Weldment Glossary

Running short weld segments in the opposite direction to the overall progression. Spreads the shrinkage instead of letting it pull the whole length one way.

See also Weld sequence, Distortion

Kilograms of weld metal laid per hour. It drives welding hours on a heavy weldment, which is why shops care about process choice on thick plate.

A tubular wire filled with flux, run with or without additional shielding gas. Lays metal down fast on thick sections and tolerates site conditions better than GMAW, at the cost of slag that has to be removed between passes.

See also GMAW, Slag inclusion

The wire or rod that becomes the weld. Its classification is specified in the procedure and matched to the parent material. On aluminium the filler choice also changes the colour after anodising.

See also WPS

A continuously fed wire electrode with a shielding gas. Fast, easy to automate and the most common process on general steel weldments. Sensitive to draughts because the shielding gas blows away.

See also FCAW, Shielding gas

A non-consumable tungsten electrode with filler added separately. Slow, precise and very controllable. Used on thin sections, on stainless and aluminium, and wherever weld appearance or root quality matters most.

See also Back purging

Energy put into the joint per unit length, from current, voltage and travel speed. It drives the size of the heat affected zone, the distortion and, on some materials, whether the joint keeps its properties.

See also HAZ, Distortion

The temperature of the joint when the next pass starts. Too high softens the heat affected zone, too low risks cracking on hardenable steels. Controlled by the procedure on higher strength grades rather than left to the welder.

See also Preheat, HAZ

Warming the joint before welding to slow the cooling rate and let hydrogen escape. Required on thick sections and on quenched and tempered steels, and it is a real cost and time line on a heavy part.

See also Interpass temperature, Hydrogen cracking

The arc runs under a blanket of granular flux. Very high deposition rate on long straight welds in thick plate, normally mechanised. Excellent for long seams on heavy weldments, impractical for short awkward joints.

Gas that keeps air away from the molten weld pool. Argon, carbon dioxide and mixtures are common, and the choice changes penetration, spatter and bead profile. Changing gas changes the welding procedure.

See also WPS

A consumable coated electrode. Portable, tolerant of rust and wind, slow compared with wire processes. Still used for site repairs and for positions a wire feeder cannot reach.

A narrow pass run without side to side motion. Several stringers put less total heat into a given area than one wide weave and distort less.

See also Weave bead, Heat input

A pass run with side to side motion to cover a wider area. Faster to fill a joint, higher heat input, more distortion.

See also Stringer bead, Heat input

The planned order in which joints are welded. Balanced, back step and skip sequences all exist to stop shrinkage accumulating in one direction. On a large frame the sequence is decided before the first arc and written down.

See also Distortion, Back step welding

Material machined, ground or thermally cut off the plate edge to open the joint so weld metal can reach the root. A cost line in its own right on thick plate.

A roughly triangular weld in the corner between two surfaces, most often a tee or a lap. The workhorse joint on weldments because it needs no edge preparation.

See also Leg length, Throat thickness

How accurately the parts sit relative to each other before welding starts. Fit-up decides the geometry of the finished weldment. Everything after it is heat management on a shape that is already set.

See also Tack weld, Root gap

A groove weld fused through the entire thickness of the joint. The strongest and the most expensive option, and normally the one that triggers volumetric inspection.

See also Partial penetration weld, Ultrasonic testing

A weld in a prepared groove between two members, in a V, U, bevel or J shape. Needed where the joint must carry load through the full section, and more expensive than a fillet because of the preparation and the passes.

See also Full penetration weld, Bevel

Short welds at regular spacing instead of a continuous run. Uses a fraction of the weld metal and distorts far less. Only usable where the loading and any applicable code allow it.

See also Distortion

The length of a fillet weld along either fusion face. The usual way fillet size is specified on AWS drawings. Weld volume rises with the square of the leg, so an oversized number is expensive.

See also Throat thickness, Fillet weld

A groove weld deliberately fused through only part of the thickness. Cheaper than full penetration and perfectly adequate where the design does not need the whole section.

The space between the two members at the bottom of the joint before welding. Specified by the procedure. Too wide needs more weld metal and distorts more, too tight risks a root that does not fuse.

See also Fit-up, Lack of penetration

A temporary plate at the end of a joint so the arc can be started and stopped off the workpiece. Removed and dressed afterwards.

A temporary stiffener tacked across a joint to hold alignment during welding. Removed afterwards, and the drawing should say whether the area has to be dressed flush.

A small temporary weld holding parts in position for fit-up. Whether tacks stay in the finished part or are removed and blended is a real cost question that drawings often leave unanswered.

See also Fit-up

The shortest distance from the root to the face of a fillet weld. Common on ISO drawings. Confusing leg with throat undersizes a joint by roughly thirty per cent, so the drawing has to say which it means.

