IIW IWI-S key terms

The thermal energy introduced per unit length of weld, usually calculated as voltage × current × arc efficiency divided by travel speed, expressed in kJ/mm. It controls cooling rate, heat-affected zone width, and mechanical properties.

The portion of parent metal not melted but whose microstructure and properties are altered by welding heat. Its extent and toughness depend on heat input, material chemistry, and cooling rate.

The time taken for a weld region to cool from 800 °C to 500 °C, used as an index of transformation behaviour. Short times favour hard microstructures; long times favour softer, coarser ones.

A formula combining alloying element percentages into a single value that estimates a steel's susceptibility to hardening and cold cracking. Higher values demand preheat, higher heat input, or low-hydrogen consumables.

Delayed cracking in steel caused by the combined action of diffusible hydrogen, a susceptible hard microstructure, and tensile stress. Often appears hours after welding and is prevented by hydrogen control and preheat.

Hydrogen absorbed during welding 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 heating of the parent metal before welding to slow cooling, reduce the risk of hard microstructures and hydrogen cracking, and assist fusion. Temperature is specified in the welding procedure and verified before the arc is struck.

The temperature of the weldment immediately before the next weld pass is deposited. It is kept within a specified maximum to preserve toughness and within a minimum to control cooling and hydrogen.

A qualified document giving the variables required to make a production weld, such as process, consumable, current range, preheat, and pass sequence. It must be supported by a procedure qualification record.

The documented record of a test weld made to qualify a welding procedure, including actual variables used and the results of destructive and nondestructive testing. It is the evidence behind a WPS.

A welding parameter whose change beyond specified limits requires requalification of the procedure or the welder. Examples include process, filler classification, thickness range, and joint design.

Testing of an individual welder's ability to produce sound welds to a specified standard, using defined joint, position, and thickness conditions. Qualification is specific to process and position and must be renewed or revalidated.

The orientation of the joint relative to the welder and gravity, such as flat, horizontal, vertical, or overhead. It affects metal transfer, pool control, and which qualification ranges apply.

Gas or gas mixture supplied around the arc to exclude air and stabilise metal transfer. Composition affects penetration profile, spatter, and oxidation, and differs between argon-rich and carbon dioxide-rich mixtures.

An arc process using a continuously fed consumable wire electrode and an externally supplied shielding gas. Variants include short-circuiting, globular, spray, and pulsed transfer, each with distinct heat input and deposition behaviour.

An arc process using a non-consumable tungsten electrode and inert shielding gas, with filler added separately if required. It gives precise control and clean welds, making it common for root passes and thin sections.

A covered electrode whose coating is mainly calcium carbonate and calcium fluoride, producing low diffusible hydrogen and tough weld metal. It requires controlled storage and re-drying to keep that low-hydrogen property.

Controlled holding of covered electrodes in heated quivers or ovens, plus baking of moisture-absorbed electrodes at specified temperatures. Correct practice preserves low hydrogen content and prevents porosity and cracking.

The percentage of a ten-minute period for which a power source can operate at a stated current without exceeding its thermal rating. It determines how current must be reduced for continuous production welding.

The relationship between output voltage and current for a welding supply, described as drooping (constant current) or flat (constant voltage). It dictates arc stability, self-regulation, and suitable process applications.

The shaping of edges before welding, including bevel angle, root gap, root face, and land. It governs access, penetration, distortion, and the volume of filler required.

The geometric arrangement of members to be joined, such as butt, T, lap, corner, or edge. The configuration determines stress flow, inspection access, and the applicable welding symbols.

The clearance between the two members at the base of a joint preparation. It allows full penetration of the root pass but must be controlled to avoid burn-through or excessive weld volume.

Unintended change in shape or dimensions of a weldment caused by non-uniform heating, shrinkage, and residual stress. It is managed by balanced sequences, restraint, pre-setting, and correct fit-up.

Internal stress locked into a component after welding without external load, arising from restrained contraction of hot metal. It can promote cracking, reduce fatigue life, and be relieved by heat treatment or mechanical means.

Controlled heating of a completed weldment, usually below the transformation temperature, to relieve residual stress, temper hard zones, and reduce hydrogen. Temperature, hold time, and heating rate are specified and recorded.

