# Welding glossary: 107 terms explained > A glossary of 107 welding terms: the meaning as the standard states it, explained in plain language, with the standard it comes from. From throat thickness. Source: https://dehaasprojects.com/en/welding-glossary/ Updated on: 2026-11-04 In welding technology a misunderstood word quickly turns into a rejected weld or a discussion with the inspection body. This glossary gives the meaning of each term as the standard states it, explained in plain language, with a reference to the standard it comes from. Is your term missing, or does a definition not quite fit your situation? Just call us and we will work it out for you. Search a welding term [A](#lb-A)[B](#lb-B)[C](#lb-C)[D](#lb-D)[E](#lb-E)[F](#lb-F)[H](#lb-H)[I](#lb-I)[J](#lb-J)[L](#lb-L)[M](#lb-M)[N](#lb-N)[P](#lb-P)[Q](#lb-Q)[R](#lb-R)[S](#lb-S)[T](#lb-T)[U](#lb-U)[V](#lb-V)[W](#lb-W)[X](#lb-X) ## A ### Acceptance criterion The predefined limit beyond which a measured value or detected indication is no longer acceptable. Without a defined criterion an inspection result cannot be judged. Standard: ISO 5817, ISO 11666 See also: [How to write an ITP that works in practice](/en/knowledge-centre/how-to-write-an-itp/) ### Arc blow Deflection of the arc by magnetic fields in the workpiece, often caused by residual magnetism or a poorly placed earth clamp. It leads to irregular penetration and lack of fusion. See also: [Magnetic particle testing (MT) of welded joints](/en/knowledge-centre/mt-magnetic-particle-testing/) ### Arc voltage The voltage across the arc during welding, in volts. Together with current and travel speed it determines heat input. Higher voltage gives a wider, flatter bead with less penetration. See also: [Calculating and controlling heat input](/en/knowledge-centre/calculating-heat-input/) ### Austenite The face centred cubic phase of iron, stable in carbon steel above roughly 727 degrees Celsius and, in sufficiently alloyed stainless steel, also at room temperature. Austenite is tough, non-magnetic and not hardenable. See also: [Welding austenitic stainless steel](/en/knowledge-centre/welding-304-316-stainless/) ## B ### Back step welding A technique in which short lengths are welded opposite to the direction of progression. It reduces net shrinkage and therefore distortion on long seams. See also: [Controlling weld distortion](/en/knowledge-centre/controlling-weld-distortion/), [Planning the welding sequence](/en/knowledge-centre/welding-sequence-planning/) ### Backing gas The gas used to purge the root side of a weld to prevent oxidation, usually argon or a nitrogen hydrogen mixture. Residual oxygen is measured rather than estimated. Standard: ISO 14175 See also: [Welding austenitic stainless steel](/en/knowledge-centre/welding-304-316-stainless/), [Food and pharmaceutical](/en/industries/food-pharmaceutical/) ### Butt weld A weld between two parts lying in the same plane, with or without joint preparation. With full penetration the joint transfers the full plate strength. Standard: ISO 2553 See also: [Full penetration](/en/knowledge-centre/full-penetration-requirements/) ## C ### CE marking The marking by which a manufacturer declares that a construction product complies with the harmonised European standard. For load bearing steel structures it requires a certified FPC system to EN 1090-1. Standard: EN 1090-1 See also: [CE marking of steel structures under EN 1090-1](/en/knowledge-centre/ce-marking-steel-structures/) ### CET carbon equivalent A carbon equivalent expressing a steel's susceptibility to cold cracking, used in the preheat calculation of EN 1011-2. CET weights manganese and molybdenum more heavily than the older CEV formula. Standard: EN 1011-2 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/) ### CEV carbon equivalent The carbon equivalent to the IIW formula, used to estimate weldability and cold cracking risk of steel. It appears on the material certificate and is an input for the preheat calculation. Standard: EN 1011-2 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/), [Material certificates 3.1 and 3.2 to EN 10204](/en/knowledge-centre/material-certificates-3-1-3-2/) ### Cold crack A crack forming hours to days after welding through the combination of hydrogen, a hard structure and tensile stress. Also called hydrogen cracking or delayed cracking. Standard: EN 1011-2 See also: [Preventing hydrogen cracking](/en/knowledge-centre/preventing-hydrogen-cracking/) ### Combined thickness The sum of the material thicknesses meeting in a joint, measured at a fixed distance from the weld. An input for the preheat