See also Leg length

A circle at the elbow of a weld symbol, committing the shop to weld every face of the joint. Quick to draw and expensive to make. Use it where the joint genuinely has to be sealed.

See also Weld symbol

An accidental arc on the parent metal away from the joint. It creates a small hardened spot that can be a crack initiator, and many specifications require it to be removed and the area checked.

Cracking as the weld solidifies, often along the centreline. Linked to bead shape, restraint and alloy composition, and a known concern on certain stainless and aluminium alloys.

Cracking that appears hours or days after welding, caused by dissolved hydrogen in a hard microstructure under stress. Prevented by preheat, low hydrogen consumables and controlled cooling, which is why those are mandatory on higher strength steels.

See also Preheat

Weld metal that did not fuse to the parent metal or to a previous pass. A planar defect, structurally serious, and hard to find with radiography because it can lie in the wrong plane relative to the beam.

See also Ultrasonic testing

The weld did not reach the intended depth at the root. Usually a fit-up or procedure problem rather than a welder problem.

See also Root gap

Gas trapped in the solidifying weld, showing as rounded holes. Caused by contamination, moisture or lost gas shielding. Limited by pore size and by the proportion of area affected.

See also ISO 5817, Radiographic testing

Non-metallic residue trapped in the weld, typical of flux processes when slag is not cleaned between passes.

See also FCAW

Droplets of weld metal thrown onto the surrounding surface. Cosmetic in most cases, but it has to be removed before coating and it is abrasive on a surface that will be machined.

The angle where the weld face meets the parent metal. A steep toe concentrates stress and shortens fatigue life, which is why quality levels limit it.

See also Undercut, ISO 5817

A groove melted into the parent metal at the toe of the weld and not filled. It is a stress raiser and one of the imperfections whose allowable depth tightens sharply at higher quality levels.

See also ISO 5817, Toe angle

A measuring machine that probes points to compute features. On large weldments a portable arm or a tracker is often used instead of a fixed machine because the part will not fit on one.

See also Laser tracker

A full dimensional check of the first part against the drawing revision, reported before the rest of the batch is made. Standard practice on anything that will repeat.

A portable instrument that measures large parts by tracking a reflector. One of the few practical ways to inspect geometry across a multi-metre weldment.

See also CMM

The steel mill document giving chemistry and mechanical properties for a heat of material. Traceability means carrying that heat number through cutting and fabrication to the finished part.

See also Traceability

The area is magnetised and iron particles gather where a defect disturbs the field. Finds surface and near surface defects, faster than penetrant over a large area, and only works on ferromagnetic material.

See also PT

Any inspection that does not damage the part. On a weldment drawing, writing NDT without naming the method, the welds and the extent gives the shop nothing to price except the worst case.

See also VT, Weld map

Ultrasonic testing with a multi-element probe that steers and focuses the beam, giving a clearer picture of the weld cross section. More expensive than conventional ultrasonic testing.

See also Ultrasonic testing

Penetrant is drawn into surface breaking defects then pulled back out by a developer. Works on any non-porous material, so it is the surface method for stainless and aluminium.

See also MT

X-rays or gamma rays through the joint onto film or a detector. Excellent on volumetric defects such as porosity, poor on tight planar defects, and it produces a permanent record. Needs access to both sides and usually an exclusion zone.

See also Porosity

The ability to follow material from the mill certificate through every operation to the delivered part. Normal on structural and regulated work and a real cost in record keeping.

See also Mill certificate

Sound is sent into the material and reflections are read. Finds internal defects including planar ones such as lack of fusion. Needs a trained technician and the result depends more on the operator than the other methods.

See also Lack of fusion, Phased array

Inspection by eye against an acceptance standard, by a qualified inspector. The cheapest method, applied to every weld as normal practice, and it finds nothing below the surface.

See also ISO 5817

A drawing or table numbering each weld and stating its size, quality level and inspection requirement. An hour to produce and it removes most of the assumptions from a weldment quote.

See also NDT

Rotation of a joint because more weld metal sits on one side than the other. A single sided fillet pulls the upright of a tee towards the weld.

See also Distortion

Movement of the part caused by weld shrinkage. It appears as transverse shrinkage, longitudinal shrinkage and angular rotation. It is controlled and predicted, never eliminated.

See also Weld sequence, Machining allowance

Applying controlled local heat so the part pulls back as it cools. A legitimate skill, and some specifications restrict or forbid it, particularly on quenched and tempered steels.

The parent metal next to the weld whose properties were changed by the welding heat although it did not melt. On 6061-T6 aluminium and on quenched and tempered steels the HAZ is significantly weaker than the parent plate.

See also Heat input, Sensitisation

Heating above the transformation temperature then cooling in air to refine the grain structure. A different operation from stress relief and rarely applied to large fabricated frames.

