IIW IWT key terms

The thermal energy introduced per unit length of weld, usually calculated as arc voltage times current divided by travel speed, expressed in kJ/mm. It controls cooling rate, hardness and toughness in the heat-affected zone.

The time taken for a weld region to cool from 800 °C to 500 °C. It is the practical measure used to predict transformation products, hardness and toughness in steel weldments and to set preheat and heat input limits.

The parent metal region that is not melted but whose microstructure and properties are altered by the welding thermal cycle. It commonly contains the weakest or hardest zones of a joint and governs toughness and cracking behaviour.

A formula that combines the alloying elements of a steel into a single number expressing its hardenability and susceptibility to cold cracking. Higher values demand more preheat and stricter heat input control.

Delayed cracking occurring below about 150 °C when diffusible hydrogen, a susceptible hard microstructure and tensile stress act together. It is prevented by low-hydrogen consumables, preheat, controlled heat input and post-weld hydrogen removal.

A hot crack forming in the weld metal during terminal solidification when low-melting constituents and shrinkage strain concentrate in the interdendritic liquid. It is controlled by weld metal composition, joint design and bead shape.

Stress-relief cracking in the coarse-grained heat-affected zone of certain steels, occurring during post-weld heat treatment or high-temperature service. It is linked to creep ductility loss and residual stress concentration at stress raisers.

Step-like cracking beneath a weld in plate loaded through its thickness, caused by low ductility of non-metallic inclusions in the through-thickness direction. Improved by low-sulphur steel, joint redesign and buttering.

The proportion of parent metal melted into the weld metal, expressed as a percentage of the total fused metal. It shifts weld metal composition and therefore strength, toughness and cracking resistance, especially in dissimilar or cladded joints.

The capacity of a material to be joined by a given process into a sound structure that meets service requirements under the intended fabrication conditions. It covers metallurgical, mechanical and operational aspects rather than a single material property.

A qualified document specifying the essential and non-essential variables for producing a weld to a required standard. It records ranges for consumables, current, voltage, travel speed, preheat and heat treatment that the welder must follow.

The documented evidence that a test assembly welded to a draft procedure met the required mechanical and nondestructive test results. It supports the welding procedure specification and records actual measured variables used.

Assessment of an individual welder's ability to produce acceptable welds on a defined test piece using a specific process and position. It is distinct from procedure qualification, which validates the process parameters rather than the person.

The percentage of a ten-minute period during which a power source can deliver its rated current without overheating. Welding above the rated duty cycle requires reducing current to avoid thermal damage to the equipment.

The relationship between output voltage and output current of a welding power source at steady state. Drooping characteristics suit manual metal arc welding, while flat or rising characteristics suit continuous wire processes.

The manner in which molten metal passes from electrode to workpiece, such as short-circuiting, globular, spray or pulsed. The mode determines heat input, spatter level, penetration profile and positional capability of a consumable electrode process.

Deflection of the welding arc from its intended path by magnetic fields, typically when welding near the ends of joints or with high currents. It causes uneven fusion and spatter and can be reduced by repositioning the earth connection.

Gas or gas mixture supplied to protect the molten weld pool and hot electrode from atmospheric oxygen and nitrogen. Its composition and flow rate affect arc stability, penetration shape, metal transfer and weld metal composition.

The localised volume of molten metal beneath the arc that solidifies to form the weld. Its size, fluidity and surface tension determine bead shape, penetration and defect formation.

A granular or coated mineral material that protects the molten metal, dissolves oxides and influences slag formation and arc stability. Its composition governs weld metal chemistry, especially oxygen and hydrogen content.

Non-metallic flux or oxide residue trapped in weld metal or along the fusion boundary because slag was not removed or the pool froze too rapidly. It reduces cross-section and acts as a stress raiser.

Cavities in weld metal formed by gas trapped during solidification, appearing as rounded pores distributed randomly or in clusters. Common causes include moisture, contamination, poor shielding and excessive travel speed.

A planar defect where weld metal fails to bond to the parent metal or to a previous pass. It results from insufficient heat input, poor angle, wrong travel speed or inadequate cleaning and is a serious stress raiser.