calculation, because it determines how quickly heat is conducted away. Standard: EN 1011-2 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/) ### Concession Written approval to use a product that does not fully meet the specification. It may only be granted by the party that set the requirement and is recorded in the dossier. See also: [The NCR](/en/knowledge-centre/ncr-non-conformity/) ### Cooling time t8/5 The time in which the weld cools from 800 to 500 degrees Celsius. It links heat input, thickness and preheat to the resulting microstructure and is therefore the key quantity in EN 1011-2. Standard: EN 1011-2 See also: [Calculating and controlling heat input](/en/knowledge-centre/calculating-heat-input/), [Welding fine grain steel](/en/knowledge-centre/welding-high-strength-steel-s460-s690/) ### Covered electrode (111) Manual arc welding with a consumable covered electrode. Process 111 to ISO 4063. Insensitive to wind and therefore suited to site work; requires dry storage because of hydrogen. Standard: ISO 4063, ISO 2560 See also: [Preventing hydrogen cracking](/en/knowledge-centre/preventing-hydrogen-cracking/) ### Cruciform joint A joint where a plate is welded perpendicularly between two others. Loaded perpendicular to the rolling direction, making it a classic situation for lamellar tearing and a critical fatigue detail. See also: [Fatigue of welded joints](/en/knowledge-centre/fatigue-of-welded-joints/) ### CTOD Crack Tip Opening Displacement: a fracture mechanics test measuring the critical opening at a crack tip. Required for offshore work, heavy sections and low design temperatures. Standard: BS 7448, ISO 15653 See also: [Offshore and marine](/en/industries/offshore-marine/) ### CWI Certified Welding Inspector to AWS QC1: the American qualification for welding inspectors. The European counterpart is the IWI under the IIW scheme, with levels B, S and C. Standard: AWS QC1, ISO 14731 See also: [CWI vs IWI](/en/knowledge-centre/cwi-vs-iwi-welding-inspector/) ## D ### DAC curve Distance Amplitude Correction: a sensitivity curve in ultrasonic testing correcting for the fact that an identical flaw at greater depth returns a weaker echo. Without DAC or DGS an echo height has no meaning. Standard: ISO 17640 See also: [Ultrasonic testing (UT) of welded joints](/en/knowledge-centre/ut-ultrasonic-testing/) ### Delta ferrite A small amount of ferrite in austenitic weld metal, typically 3 to 10 FN, which prevents hot cracking during solidification. Too little risks cracking, too much costs toughness and corrosion resistance. Standard: ISO 8249, DIN EN 1600 See also: [Ferrite measurement in stainless and duplex weld metal](/en/knowledge-centre/ferrite-measurement-stainless/), [Welding austenitic stainless steel](/en/knowledge-centre/welding-304-316-stainless/) ### Dilution The extent to which parent material mixes with the weld metal, expressed as a percentage. On corrosion resistant overlays, dilution lowers the alloy content and therefore the corrosion resistance of the layer. See also: [Welding nickel alloys and Inconel](/en/knowledge-centre/welding-nickel-alloys-inconel/), [Dissimilar metal welds](/en/knowledge-centre/dissimilar-metal-welds/) ### Duplex stainless steel Stainless steel with roughly equal parts austenite and ferrite. It combines high strength with good chloride corrosion resistance but demands strict heat input control to preserve the phase balance. Standard: ISO 17781 See also: [Welding duplex stainless steel](/en/knowledge-centre/welding-duplex-stainless/) ## E ### EN 10204 The standard for inspection documents on metallic products. Type 2.2 is a test report, 3.1 an inspection certificate issued by the manufacturer and 3.2 one countersigned by an independent party. Standard: EN 10204 See also: [Material certificates 3.1 and 3.2 to EN 10204](/en/knowledge-centre/material-certificates-3-1-3-2/) ### EN 1090 The European standard for the execution of steel and aluminium structures. Part 1 covers conformity assessment and CE marking, part 2 the technical requirements for steel, part 3 those for aluminium. Standard: EN 1090-1, -2, -3 See also: [Execution classes under EN 1090-2](/en/knowledge-centre/en-1090-execution-classes/), [EN 1090 support](/en/services/en-1090-support/) ### Essential variable A parameter whose change beyond the permitted range invalidates the qualification, such as material group, process, thickness, position or heat treatment. A change requires new or supplementary qualification. Standard: ISO 15614-1, ASME IX See also: [Essential variables](/en/knowledge-centre/wps-essential-variables/) ### Excess