Deliberately setting the part opposite to the expected distortion so welding pulls it to the right shape. Relies on knowing how the last one moved, which favours the shop that made it before.

Heating the weldment so its yield strength drops below the locked-in stress, letting it relax, then cooling it slowly and evenly. For carbon steel a typical cycle is 580 to 650 degrees C with about an hour per 25 mm of thickness.

See also Residual stress, Vibratory stress relief

Stress locked into the structure after welding because the heated zone could not shrink freely. It stays hidden until a cutter removes material and the part moves.

See also PWHT, Distortion

How firmly parts are held while welding. Heavy restraint keeps the part where you put it and stores the stress instead. It trades visible distortion for hidden residual stress.

See also Residual stress, Fixture

Vibrating the part at resonance to relax peak residual stresses. Fast and far cheaper than oven time, and it works differently from a thermal cycle, so it is not accepted everywhere a code requires PWHT.

See also PWHT

A low carbon austenitic stainless. The low carbon reduces chromium carbide formation in the heat affected zone, which is why L grades are the default for welded stainless.

See also 316L, Sensitisation

A low carbon austenitic stainless with molybdenum for better resistance to chlorides. The common choice for food, pharmaceutical and marine weldments.

See also 304L, Pickling

A non heat treatable aluminium alloy that gets its strength from magnesium and work hardening. It loses proportionally less across a weld than 6061-T6, which makes it a common choice for welded structures.

See also 6061-T6

A precipitation hardened aluminium alloy. Welding over ages the heat affected zone and a large part of the local strength is lost, so welded structures must be designed to the reduced allowables and not to parent plate values.

See also 5083, HAZ

The common mild structural steel in North American practice. Cheap, available and forgiving to weld. As-rolled flatness is loose, so machined faces need stock left on them.

See also S235, Machining allowance

A quenched and tempered high strength steel, yield around 690 MPa, bought when weight matters. Preheat and interpass control are mandatory and post-weld heat treatment can affect the temper.

See also S690QL, PWHT

A higher strength low alloy structural steel, yield around 345 MPa. Roughly fifty per cent stronger than A36 for a modest price increase and welded with the same processes.

See also S355

Through-hardened plate bought for wear life rather than strength. Welded within heat input and preheat limits published by the plate maker, because exceeding them removes the hardness at the joint.

A notched bar impact test measuring toughness at a stated temperature. Grades such as S355J2 carry a specified impact requirement, which is why the suffix belongs on the drawing.

See also S355

Structural tube, rectangular, square or round. Stiff for its weight and quick to fabricate. Corner radius and wall thickness tolerance decide whether a machined face on a tube is realistic.

The oxide layer on hot rolled plate. Abrasive, hard on carbide tooling and a poor base for paint. One reason a large flat face is sometimes ground rather than milled.

See also Blanchard grinding

The European mild structural steel, broadly comparable in role to A36. Grade suffixes indicate impact testing requirements.

See also A36

The European higher strength structural steel and the workhorse grade for machine frames. The J2 suffix carries an impact test at minus 20 degrees C, which matters when the drawing calls for toughness.

See also A572 Grade 50, Charpy impact test

The European quenched and tempered high strength structural steel, comparable in role to A514. Same welding discipline applies.

See also A514

Chromium carbides forming at grain boundaries when stainless is held in roughly the 450 to 850 degrees C range, leaving those boundaries short of chromium and open to corrosion. The reason low carbon and stabilised grades exist.

See also 304L, HAZ

The structural welding code for steel used widely in North America. Covers connection design, prequalified joints, qualification and inspection acceptance. Sister codes D1.2 and D1.6 cover aluminium and stainless.

See also WPS, Prequalified joint

A reference feature that dimensions and geometric tolerances are measured from. On a weldment a datum should sit on a face that will be machined, because an as-welded surface moves with the distortion.

See also GD&T, Distortion

The European standard for executing steel and aluminium structures, with execution classes EXC1 to EXC4 scaled to consequence of failure. Required for structural components placed on the European market.

See also ISO 3834

A form control requiring a surface to lie between two parallel planes. On a weldment it is achieved after machining, and it holds only if the part was stress relieved first, so the drawing should state the condition.

See also GD&T, PWHT

The language for controlling form, orientation, location and runout rather than just size. On weldments it earns its place on bore position and on flatness of machined faces.

See also Datum, Flatness

General tolerances for welded constructions. Classes A to D cover linear and angular dimensions, classes E to H cover straightness, flatness and parallelism, and the permitted deviation scales with the size of the feature.

See also Machining allowance

General tolerances for machined features, in fine, medium, coarse and very coarse classes. It applies to the features you machine, after the welded structure tolerance.

See also ISO 13920

Quality requirements for fusion welding, covering the welding organisation rather than a specific weld. Part 2 is comprehensive, part 3 standard and part 4 elementary.