The depth to which fusion extends into the parent metal or root of a joint. Adequate penetration is essential for joint strength; excessive penetration can cause burn-through while insufficient penetration leaves an unfused root.

Examination of a weld by eye, aided by lighting, gauges and magnifiers, to detect surface discontinuities and dimensional deviations. It is the first and most widely applied inspection method and must precede other techniques.

A surface method in which a coloured or fluorescent liquid enters open discontinuities and is drawn out by a developer for visual detection. It applies to non-porous materials and reveals cracks and pores but not internal defects.

A surface and near-surface method that magnetises ferromagnetic material and applies iron particles, which gather at leakage fields around discontinuities. It detects cracks and lack of fusion but cannot inspect austenitic stainless steel.

A volumetric method using high-frequency sound waves that reflect from internal discontinuities or back walls. It detects planar defects such as cracks and lack of fusion in thick sections and requires trained interpretation.

A volumetric method in which X-rays or gamma rays pass through a weld and expose a detector, producing an image of density variations. It is sensitive to volumetric defects such as porosity and slag but less so to tight planar cracks.

The defined limits on defect type, size and frequency, and on dimensional tolerance, that determine whether a weld conforms. They are stated in the applicable standard or specification and must be agreed before inspection.

Mechanical or metallurgical examination of welded test pieces, including tensile, bend, impact and hardness tests or macrosections. It verifies procedure qualification and joint properties rather than the integrity of production welds.

A notched-bar test measuring the energy absorbed when a specimen is fractured by a swinging hammer at a specified temperature. It is used to demonstrate weld and heat-affected zone toughness, including resistance to brittle fracture.

A systematic set of hardness measurements across a weld, heat-affected zone and parent metal, often on a macrosection. It is used to verify that softening or hardening limits set for the procedure are met.

Controlled heating and holding of a welded assembly, usually below the transformation range, followed by slow cooling. It relieves residual stress, reduces hardness and diffusible hydrogen, and improves dimensional stability.

The temperature to which the parent metal is raised before welding to slow cooling and allow hydrogen to escape. It is selected from carbon equivalent, section thickness, hydrogen level and heat input.

Internal stress remaining in a structure after welding because of non-uniform heating, cooling and restraint. It can cause distortion, cracking or reduced fatigue life and is managed by sequence, heat treatment and design.

The planning of joint design, welding sequence, balancing of passes and restraint to limit unwanted movement of welded assemblies. Techniques include backstep welding, presetting and symmetric deposition around the neutral axis.

The selection of joint type, edge preparation, root gap, included angle and weld access to suit loading, thickness and process. Good design ensures fusion, minimises distortion and allows effective inspection.

A structured evaluation of hazards, exposure and consequences in a welding workplace, leading to prioritised controls. It covers fume, arc radiation, fire, electricity and noise and must be reviewed when conditions change.

Local exhaust ventilation or general ventilation that captures airborne particulate and gases at or near the arc. Effective extraction keeps exposure to manganese, chromium and other fume constituents below occupational limits.

Worn equipment such as welding helmet with correct filter shade, gloves, flame-retardant clothing and respiratory protection. It is the last line of defence after elimination, substitution and engineering controls.

Work inside an enclosed or poorly ventilated space such as a tank or pit, requiring permit control, gas testing, forced ventilation and a standby person. Welding there adds fire, fume and oxygen-displacement hazards.

Estimation of total weld cost from labour, consumables, energy, equipment, preparation and inspection, often per metre of weld. It supports comparison of processes and shows where deposition efficiency and duty factor dominate.

The ratio of deposited weld metal mass to consumed electrode or filler mass, expressed as a percentage. It accounts for spatter, stub loss and slag and strongly affects consumable cost and productivity estimates.

The use of mechanised or programmable equipment to perform welding with repeatable travel, position and parameters. It improves consistency and productivity but demands precise fit-up, joint tracking and validated procedures.

A technique using a small included angle and narrow root gap, filled with successive passes, to reduce weld metal volume and heat input. It lowers residual stress and cost but requires reliable sidewall fusion and tracking.

A solid-state process in which a rotating tool with a pin and shoulder plasticises and consolidates material along a seam without melting. It suits aluminium alloys and avoids solidification defects but leaves an exit hole.