penetration Weld metal protruding too far on the root side. In piping it obstructs flow and in hygienic applications it makes the weld impossible to clean. Standard: ISO 5817 nr. 504 See also: [Food and pharmaceutical](/en/industries/food-pharmaceutical/) ### Execution class (EXC) A four level classification, EXC1 to EXC4, which in EN 1090-2 sets the severity of all execution requirements: weld quality level, NDT extent, tolerances and traceability. Where unspecified, EXC2 applies. Standard: EN 1090-2 See also: [Execution classes under EN 1090-2](/en/knowledge-centre/en-1090-execution-classes/) ## F ### Factory Acceptance Test The inspection at the manufacturer where the client establishes compliance before shipment. It typically covers document review, dimensional checks, functional testing and assessment of the final dossier. See also: [FAT and final inspection without surprises](/en/knowledge-centre/fat-final-inspection/) ### Factory Production Control The documented system by which a manufacturer demonstrates that production is controlled and the product matches the specification. A prerequisite for CE marking under EN 1090-1. Standard: EN 1090-1 See also: [Factory production control (FPC) under EN 1090-1](/en/knowledge-centre/factory-production-control/) ### Fatigue Crack growth under repeated loading at stresses far below yield. In welded joints it is not the strength of the weld metal but the geometry of the weld toe that determines life. Standard: EN 1993-1-9, EN 13001 See also: [Fatigue of welded joints](/en/knowledge-centre/fatigue-of-welded-joints/) ### Ferritescope An instrument that determines ferrite content in austenitic or duplex weld metal by magnetic induction, expressed in FN or volume percent. It must be used on a smooth, clean weld. Standard: ISO 8249, ASTM E562 See also: [Ferrite measurement in stainless and duplex weld metal](/en/knowledge-centre/ferrite-measurement-stainless/) ### Fillet weld A weld in the corner between two intersecting surfaces, with a triangular cross section. Strength is governed by the throat thickness; penetration into the root is generally not required. Standard: ISO 2553 See also: [Calculating the throat thickness of a fillet weld](/en/knowledge-centre/fillet-weld-throat-calculation/) ### Flux cored wire (136) A tubular wire filled with flux, welded under shielding gas. It gives a higher deposition rate than solid wire and better positional weldability, with slag that must be removed. Standard: ISO 4063, ISO 17632 ### Full penetration weld A joint in which weld metal is fused over the full material thickness. Structurally the strongest joint and required wherever the full plate strength must be transferred. Standard: ISO 5817, EN 1993-1-8 See also: [Full penetration](/en/knowledge-centre/full-penetration-requirements/) ### Fusion line The boundary between molten weld metal and unmelted parent material. Immediately beside it lies the coarse grained zone, where hardness surveys expect the highest reading. Standard: ISO 9015-1 See also: [Hardness testing of welded joints](/en/knowledge-centre/weld-hardness-testing/) ## H ### Heat affected zone (HAZ) The zone in the parent material beside the weld that has not melted but whose structure and properties have been altered by the welding heat. Often the weakest or hardest part of the joint. See also: [Calculating and controlling heat input](/en/knowledge-centre/calculating-heat-input/), [Hardness testing of welded joints](/en/knowledge-centre/weld-hardness-testing/) ### Heat input The energy per unit length of weld, in kJ/mm, calculated from voltage, current, travel speed and the process efficiency factor. It governs cooling rate and therefore the resulting properties. Standard: EN 1011-1 See also: [Calculating and controlling heat input](/en/knowledge-centre/calculating-heat-input/) ### Heat tint The discolouration formed on stainless steel beside and on a weld through oxidation at elevated temperature. The colour runs from straw through blue to grey black and indicates how chromium depleted the oxide layer has become. Standard: AWS D18.2, ISO 17781 See also: [Heat tint on stainless welds](/en/knowledge-centre/stainless-heat-tint-pickling/) ### Hold point A point in the process where work may not continue until the designated party has released it. Unlike a witness point, where work may proceed. See also: [How to write an ITP that works in practice](/en/knowledge-centre/how-to-write-an-itp/), [Fabrication inspection](/en/services/fabrication-inspection/) ### Hot crack A crack forming during solidification of the weld metal, when remaining liquid