IIW IWI-B key terms

Energy introduced per unit length of weld, normally expressed in kJ/mm and calculated from arc voltage, current and travel speed. It strongly influences cooling rate, microstructure and mechanical properties.

Time taken for the weld metal or heat-affected zone to cool from 800 °C to 500 °C. It is the practical measure of cooling rate used to predict hardness and toughness.

Region of the parent metal that has been metallurgically altered by welding heat without melting. Its properties depend on peak temperature, cooling rate and the original material condition.

Percentage of a ten-minute period during which a welding power source can operate at a stated current without overheating. It defines the usable output for a given process.

Relationship between output voltage and output current of a welding power source at steady conditions. Drooping, flat and rising shapes suit different processes and control arc stability.

Equipment that converts mains supply into welding current with the voltage and characteristic required by the process. Selection depends on process, current range, duty cycle and site conditions.

Gas or gas mixture supplied around the arc to exclude air from the molten weld pool. Composition affects penetration profile, arc stability, spatter and alloying of the weld metal.

Arc process using a continuously fed consumable wire electrode protected by shielding gas. Transfer mode, gas and wire determine deposition rate, penetration and position capability.

Rate at which filler wire is delivered to the arc, usually in m/min. Together with current it controls deposition rate and must be matched to travel speed to avoid lack of fusion.

Mineral and organic covering on a covered electrode that stabilises the arc, forms slag and shielding gas, and adds alloying elements. Its type governs position capability and hydrogen content.

Hydrogen absorbed by weld metal that remains mobile at room temperature and can diffuse into the heat-affected zone. It is the main driver of delayed cracking in susceptible steels.

Delayed brittle fracture, usually in the heat-affected zone of hardenable steels, requiring hydrogen, a susceptible microstructure and residual stress. Often appears hours after welding.

Controlled heating of the parent metal before welding to slow cooling and allow hydrogen to escape. Minimum preheat depends on steel grade, thickness, hydrogen level and restraint.

A value combining the alloying elements of a steel into a single index of hardenability and weldability. Higher values indicate greater cracking risk and a need for preheat.

Standardised measure of delta ferrite content in austenitic stainless steel weld metal, determined magnetically. Adequate ferrite resists solidification cracking but excess reduces toughness.

Chromium carbide precipitation at grain boundaries in austenitic stainless steel during heating in a critical range, leaving chromium-depleted zones susceptible to intergranular corrosion.

Localised attack along grain boundaries, typically of sensitised austenitic steel in corrosive service. Low-carbon or stabilised grades and suitable heat treatment avoid it.

Hot cracking occurring while the weld pool solidifies, when low-melting films at grain boundaries cannot accommodate contraction strain. High restraint and unfavourable composition increase risk.

Step-like cracking beneath a weld in plate with poor through-thickness ductility, driven by contraction strain in restrained T-joints. Improved steel quality and joint design reduce the risk.

Resistance of the surrounding structure to contraction of a weld as it cools, generating residual stress. High restraint raises cracking risk and may require changed sequence or preheat.

Choice of joint type, preparation, gap and included angle so the weld can be made with adequate access and penetration. It must satisfy both structural and inspection requirements.

Standardised drawing notation showing joint type, weld size, length, spacing, position and whether welding is on the arrow or other side. It transfers design intent to fabrication without ambiguity.

Qualified document giving the essential variables and detailed instructions for making a weld. It is supported by a procedure qualification record and must be available to the welder.

Record of the test welds and results used to prove that a welding procedure specification produces the required properties. It documents variables and mechanical test outcomes.

Testing of an individual welder's ability to produce acceptable welds to a defined standard, within stated ranges of process, position and thickness. It is separate from procedure approval.

A parameter whose change beyond permitted limits requires requalification of a welding procedure. Examples include process, filler classification, thickness range and heat input.

Examination of a weld and surrounding area by eye, aided by lighting, gauges and magnifiers. It detects surface discontinuities, profile faults and dimensional deviations before other testing.

Set of folding templates used to measure fillet weld leg length, throat thickness, undercut depth, misalignment and weld cap height. It provides quick, repeatable dimensional checks on site.

Limits defining whether a discontinuity is acceptable for a given application and standard. They depend on joint type, service conditions and the quality level specified.

Inspection methods such as radiographic, ultrasonic, magnetic particle and penetrant testing that reveal discontinuities without damaging the component. Method choice depends on defect type and geometry.

Volumetric inspection using high-frequency sound waves to detect internal planar discontinuities and measure thickness. It suits thick sections and crack-like defects better than radiography.

Cavities formed by gas trapped in solidifying weld metal, appearing as rounded voids. Causes include moisture, contamination, inadequate shielding and excessive travel speed.

Non-metallic slag trapped in weld metal or between passes, typically from poor inter-run cleaning or incorrect technique. It creates stress concentrations and can initiate cracking.

Planar discontinuity where weld metal fails to fuse to parent metal or to a previous pass. Low heat input, poor access, wrong angle or fast travel are common causes.

Structured identification of hazards, evaluation of likelihood and severity, and definition of controls before work starts. It must be recorded and reviewed as conditions change.

Local exhaust ventilation capturing welding fume near the arc before it enters the breathing zone. Correct hood position and airflow are essential; general ventilation alone is rarely sufficient.

Formal written authorisation for high-risk activity such as hot work or confined-space entry, stating precautions, validity and responsible persons. It links hazard control to a specific job.