MMAW NC I key terms

A sudden release of intense light and heat caused by an electrical fault, such as a short circuit or poor connection. It can cause severe burns and eye damage, so welding circuits must be dry, insulated, and properly grounded.

Local exhaust ventilation that captures welding smoke at or near the arc before it reaches the welder's breathing zone. It reduces exposure to metal oxide particulates and shielding-gas decomposition products such as ozone.

The voltage present at the electrode holder or torch when the machine is on but no arc is established. Higher values increase shock risk, so many standards limit OCV for manual welding in wet or confined conditions.

A formal authorization required before any welding, cutting, or grinding that produces sparks or heat. It confirms fire watch arrangements, combustible clearance, and extinguisher placement before work begins.

A designated person who monitors for smoldering fires during hot work and for a set period afterward. The watch ensures sparks have not ignited nearby materials and that extinguishing equipment is ready.

The welding current divided by the cross-sectional area carrying it, usually expressed in amperes per square millimeter. Higher density raises melting rate and penetration but also increases heat input and burn-through risk.

The thermal energy delivered per unit length of weld, calculated as voltage times current times travel-time factor divided by travel speed. It controls cooling rate, and therefore hardness, grain structure, and distortion.

The base metal adjacent to the fusion line that is metallurgically changed by heat but not melted. Its properties depend on peak temperature and cooling rate, and it is often where cracking or hardening occurs.

How quickly a weld and its surroundings lose heat after welding. Slow cooling softens and toughens many steels, while fast cooling can produce hard, crack-sensitive martensite in carbon and low-alloy steels.

Heating the base metal to a specified temperature before welding. It slows cooling, drives off moisture, and reduces hydrogen-assisted cracking risk in thick or high-carbon-equivalent steels.

A calculated value combining carbon and other alloying elements to estimate a steel's hardenability and weldability. Higher values generally require more preheat and stricter heat input control to avoid cracking.

A hard, brittle microstructure formed when steel cools too fast for carbon to diffuse. In welds it raises hardness and cracking risk, so controlled cooling or post-weld heat treatment may be needed.

Delayed cracking caused by hydrogen trapped in the weld metal or heat-affected zone, often appearing hours after welding. Prevention includes low-hydrogen consumables, preheat, clean surfaces, and controlled cooling.

The depth the weld metal extends into the joint root or base metal. Adequate penetration is essential for joint strength, while excess penetration can cause burn-through or root reinforcement problems.

The percentage of a ten-minute period a welding machine can operate at a rated output without overheating. Exceeding it causes thermal protection trips or machine damage, so output must be reduced for continuous work.

The alphanumeric code on a covered electrode, such as E7018, that specifies tensile strength, welding position, coating type, and current polarity. Reading it correctly ensures the consumable matches the procedure.

A covered electrode with a basic coating that deposits very little diffusible hydrogen, typically requiring dry storage and baking. It is used for crack-sensitive steels and restrained joints.

The distance between the electrode tip and the workpiece. It controls arc voltage, stability, spatter, and bead shape, and must be held consistently to produce uniform welds.

Magnetic deflection of the arc away from the intended path, common in direct-current welding near corners or heavy sections. It causes poor fusion and wandering beads and is managed by changing ground location or using alternating current.

Nonmetallic material formed from flux or electrode coating that solidifies over the weld bead. It protects the cooling metal but must be fully removed between passes to prevent slag inclusions.

The way molten metal moves from electrode to workpiece in gas-shielded welding, such as short-circuiting, globular, spray, or pulsed. The mode affects heat input, spatter, penetration, and positional capability.

A gas or gas mixture supplied around the arc to exclude atmospheric oxygen and nitrogen. Composition and flow rate determine arc stability, transfer mode, penetration profile, and weld cleanliness.

The rate at which filler wire is fed into the arc, usually in meters per minute. It directly controls deposition rate and, together with voltage, sets arc length and transfer behavior.

The paired settings of arc voltage and welding current that determine bead shape and stability. Voltage mainly affects width and arc length, while current mainly affects penetration and deposition.

An arc welding process using a tubular wire filled with flux, with or without external shielding gas. It offers high deposition rates and good outdoor performance, but produces slag that must be cleaned.

A flux-cored electrode whose flux generates its own shielding gas, so no external gas cylinder is needed. It suits outdoor and windy conditions but typically produces more fume and spatter.

An arc process using a non-consumable tungsten electrode and an inert shielding gas, with filler metal added separately if required. It gives precise control and clean welds on thin sections and reactive metals.

The non-consumable electrode in gas tungsten arc welding that carries the arc. Its composition, tip shape, and condition strongly influence arc stability, current capacity, and weld bead shape.

A method of initiating a gas tungsten arc with a high-voltage, high-frequency pulse that jumps the gap without touching the workpiece. It prevents tungsten contamination and is standard for critical work.

The width of material removed by a cutting torch or process. Kerf width depends on tip size, gas pressure, and travel speed, and it must be allowed for when marking cut lines.

In oxy-fuel cutting, the backward lean of the cutting oxygen stream relative to travel direction. Too much drag leaves a curved cut edge and slag, while slight drag is normal at proper speed.

The interchangeable nozzle that shapes the preheat flames and the central cutting oxygen jet. Its size is matched to plate thickness, and a dirty or damaged tip causes poor cut quality.

A backfire is a momentary pop as the flame extinguishes and relights; a flashback is flame travel back into the torch or hose. Flashback arrestors and prompt shutdown are essential safeguards.

The intentional space between two parts at the joint root before welding. It allows penetration to the root, and its size must match the procedure to avoid incomplete fusion or burn-through.

The un-beveled vertical portion at the edge of a prepared joint, also called the land. It supports the root pass and helps prevent burn-through, but too much land can cause incomplete root penetration.

The angle between the prepared edge of one part and a plane perpendicular to the surface. It creates access for the electrode and controls how much filler is needed to fill the groove.

The standardized drawing notation showing weld type, size, length, location, and reference line. Correct interpretation is essential because symbols define what the inspector will accept.

Solidified nonmetallic slag trapped between weld passes or between weld and base metal. It weakens the joint and is prevented by cleaning each pass and using proper travel technique.

Cavities in weld metal caused by trapped gas, appearing as rounded pores on the surface or in radiographs. Causes include moisture, contamination, poor shielding, and incorrect gas flow.

Any interruption in the normal structure of a weld or base metal, such as porosity, slag, or undercut. A discontinuity becomes a defect only when it exceeds acceptance criteria.

Unwanted change in shape or dimensions caused by uneven heating and cooling during welding. It is controlled through balanced sequences, fixturing, tacking, and limiting heat input.