See also EN 1090, WPS

The standard that grades weld imperfections into quality levels B stringent, C intermediate and D moderate, with a numerical limit for each imperfection type. Naming a level is what turns good weld into something two parties can agree on.

See also Undercut, Quality level

Extra material left on a face so a cutter can clean it up after welding has moved the part. A common starting point is 3 to 6 mm on faces and about 3 mm on the radius of a bore, and more on long or flexible sections.

See also Distortion, ISO 13920

The acceptance grade applied to a weld, most often ISO 5817 B, C or D. Applying level B across a whole frame is a common and expensive drawing error. Apply it per joint.

See also ISO 5817, Weld map

The standardised notation saying what weld goes where, built from an arrow, a reference line, a weld shape and dimensions. In AWS practice the symbol below the line applies to the arrow side.

See also Leg length, Weld all round

Flooding the underside of a stainless joint with argon so the hot root does not oxidise. Cannot be retrofitted once a section is closed, so it has to be planned before the part is welded up.

See also GTAW, 316L

Vertical spindle rotary grinding on a magnetic chuck, producing a flat face with a crosshatch pattern. Often flatter and cheaper than milling on a large plate face, and it cuts through mill scale without the tooling cost.

See also Mill scale, Flatness

Tooling that holds a part in a repeatable position, for welding or for machining. Dedicated fixtures are fast and repeatable, modular tables spread the cost across many jobs.

See also Restraint, Fit-up

Dipping the part in molten zinc at around 450 degrees C. It coats everything including bores and threads, it moves the part, and sealed cavities must be vented. On machined weldments the usual sequence is galvanise first, then machine.

See also Masking

A machine where the bridge moves over a stationary part. Suits very large envelopes such as long beams and rails.

A machine with a horizontal spindle and usually a rotary table, so several vertical faces of a heavy part can be reached by indexing rather than re-slinging it. The classic weldment machine.

See also Setup

Boring a row of holes with a single bar passing through all of them so they are coaxial by construction. Removes the alignment problem rather than managing it.

Protecting machined faces, bores and threads before coating. Manual, charged by the hour, and the source of most arguments about paint where it should not be.

See also Galvanising

A chemical treatment that removes free iron from a stainless surface and helps the protective oxide film re-form. It does not strip heat tint, so it is not a substitute for pickling after welding.

See also Pickling

Acid removal of heat tint and the chromium depleted layer beneath it on stainless. It removes material, unlike passivation. Leaving heat tint on is a common reason a stainless weldment rusts at the joint.

See also Passivation, 316L

Equipment that rotates a heavy weldment so each weld can be made in the flat position. Flat welds are faster and more consistent, so a positioner is a quality decision as well as a productivity one.

One position of the part in the machine. On a heavy weldment each additional setup means crane time, re-clamping, re-indicating the datums and an added tolerance stack. It is where large machining quotes diverge.

See also Horizontal boring mill, Datum

The EN 1090 grading that scales welding, inspection and documentation requirements with the consequence of failure. A shop certified for EXC2 is not automatically approved for EXC3 work.

See also EN 1090

An Incoterm where the buyer takes the goods at the seller premises and carries all transport cost and risk from there. Worth settling early on weldments, because a heavy frame is an expensive thing to move.

The evidence behind a WPS. A test coupon welded to the procedure and destructively tested. A WPS without a supporting PQR is an unqualified procedure, except where a prequalified joint applies.

See also WPS, Prequalified joint

A joint configuration that AWS D1.1 permits to be used without procedure qualification testing when every listed condition is met. A legitimate route, not a shortcut, and the shop should be able to name which one applies.

See also AWS D1.1, PQR

The enquiry package sent to a shop. A complete weldment RFQ carries a model and a drawing with weld symbols, the material grade, the quality level, the inspection scope, the machined features and their tolerances, the finish and the quantity.

See also Weld map

The limits of what a certificate actually covers: materials, thicknesses, processes, positions, execution classes. Asking what the scope covers is more useful than asking whether the certificate exists.

See also ISO 3834, EN 1090

The overall length, width and height of the finished part. Together with weight it is the first thing that rules a shop in or out, because a frame can be welded far larger than it can be machined.

See also Setup

A record that an individual welder passed a test, valid within ranges of process, material group, thickness, position and joint type. Our welders are certified answers nothing without the ranges.

See also WPS

An assembly made by welding parts together. A machined weldment is one where critical features are cut after welding, usually after stress relief, so the tolerance holds on the finished part rather than on the plate it came from.

See also Machining allowance, PWHT

The written instruction for making a specific weld: process, material and thickness range, joint design, position, consumable, current, preheat and pass arrangement. A welder working to a WPS is not improvising.

See also PQR, AWS D1.1