The planned order in which passes, runs, or assemblies are welded. A well-chosen sequence balances shrinkage forces, limits distortion and residual stress, and supports consistent quality.

Lateral oscillation of the electrode or torch across the joint during welding. Moderate weaving widens the bead and improves fusion at sidewalls, but excessive weaving can cause slag entrapment and lower toughness.

A drawing notation showing weld type, size, length, spacing, and location relative to the joint, with a leader line and arrow. It communicates design intent to the fabricator without written notes.

Cavities in weld metal formed by entrapped gas that failed to escape before solidification. Causes include moisture, contamination, poor shielding, and excessive travel speed, and acceptance limits are set by the applicable standard.

Solid non-metallic material trapped in weld metal or along the fusion boundary, usually from incomplete removal of slag between passes or poor manipulation. It acts as a stress raiser and is detected by radiography or ultrasonics.

A planar defect where weld metal fails to bond with the parent metal or a previous pass. Caused by insufficient heat, poor access, or contamination, it is a serious stress raiser best found by ultrasonic testing.

A volumetric nondestructive method that passes ionising radiation through a weld onto film or a digital detector. Density differences reveal internal discontinuities such as porosity, slag, and cracks, with sensitivity depending on technique and geometry.

A volumetric method using high-frequency sound waves to detect and size internal discontinuities, especially planar ones. It requires trained operators, reference blocks, and careful probe selection for reliable interpretation.

A surface method where a coloured or fluorescent liquid enters open surface-breaking discontinuities and is drawn back out by a developer. It detects cracks and laps in non-porous materials but not internal defects.

A surface and near-surface method that magnetises ferromagnetic material and applies iron particles, which gather at flux leakage around discontinuities. It finds cracks and lack of fusion but applies only to ferromagnetic materials.

A destructive test pulling a specimen until fracture to determine yield strength, ultimate tensile strength, elongation, and reduction of area. It is used to qualify procedures and verify weld metal and joint strength.

A destructive test measuring the energy absorbed when a notched specimen is struck, typically by a pendulum. It assesses toughness at a specified temperature, which matters for low-temperature service and thick sections.

A mapped set of hardness readings across the weld, heat-affected zone, and parent metal. It verifies that hard, crack-susceptible zones have been tempered adequately, especially after post-weld heat treatment.

The limits defining whether a detected discontinuity is acceptable, set by the applicable code or contract. They consider defect type, size, location, and service conditions rather than requiring a perfect weld.

A failure of a product, process, or document to meet a specified requirement. It must be recorded, dispositioned, and where appropriate corrected, with the action and its verification documented.

Steps taken to eliminate the cause of a detected nonconformity so it does not recur, as distinct from merely reworking the item. It includes root-cause analysis and verification of effectiveness.

A document specifying the processes, responsibilities, inspections, and records required for a project or product. It links code requirements to hold points, witness points, and the evidence to be submitted.

A stage in fabrication where work must not proceed until a specified inspection or approval has been completed and recorded. It protects quality by preventing concealment of work before verification.

A notified stage of work that the inspector may observe if present, but which does not stop progress if the inspector is absent. It differs from a hold point in that it does not block continuation.

A record of inspection activities, findings, and disposition, including reference to drawings, procedures, and standards used. It must be traceable, factual, and signed by the responsible inspector.

The ability to link materials, consumables, and welds to their certificates, procedures, and welder identities through records. It allows investigation and recall if a problem is later discovered.

Local exhaust ventilation capturing welding fume near the arc before it enters the breathing zone. Correct hood placement and airflow are essential because welding fume contains metal oxides and gases harmful to health.

Entry into an enclosed or poorly ventilated area such as a tank or vessel, requiring risk assessment, atmospheric testing, a permit, standby personnel, and rescue arrangements. Welding inside adds fume, fire, and electrical hazards.

A formal authorisation to carry out welding, cutting, or grinding where sparks or heat could cause fire. It records fire watch, area clearance, and precautions before work starts.

Worn equipment such as welding helmet, filter, gloves, flame-retardant clothing, and respiratory protection that reduces exposure to arc radiation, spatter, fume, and heat. It supplements, but never replaces, engineering controls.