between the grains is pulled apart. Promoted by sulphur, phosphorus and an unfavourable solidification range. Standard: ISO 6520-1 nr. 1001 See also: [Welding nickel alloys and Inconel](/en/knowledge-centre/welding-nickel-alloys-inconel/) ## I ### Image quality indicator (IQI) A calibrated wire or hole indicator placed on the component during radiography. Visibility of a specified wire proves the exposure achieved sufficient sensitivity. Standard: ISO 19232 See also: [Image quality in radiography](/en/knowledge-centre/iso-19232-image-quality/), [Radiographic testing (RT) of welded joints](/en/knowledge-centre/rt-radiographic-testing/) ### Impact energy The energy in joules absorbed by a notched specimen at fracture in a Charpy pendulum test. A measure of toughness at a given temperature and essential at low design temperatures. Standard: ISO 148-1 ### Inspection and test plan The document setting out, per production step, what is checked, by whom, against which standard, with which acceptance criterion and which record, including hold and witness points. See also: [How to write an ITP that works in practice](/en/knowledge-centre/how-to-write-an-itp/) ### Interpass temperature The temperature of the workpiece immediately before the next run is deposited. A maximum protects against grain growth and property loss; a minimum coincides with the preheat temperature. Standard: EN 1011-2, ISO 13916 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/) ### ISO 14731 The standard for welding coordination: the tasks and responsibilities of a welding coordinator and the knowledge level required. From EXC2 in EN 1090-2 a qualified welding coordinator is mandatory. Standard: ISO 14731 See also: [The welding coordinator under ISO 14731](/en/knowledge-centre/welding-coordinator-iso-14731/), [Hire a welding coordinator](/en/services/welding-coordinator/) ### ISO 15614 The standard series for welding procedure qualification by procedure test. Part 1 covers steel and nickel, part 2 aluminium. It defines the test pieces, the testing and the range of qualification. Standard: ISO 15614-1, -2 See also: [ISO 15614-1](/en/knowledge-centre/iso-15614-1-explained/), [WPQR qualification](/en/services/wpqr-qualification/) ### ISO 3834 The standard series for quality requirements in fusion welding, with three levels: comprehensive (part 2), standard (part 3) and elementary (part 4). It defines what a welding company must control, not how a weld should look. Standard: ISO 3834-1 t/m -6 See also: [ISO 3834 parts 2, 3 and 4](/en/knowledge-centre/iso-3834-parts/) ### ISO 4063 The standard assigning a number to each welding process, such as 111 for covered electrode, 121 submerged arc, 135 MAG with solid wire, 136 flux cored and 141 TIG. Those numbers appear in every WPS. Standard: ISO 4063 See also: [MAG welding process 135 and cored wire processes 136 and 138](/en/knowledge-centre/gmaw-mag-process-135/) ### ISO 5817 The standard setting limits for weld imperfections in steel, with quality levels B (stringent), C and D (moderate). The level follows from loading and consequences of failure, not from habit. Standard: ISO 5817 See also: [ISO 5817 quality levels B, C and D](/en/knowledge-centre/iso-5817-quality-levels/) ### ISO 9606 The standard for qualification of welders in manual and partly mechanised welding. It tests the skill of the person, in contrast to procedure qualification, which tests the procedure. Standard: ISO 9606-1 t/m -5 See also: [Welder qualification to ISO 9606-1](/en/knowledge-centre/welder-qualification-iso-9606/) ### ISO 9712 The standard for qualification and certification of NDT personnel, with level 1 for performing under supervision, level 2 for evaluating and reporting and level 3 for writing procedures. Standard: ISO 9712 See also: [NDT personnel to ISO 9712](/en/knowledge-centre/iso-9712-ndt-personnel/) ### IWE, IWT, IWS International Welding Engineer, Technologist and Specialist: the three knowledge levels for welding coordinators under the IIW scheme. The required level follows from steel grade, thickness and execution class. Standard: ISO 14731 See also: [The welding coordinator under ISO 14731](/en/knowledge-centre/welding-coordinator-iso-14731/), [Hire a welding coordinator](/en/services/welding-coordinator/) ## J ### Joint preparation The shape given to the parts to be joined: V, X, U, J or I, with included angle, root face and gap. The choice determines the volume of weld metal, the shrinkage and arc accessibility. Standard: ISO 9692-1 See also: [Joint preparation](/en/knowledge-centre/joint-preparation-iso-9692/) ## L ### Lack of fusion