IIW IWP key terms

The thermal energy introduced per unit length of weld, usually calculated as voltage × current × arc efficiency divided by travel speed. It strongly influences cooling rate, microstructure and the risk of cracking in the heat-affected zone.

The region of parent metal that has been thermally altered by welding but not melted. Its properties change because of the peak temperature and cooling cycle it experiences, and it is where many cracking and toughness problems originate.

The speed at which a weld and its surroundings lose heat after welding, often quoted over a temperature range such as 800 to 500 degrees Celsius. It governs hardness, toughness and susceptibility to cracking in steels.

Deliberate heating of the parent metal before welding to slow cooling, reduce the risk of hydrogen cracking and improve fusion. The required temperature depends on material, thickness, joint restraint and hydrogen level.

The temperature of the weldment just before the next pass is deposited. It must be kept within limits set by the procedure, because excessive interpass temperature can degrade toughness and mechanical properties.

Delayed cracking that occurs after welding has finished, usually below about 200 degrees Celsius, when hydrogen trapped in the joint combines with a hard microstructure and residual stress. Control relies on low hydrogen, preheat and adequate heat input.

Hydrogen that remains mobile in the weld metal at room temperature and can migrate to stressed regions, promoting cold cracking. It is measured in millilitres per 100 grams of deposited metal and is minimised by dry consumables and clean surfaces.

A written document that gives the qualified welding variables for a particular joint, including process, consumables, current range, preheat and pass sequence. Welders must follow it to ensure the joint meets its specified requirements.

The documented evidence that a test weld made to a draft procedure produced acceptable results in destructive and non-destructive tests. It supports the WPS and records the actual conditions used during qualification.

Formal testing and certification confirming that an individual welder can produce welds to a required standard for specific processes, positions, materials and thicknesses. It is personal to the welder and separate from procedure qualification.

The orientation of the joint relative to the welder and gravity during welding, such as flat, horizontal, vertical or overhead. Position affects difficulty, technique and the range of qualification held by a welder.

Gas or gas mixture supplied to protect the molten weld pool and hot electrode from atmospheric contamination during gas-shielded processes. Composition affects arc stability, penetration profile, spatter and mechanical properties.

An arc process in which a continuous consumable wire electrode is fed into the joint and shielded by an externally supplied gas or gas mixture. It offers high deposition rates and is widely used for semi-automatic and robotic welding.

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 and is often used for root passes and thin materials.

A metal transfer mode in GMAW where the wire repeatedly touches the pool and detaches by short circuit. It operates at low current and suits thin material and out-of-position work but gives lower heat input and more spatter.

Any material consumed during welding, such as electrodes, filler wire, flux or shielding gas, that becomes part of the joint or protects it. Its composition and storage condition directly affect weld quality and hydrogen content.

Gas-filled cavities trapped in solidified weld metal, appearing as rounded voids on a radiograph or fracture surface. Common causes include moisture, contamination, inadequate shielding and excessive travel speed.

A planar discontinuity where weld metal fails to bond to the parent metal or to a previous pass. It is often caused by insufficient heat input, poor access, wrong electrode angle or contamination and can severely reduce joint strength.

A discontinuity or imperfection in a weld that causes the joint to fail to meet specified acceptance criteria. Not every imperfection is a defect; classification depends on the applicable standard and service requirements.

Inspection methods that reveal discontinuities or material properties without damaging the component, including visual, radiographic, ultrasonic, magnetic particle and penetrant testing. Each method detects different types and orientations of flaws.

An NDT method that transmits high-frequency sound waves into a component and analyses reflected or transmitted signals. It is effective for detecting planar flaws such as lack of fusion and for measuring thickness and depth.

An NDT method that passes X-rays or gamma rays through a component onto a detector or film, producing an image that shows internal density variations. It readily reveals volumetric flaws such as porosity and slag inclusions.

Examination of welded test pieces by cutting and mechanically testing them, for example tensile, bend, impact or hardness tests. It is used in procedure qualification and to verify that specified mechanical properties are achieved.

Measurement of a material's resistance to indentation, commonly across a weld cross-section to check for excessively hard heat-affected zones. High hardness values indicate a microstructure prone to hydrogen cracking.

A calculated value combining the effects of alloying elements on hardenability, used to estimate weldability and the preheat needed for a steel. Higher values generally mean greater cracking risk and more careful thermal control.

The capacity of a material to be welded under the imposed fabrication conditions into a joint that performs satisfactorily in service. It depends on composition, thickness, restraint, process and the skill applied.

Internal stress locked into a component after welding because of non-uniform heating, cooling and restraint. It can cause distortion, promote cracking and affect fatigue life, and may be reduced by heat treatment or controlled by sequence.

Unwanted change in the shape or dimensions of a welded assembly caused by uneven shrinkage and residual stress. It is managed by balanced sequences, jigs, pre-setting and appropriate heat input.

The degree to which a joint is prevented from moving or contracting during welding by surrounding structure, fixtures or clamps. High restraint raises residual stress and increases the risk of cracking.

Controlled heating of a completed weldment to a specified temperature, holding and cooling to relieve residual stress or temper hard microstructures. It must follow a qualified cycle to avoid harming mechanical properties.

Shaping of the joint faces, such as bevel angle, root gap and root face, before welding to allow adequate access and penetration. Correct preparation is essential for sound fusion and is defined in the procedure.

The alignment and dimensional accuracy of parts before welding, including gap, mismatch and root opening. Poor fit-up causes variable penetration, distortion and defects and can invalidate the qualified procedure.

The planned order in which passes and joints are welded across an assembly. A balanced sequence distributes heat and shrinkage, reducing distortion and residual stress in the finished structure.

The proportion of a ten-minute period for which a welding power source can operate at a given current without overheating, usually expressed as a percentage. It determines the practical current available for continuous production welding.

Local or general ventilation that removes welding fume and airborne particles from the welder's breathing zone. Effective extraction is a primary control for respiratory hazards and must be matched to the process and workplace.

Clothing and equipment worn to protect the welder from hazards, including welding helmet with filter, gloves, flame-resistant clothing and respiratory protection. It is the last line of defence after elimination and engineering controls.

A formal authorisation allowing welding or cutting in an area where fire or explosion risk exists, setting out precautions, fire watch and timing. It ensures hazards such as flammable materials and confined spaces are controlled before work starts.

The activity of scheduling welding work, allocating resources, sequencing operations and controlling progress to meet cost, quality and delivery targets. It links design requirements with shop-floor capacity and inspection needs.