IIW IWE key terms

Thermal energy introduced per unit length of weld, usually expressed in kJ/mm and calculated from arc voltage, current and travel speed, with a thermal efficiency factor applied for the process used.

Time taken for the weld and heat-affected zone to cool from 800 to 500 degrees Celsius, controlling transformation products and hence hardness, toughness and cracking susceptibility in ferritic steels.

A single number combining the alloying elements of a steel, weighted by their effect on hardenability, used to judge weldability and to set preheat and interpass temperature requirements.

Delayed cracking in ferritic weldments caused by the simultaneous presence of diffusible hydrogen, a hard susceptible microstructure and tensile residual stress, often occurring hours after welding is complete.

Hydrogen absorbed in molten weld metal that remains mobile in the lattice at room temperature and can migrate to stress concentrations, measured in millilitres per 100 grams of deposited metal.

Controlled reheating of covered electrodes or flux to a specified temperature and duration to drive off absorbed moisture, thereby reducing the hydrogen content of the deposited weld metal.

Temperature to which the joint is raised before welding begins, slowing cooling, lowering hardness and allowing hydrogen to escape, and specified together with minimum interpass temperature in welding procedure specifications.

Document giving the detailed, qualified values of essential and non-essential variables that a welder must follow to produce a joint complying with the relevant standard and quality requirements.

Record of the actual variables used and the test results obtained when a welding procedure was qualified by a test piece, providing the evidence on which a welding procedure specification is issued.

A welding parameter, such as material group, filler classification, current type or heat input range, whose change beyond specified limits requires requalification of the welding procedure because it may alter joint properties.

Testing of an individual welder on a specified test piece to demonstrate the manual skill needed to produce sound joints, distinct from qualification of the procedure itself and usually valid for a limited range and period.

The proportion of a ten-minute period for which a power source or welding gun can operate at a stated current without exceeding its thermal rating, expressed as a percentage at a given ambient temperature.

The relationship between output voltage and output current of a welding power source, described as drooping, constant voltage or constant current, which determines its suitability for a given process.

The inherent tendency of a welding arc with a steeply drooping or constant-current characteristic and a wire feed system to restore its own arc length after a small disturbance, giving stable deposition.

Gas or gas mixture supplied around the arc to exclude air, stabilise the arc and influence metal transfer, penetration profile and alloying; argon, helium, carbon dioxide and oxygen are common constituents.

The manner in which molten metal passes from electrode to workpiece, for example short-circuiting, globular, spray or pulsed, determined by current density, gas composition and power source characteristics.

A consumable-electrode process in which a continuously fed wire is melted by an arc shielded by gas, giving high deposition rates and adaptability to mechanisation and robotic operation.

A tubular wire process in which the core provides slag formers, deoxidants and sometimes alloying elements, offering higher deposition than solid wire and good tolerance to outdoor conditions.

An arc process in which a blanket of granular flux covers the arc and weld pool, giving very high deposition rates, deep penetration and no visible arc radiation, used mainly for mechanised flat-position work.

An arc process using a non-consumable tungsten electrode with separate filler addition where required, giving precise control and clean welds, especially on thin sections and reactive metals.

Deflection of the arc from the joint by magnetic forces arising from asymmetric current paths or residual magnetism in the workpiece, causing inconsistent penetration and spatter.

A planar imperfection in which deposited metal fails to bond to the sidewall or to previously deposited passes, typically caused by insufficient heat input, poor technique or inadequate joint preparation.

An imperfection in which the weld metal does not extend through the full root thickness of a joint, leaving an unbonded ligament that acts as a stress raiser under service loading.

Step-like cracking beneath a weld in plate loaded through its thickness, occurring where non-metallic inclusions align in planes parallel to the rolled surface and through-thickness strain is high.

The ability of plate to accommodate strain in the short transverse direction without separating at inclusion stringers, assessed by tensile testing and improved by calcium treatment or low sulphur content.

The resistance of the surrounding structure to contraction of a weld as it cools, which raises residual stress and triaxiality and increases susceptibility to cracking in stiff joints.

Internal stress locked into a component without external load, arising from non-uniform heating, cooling or fit-up restraint, which can promote cracking and distortion or reduce fatigue life.

Planning of weld sequence, balance, pre-setting and heat input to limit unwanted shape change of a fabricated assembly, supported by jigs, fixtures and post-weld correction methods.

The capacity of a material to be joined by a given process into a sound joint with acceptable properties under the fabrication conditions intended, covering cracking, toughness and service behaviour.

The region of parent metal adjacent to the fusion boundary that has been thermally altered but not melted, whose microstructure and properties vary with peak temperature and cooling rate.

A family of stainless steels with roughly equal proportions of ferrite and austenite, giving high strength and resistance to chloride stress corrosion cracking, but sensitive to intermetallic formation and wrong phase balance.

A brittle intermetallic compound that forms in stainless steels and other alloys during prolonged exposure to elevated temperature, severely reducing toughness and corrosion resistance.

A volumetric non-destructive method in which penetrating radiation passes through a component and exposes a film or detector, revealing internal imperfections as variations in density on the image.

A volumetric non-destructive method using high-frequency sound waves introduced by a probe, detecting planar imperfections and measuring their position and size from reflected echoes.

The defined limits on imperfection type, size and frequency that determine whether a completed weld conforms to the specified quality level of the applicable standard.

A graded set of imperfection limits in a weld quality standard, selected by the designer according to service, manufacturing and economic considerations rather than by inspection method alone.

Local exhaust ventilation applied close to the arc to capture welding fume and gases before they enter the welder's breathing zone, reducing exposure to metal oxides and ozone.

A respiratory irritant produced by ultraviolet radiation acting on atmospheric oxygen, most significant in gas-shielded processes such as tungsten inert gas and plasma welding, especially in confined spaces.

Equipment worn by the welder, including eye and face protection against arc radiation, flame-retardant clothing, gloves and respiratory protection, forming the last line of defence against hazards.