Absence of fusion between weld metal and parent material or between adjacent runs. It is a planar defect and therefore structurally dangerous, and often hard to detect with radiography. Standard: ISO 6520-1 nr. 401 See also: [Weld defects](/en/knowledge-centre/weld-defects-causes/), [Ultrasonic testing (UT) of welded joints](/en/knowledge-centre/ut-ultrasonic-testing/) ### Lamellar tearing A crack parallel to the plate surface, caused by shrinkage stress pulling perpendicular to the rolling direction on inclusion layers in the steel. Prevented with through thickness quality steel and adapted joint design. Standard: EN 1011-2, EN 10164 See also: [Full penetration](/en/knowledge-centre/full-penetration-requirements/) ### Leg length (z) The length of the triangle leg in the cross section of a fillet weld. For an equal leg fillet the throat is roughly 0.7 times the leg length; confusing the two is a common error. Standard: ISO 2553 See also: [Calculating the throat thickness of a fillet weld](/en/knowledge-centre/fillet-weld-throat-calculation/) ## M ### MAG welding (135) Metal Active Gas: arc welding with a continuously fed solid wire under an active shielding gas. Process 135 to ISO 4063, the most widely used process in fabrication. Standard: ISO 4063 See also: [MAG welding process 135 and cored wire processes 136 and 138](/en/knowledge-centre/gmaw-mag-process-135/) ### Manufacturing Record Book The final dossier of a project: every document proving the product was made to specification, from material certificates and qualifications to NDT reports, heat treatment charts and non-conformities. See also: [The MRB and MDR](/en/knowledge-centre/mrb-mdr-structure/) ### Martensite A hard, brittle structure formed when austenite cools too quickly to transform into ferrite and pearlite. In the HAZ of a weld, martensite is the direct cause of cold cracking. See also: [Hardness testing of welded joints](/en/knowledge-centre/weld-hardness-testing/), [Preventing hydrogen cracking](/en/knowledge-centre/preventing-hydrogen-cracking/) ### Material group The classification of base materials to ISO/TR 15608 into groups with comparable welding behaviour, from group 1 for ordinary structural steel to group 8 for austenitic stainless and 21 and above for aluminium. Standard: ISO/TR 15608 See also: [How to determine whether an existing WPQR covers your application](/en/knowledge-centre/wpqr-validity-range/) ## N ### NACE MR0175 The standard for materials in sour service, also known as ISO 15156. It limits the hardness of weld and HAZ, usually to 250 HV10, to prevent sulphide stress cracking. Standard: ISO 15156 See also: [Offshore and marine](/en/industries/offshore-marine/), [Hardness testing of welded joints](/en/knowledge-centre/weld-hardness-testing/) ### NDT extent The percentage of welds examined with a given method, defined per weld type and execution class. Where sampling is used, the action on finding a defect must also be defined. Standard: EN 1090-2, ISO 17635 See also: [Choosing the right NDT method for a welded joint](/en/knowledge-centre/choosing-ndt-method/) ### Non-conformity report A record of a departure from specification, with description, cause, proposed disposition and its approval. Disposition can be repair, rework, rejection or acceptance by concession. See also: [The NCR](/en/knowledge-centre/ncr-non-conformity/) ### Non-destructive testing (NDT) Examination methods that assess the weld without damaging it: visual (VT), penetrant (PT), magnetic particle (MT), radiographic (RT) and ultrasonic (UT), each with its own sensitivity and limitation. Standard: ISO 17635 See also: [Choosing the right NDT method for a welded joint](/en/knowledge-centre/choosing-ndt-method/), [NDT coordination](/en/services/ndt-coordination/) ### Notified body An organisation notified by the authorities to carry out conformity assessment under a European directive or regulation, for example the PED or the Construction Products Regulation for EN 1090. See also: [Pressure equipment](/en/industries/pressure-equipment/), [CE marking of steel structures under EN 1090-1](/en/knowledge-centre/ce-marking-steel-structures/) ## P ### P-number The ASME grouping of base materials with comparable weldability, comparable to the material groups of ISO/TR 15608 but with a different classification and different boundaries. Standard: ASME IX See also: [ASME Section IX explained](/en/knowledge-centre/asme-section-ix-explained/), [ASME IX vs EN ISO 15614-1](/en/knowledge-centre/asme-ix-vs-iso-15614/) ### Passivation Restoring the chromium oxide film on stainless steel after pickling or