

An oxy-acetylene flame with roughly equal oxygen and acetylene, showing a bright inner cone and faint outer envelope. Used for welding mild steel.

Flashback arrestor

A device fitted at the regulator or torch that stops a flame from travelling back into the hose or cylinder. It prevents explosion after a flashback occurs.

Brazing temperature

Brazing uses a filler metal that melts above 450 C but below the melting point of the base metal. Capillary action draws the filler into a close joint.

First-angle projection

A drawing convention where the object is placed between the observer and the plane. The top view appears below the front view and the left view on the right.

Representative fraction

The ratio of drawing length to actual length, written as 1:n. A scale of 1:10 means 1 mm on the drawing represents 10 mm on the object.

Hidden line

A dashed line of medium thickness used to show edges that are not visible in a given view. Visible outlines use continuous thick lines instead.

Weld all-around symbol

A small circle placed at the junction of the reference line and arrow. It means the weld continues completely around the joint.

Field weld symbol

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

Root gap

The clearance between the two root faces of a joint before welding. It is typically 1.5-3 mm and allows full penetration of the root pass.

Tungsten electrode colour code

Green marks pure tungsten for AC aluminium welding; red marks thoriated tungsten for DC steel welding; grey or gold marks ceriated or lanthanated general-purpose electrodes.

AC TIG cleaning action

During the electrode-positive half-cycle, the arc breaks up and removes the aluminium oxide film. The balance control sets cleaning versus penetration.

Plasma arc cutting

A constricted transferred arc with a high-velocity gas jet cuts conductive metals at high speed. It cuts stainless and aluminium better than oxy-fuel cutting.

Spray transfer

A GMAW metal transfer mode with high current and argon-rich gas. Fine droplets transfer axially, giving deep penetration and high deposition, but it suits flat positions only.

Contact tip to work distance

The distance from the GMAW contact tip to the workpiece, usually 10-15 mm. Increasing it reduces current and penetration and increases spatter.

Self-shielded FCAW

A flux-cored process needing no external shielding gas. The flux generates the shielding, so it suits outdoor work where wind would blow away gas shielding.

E7018 electrode

A low-hydrogen basic-coated electrode with 70 ksi tensile strength, usable in all positions on DC+ or AC. It must be stored dry and baked before use.

Back-step welding

A distortion-control technique in which short beads are deposited opposite to the general direction of travel. Each new bead starts at the end of the previous one.

Residual stress relief

Heating carbon steel to about 600-650 C and holding for roughly one hour per 25 mm of thickness, then slow cooling, reduces locked-in welding stress.

6G position

A pipe welding position with the pipe fixed at 45 degrees to the horizontal and not rotated. It is the most demanding position for welder qualification.

Cold cracking

Hydrogen-induced cracking that occurs after the weld cools, often hours later. It is prevented by preheat, low-hydrogen electrodes and dry consumables.

Lack of penetration

A planar defect where the weld metal does not reach the root of the joint. Causes include a small root gap, large root face, low current or fast travel.

Magnetic particle testing

An NDT method using a magnetic field and iron particles to reveal surface and near-surface defects. It works only on ferromagnetic materials such as carbon steel.

Ultrasonic testing

An NDT method sending high-frequency sound waves into the weld. It detects planar defects such as cracks and lack of fusion deep in thick sections.

Bend test

A destructive test bending a welded specimen to reveal ductility and fusion defects. Face and root bends check opposite sides of the weld.

Bend allowance

BA = (pi/180) x angle x (R + K x T), where R is inside radius, T thickness and K the neutral-axis factor. It gives the arc length of the neutral axis.

Shear blade clearance

The gap between the upper and lower shear blades, about 5-10% of plate thickness. Correct clearance gives a clean edge; wrong clearance causes burrs or overload.

Heat input formula

Heat input in kJ/mm = (voltage x current x 60) / (travel speed in mm/min x 1000). It controls cooling rate, HAZ hardness and distortion.

Welding procedure specification

A document specifying process, base metal, filler, current range, voltage, gas flow, preheat and pass sequence. A procedure qualification record supports it with test data.