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 11666See also: How to write an ITP that works in practiceArc 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 jointsArc 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 inputAustenite
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 steelB
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 2553See also: Full penetrationC
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 1090-1See also: CE marking of steel structures under EN 1090-1CET 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 1011-2See also: Preheating in weldingCold 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 1011-2See also: Preventing hydrogen crackingCombined 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 1011-2See also: Preheating in weldingConcession
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 NCRCovered 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 2560See also: Preventing hydrogen crackingCruciform 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 jointsCTOD
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 15653See also: Offshore and marineCWI
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 14731See also: CWI vs IWID
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 17640See also: Ultrasonic testing (UT) of welded jointsDilution
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, Dissimilar metal weldsDuplex 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 17781See also: Welding duplex stainless steelE
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 10204See also: Material certificates 3.1 and 3.2 to EN 10204EN 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, -3See also: Execution classes under EN 1090-2, EN 1090 supportEssential 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 IXSee also: Essential variablesExcess 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. 504See also: Food and pharmaceuticalExecution 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 1090-2See also: Execution classes under EN 1090-2F
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 surprisesFactory 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 1090-1See also: Factory production control (FPC) under EN 1090-1Fatigue
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 13001See also: Fatigue of welded jointsFerritescope
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 E562See also: Ferrite measurement in stainless and duplex weld metalFillet 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 2553See also: Calculating the throat thickness of a fillet weldFlux 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 17632Full 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 1993-1-8See also: Full penetrationFusion 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 9015-1See also: Hardness testing of welded jointsH
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 1011-1See also: Calculating and controlling heat inputHeat 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 17781See also: Heat tint on stainless weldsHot 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. 1001See also: Welding nickel alloys and InconelI
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 148-1Inspection 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 practiceInterpass 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 13916See also: Preheating in weldingISO 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, -2See also: ISO 15614-1, WPQR qualificationISO 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 -6See also: ISO 3834 parts 2, 3 and 4ISO 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 5817See also: ISO 5817 quality levels B, C and DISO 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 -5See also: Welder qualification to ISO 9606-1ISO 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 9712See also: NDT personnel to ISO 9712J
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 9692-1See also: Joint preparationL
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. 401See also: Weld defects, Ultrasonic testing (UT) of welded jointsLamellar 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 10164See also: Full penetrationLeg 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 2553See also: Calculating the throat thickness of a fillet weldM
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 MDRN
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 15156See also: Offshore and marine, Hardness testing of welded jointsNDT 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 17635See also: Choosing the right NDT method for a welded jointNon-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 NCRNon-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 17635See also: Choosing the right NDT method for a welded joint, NDT coordinationP
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 IXSee also: ASME Section IX explained, ASME IX vs EN ISO 15614-1Passivation
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 16048See also: Heat tint on stainless weldsPorosity
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. 200See also: Weld defectsPositive 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 industryPost 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 VIIISee also: PWHTPreheating
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 1011-2See also: Preheating in weldingPressure 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/EUSee also: Welding under the PED 2014/68/EU, Pressure equipmentProcedure 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 IXSee also: The 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 managementpWPS
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 15614See also: Writing a pWPSQ
R
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, PWHTS
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 steelShielding 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 14175See also: Selecting shielding gasSlag 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. 301See also: Weld defectsStress 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 13445-4See also: PWHTSubmerged 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 4063See also: 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 1090-2See also: Planning the welding sequenceThroat 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 1993-1-8See also: Calculating the throat thickness of a fillet weldThrough 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 10164See also: Full penetrationTIG 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 4063See also: TIG welding (141) and orbital welding of pipeworkTOFD
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 10863See also: Phased array and TOFDTungsten 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. 3041See also: TIG welding (141) and orbital welding of pipeworkU
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. 5011See also: Weld defects, Fatigue of welded jointsV
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, Vendor inspection abroadVisual 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 17637See also: Visual testing of welds to ISO 17637, Visual weld inspectionW
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 logWeld 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 logWeld 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 6520-1See also: Full penetrationWeld 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 inputWeld 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 jointsWelding 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 6947See also: Welder qualification to ISO 9606-1Welding 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 IXSee also: When do you need a WPQR?, WPQR qualificationWelding 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 2553See also: Reading welding symbols to ISO 2553Workpiece 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 13916See also: Preheating in weldingWPS
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 15609-1See also: WPS development and management, WPS versus WPQRX
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 industryNo term found.