machining so corrosion resistance returns. Achieved chemically or by exposing clean material to oxygen. Standard: ASTM A967, ISO 16048 See also: [Heat tint on stainless welds](/en/knowledge-centre/stainless-heat-tint-pickling/) ### Porosity Gas cavities in the weld metal formed by gas that could not escape during solidification. Causes include moisture, grease, rust, insufficient gas shielding or a leaking gas line. Standard: ISO 6520-1 nr. 200 See also: [Weld defects](/en/knowledge-centre/weld-defects-causes/) ### Positive material identification Measurement of a component's chemical composition to rule out material mix-up, usually with a handheld XRF analyser. It must also be applied to weld metal, not just parent material. See also: [Petrochemical and process industry](/en/industries/petrochemical-process-industry/) ### Post weld heat treatment Heat treatment after welding, usually stress relief, to reduce residual stress, lower HAZ hardness and allow hydrogen to escape. Cycle and rates must be recorded. Standard: EN 13445-4, ASME VIII See also: [PWHT](/en/knowledge-centre/pwht-post-weld-heat-treatment/) ### Preheating Heating the workpiece before welding to slow cooling, limit martensite formation and let hydrogen diffuse out. The temperature follows from carbon equivalent, thickness and hydrogen content. Standard: EN 1011-2 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/) ### Pressure Equipment Directive Directive 2014/68/EU for pressure equipment. It classifies equipment in categories I to IV and sets, per category, the conformity assessment module and the extent of notified body involvement. Standard: 2014/68/EU See also: [Welding under the PED 2014/68/EU](/en/knowledge-centre/ped-welding-requirements/), [Pressure equipment](/en/industries/pressure-equipment/) ### Procedure Qualification Record The ASME term for the record of a welding procedure qualification: the parameters actually used and the test results. The European equivalent is called a WPQR. Standard: ASME IX See also: [The procedure qualification record (PQR)](/en/knowledge-centre/procedure-qualification-record-pqr/) ### Punch list The list of outstanding items found at an inspection or handover, with the responsible party, the disposition and the deadline per item. Category A blocks handover, category B does not. See also: [Punch list management](/en/knowledge-centre/punch-list-management/) ### pWPS Preliminary Welding Procedure Specification: the provisional procedure used to weld the test coupon. If testing passes, it becomes a definitive WPS via the WPQR. Standard: ISO 15609, ISO 15614 See also: [Writing a pWPS](/en/knowledge-centre/how-to-write-a-pwps/) ## Q ### Quality control plan The project document describing how quality is assured, who is responsible for what and which standards apply. The ITP is usually an annex to it. See also: [The quality control plan for your fabrication project](/en/knowledge-centre/quality-control-plan/) ## R ### Range of qualification The range of thicknesses, diameters, materials, positions and process variants covered by a completed qualification. Welding outside that range means the work is formally not qualified. Standard: ISO 15614-1, ISO 9606-1 See also: [Qualification range for thickness and diameter under EN ISO 15614-1](/en/knowledge-centre/qualification-range-thickness-diameter/), [How to determine whether an existing WPQR covers your application](/en/knowledge-centre/wpqr-validity-range/) ### Residual stress Stress remaining in a structure after loading is removed, caused by uneven shrinkage during welding. It adds to service stress and promotes cracking. See also: [Controlling weld distortion](/en/knowledge-centre/controlling-weld-distortion/), [PWHT](/en/knowledge-centre/pwht-post-weld-heat-treatment/) ## S ### Sensitisation The formation of chromium carbides at grain boundaries in austenitic stainless between roughly 450 and 850 degrees, leaving them chromium depleted and corrosion prone. Prevented by L grades and low heat input. See also: [Welding austenitic stainless steel](/en/knowledge-centre/welding-304-316-stainless/) ### Shielding gas The gas that shields the weld pool and arc from the air. Inert in MIG and TIG (argon, helium), active in MAG through additions of carbon dioxide or oxygen, which stabilise the arc and influence penetration. Standard: ISO 14175 See also: [Selecting shielding gas](/en/knowledge-centre/selecting-shielding-gas/) ### Slag inclusion Slag trapped between runs or in the root because it was not fully removed before the next run. Most common with covered electrodes and submerged arc welding. Standard: ISO 6520-1 nr. 301 See also: [Weld defects](/en/knowledge-centre/weld-defects-causes/) ### Stress relief annealing A heat treatment holding the structure at a temperature below the transformation point so residual stresses relax. For steel usually 550 to 620 degrees, with controlled heating and cooling rates. Standard: EN 13445-4 See also: [PWHT](/en/knowledge-centre/pwht-post-weld-heat-treatment/) ### Submerged arc welding (121) Arc welding with the arc burning beneath a flux bed, with very high deposition rate and an efficiency factor of 1.0. Suited to long, straight seams in the flat position. Standard: ISO 4063 See also: [Submerged arc welding (121)](/en/knowledge-centre/submerged-arc-welding-121/) ## T ### Tack weld A short weld holding parts temporarily in position. Tacks are welded under the same procedure as the main weld and must be consumed or removed, because they are a common source of cracking. Standard: EN 1090-2 See also: [Planning the welding sequence](/en/knowledge-centre/welding-sequence-planning/) ### Throat thickness The height of the largest isosceles triangle that fits within the cross section of a fillet weld, measured from the theoretical root. Throat thickness is the design dimension for fillet weld strength, not the leg length z. Standard: ISO 2553, EN 1993-1-8 See also: [Calculating the throat thickness of a fillet weld](/en/knowledge-centre/fillet-weld-throat-calculation/) ### Through thickness property Steel with guaranteed properties in the through thickness direction, designated Z15, Z25 or Z35. Required where a weld introduces tensile stress perpendicular to the plate surface, to prevent lamellar tearing. Standard: EN 10164 See also: [Full penetration](/en/knowledge-centre/full-penetration-requirements/) ### TIG welding (141) Arc welding with a non-consumable tungsten electrode under inert gas, with or without filler. Process 141 to ISO 4063, the preferred method for root runs, thin sections and stainless steel. Standard: ISO 4063 See also: [TIG welding (141) and orbital welding of pipework](/en/knowledge-centre/tig-141-orbital-welding/) ### TOFD Time of Flight Diffraction: an ultrasonic technique determining flaw height from the time difference between waves diffracted at the upper and lower tips. Highly accurate in height, with dead zones at the surfaces. Standard: ISO 10863 See also: [Phased array and TOFD](/en/knowledge-centre/phased-array-tofd/) ### Traceability The demonstrable ability to trace every material used and every weld back to its certificate, welder and procedure. A hard requirement in higher execution classes and for pressure equipment. Standard: EN 1090-2 See also: [Material certificates 3.1 and 3.2 to EN 10204](/en/knowledge-centre/material-certificates-3-1-3-2/), [Weld map and weld log](/en/knowledge-centre/weld-map-weld-log/) ### Tungsten inclusion A particle of tungsten entering the weld pool in TIG welding because the electrode touched the pool or the filler. It appears as a bright spot on a radiograph. Standard: ISO 6520-1 nr. 3041 See also: [TIG welding (141) and orbital welding of pipework](/en/knowledge-centre/tig-141-orbital-welding/) ## U ### Undercut A groove along the weld toe where parent material has melted away without being filled by weld metal. It acts as a notch and initiates fatigue cracks under fluctuating load. Standard: ISO 6520-1 nr. 5011 See also: [Weld defects](/en/knowledge-centre/weld-defects-causes/), [Fatigue of welded joints](/en/knowledge-centre/fatigue-of-welded-joints/) ## V ### Vendor inspection Inspection at a supplier on behalf of the client, to establish that production follows the purchase specification. It covers document review beforehand, attendance at hold points and final inspection. See also: [Vendor inspection](#lb-vendor-inspectie), [Vendor inspection abroad](/en/knowledge-centre/vendor-inspection-abroad/) ### Visual testing (VT) The first and mandatory examination method for every weld: assessment by eye, with aids and gauges, under adequate lighting. It finds surface defects and shape deviations but nothing beneath the surface. Standard: ISO 17637 See also: [Visual testing of welds to ISO 17637](/en/knowledge-centre/iso-17637-visual-testing/), [Visual weld inspection](/en/knowledge-centre/visual-weld-inspection-method/) ## W ### Weld log A record capturing, per weld, who made it, under which procedure, when, with which material and what examination was performed. Indispensable for traceability and release. See also: [Weld map and weld log](/en/knowledge-centre/weld-map-weld-log/) ### Weld map A drawing on which every weld is given a unique number, linked to the applicable procedure and the required examination. The basis for the weld log and for traceability. See also: [Weld map and weld log](/en/knowledge-centre/weld-map-weld-log/) ### Weld root The side of the weld lying deepest in the joint, opposite the cap. The root is often the most structurally critical and simultaneously the hardest to assess without examination. Standard: ISO 6520-1 See also: [Full penetration](/en/knowledge-centre/full-penetration-requirements/) ### Weld run A single pass of the arc depositing weld metal. A multi-run weld consists of a root run, fill runs and a capping run, each with its own parameters and heat input. See also: [Calculating and controlling heat input](/en/knowledge-centre/calculating-heat-input/) ### Weld toe blending The transition from weld metal to parent material at the surface. A smooth transition with a generous radius reduces notch effect; a sharp transition is where the crack starts under fluctuating load. See also: [Fatigue of welded joints](/en/knowledge-centre/fatigue-of-welded-joints/) ### Welding operator The person who sets up and monitors a mechanised or automatic welding process without guiding the arc by hand. Qualified to ISO 14732 rather than ISO 9606. Standard: ISO 14732 See also: [Operator qualification to ISO 14732 for mechanised and orbital welding](/en/knowledge-centre/operator-qualification-iso-14732/), [Robot welding](/en/knowledge-centre/robot-welding-qualification/) ### Welding position The orientation in which welding takes place, designated to ISO 6947: PA flat, PB horizontal fillet, PC horizontal, PE overhead, PF vertical up and PG vertical down. Position is an essential variable. Standard: ISO 6947 See also: [Welder qualification to ISO 9606-1](/en/knowledge-centre/welder-qualification-iso-9606/) ### Welding procedure qualification The process in which a test coupon and testing demonstrate that a welding procedure produces a joint with the required properties. The result is a WPQR or PQR. Standard: ISO 15614, ASME IX See also: [When do you need a WPQR?](/en/knowledge-centre/when-do-you-need-a-wpqr/), [WPQR qualification](/en/services/wpqr-qualification/) ### Welding symbol The standardised representation on a drawing indicating weld type, size, length, position and any supplementary requirements. Its position relative to the reference line determines which side is welded. Standard: ISO 2553 See also: [Reading welding symbols to ISO 2553](/en/knowledge-centre/welding-symbols-iso-2553/) ### Witness point A point in the process where a party is invited to attend, but where work may proceed if they do not appear. In contrast to a hold point. See also: [How to write an ITP that works in practice](/en/knowledge-centre/how-to-write-an-itp/) ### Workpiece temperature The temperature of the material at the location and moment of welding, measured with a contact thermometer or temperature indicating crayon. Measured at a prescribed distance from the joint, not on the weld itself. Standard: ISO 13916 See also: [Preheating in welding](/en/knowledge-centre/preheating-when-required/) ### WPQR Welding Procedure Qualification Record: the report stating what was actually welded during qualification and which test results were achieved. It underpins one or more WPSs. Standard: ISO 15614-1 See also: [WPS versus WPQR](/en/knowledge-centre/wps-vs-wpqr-difference/), [How to determine whether an existing WPQR covers your application](/en/knowledge-centre/wpqr-validity-range/) ### WPS Welding Procedure Specification: the working document for the welder containing every defined variable, from material and consumable to current, voltage, position, preheat and interpass temperature. Standard: ISO 15609-1 See also: [WPS development and management](/en/services/wps-development/), [WPS versus WPQR](/en/knowledge-centre/wps-vs-wpqr-difference/) ## X ### XRF analysis X-ray fluorescence: a measurement determining elemental composition from the characteristic radiation a material emits. The basis of handheld PMI, with limited sensitivity to light elements. See also: [Petrochemical and process industry](/en/industries/petrochemical-process-industry/) No term found. ## A question about a welding standard, a WPS or an inspection? Just ask it. You get a personal answer from a welding coordinator who has done the work, not from a salesperson. [Send your request](/en/quote/) [Call 06 29 72 37 91](tel:+31629723791) --- DEHAAS Inspection, Manufacturing & Welding Consultancy, Rypsterdyk 2, 9036 JG Menaam. Phone 06 29 72 37 91, e-mail cdehaas@dehaasprojects.com, https://dehaasprojects.com.