IIW IWT cheat sheet

SMAW (111): flux-coated electrode, slag shielding; deposition efficiency typically 60-70% because stub ends and spatter are lost; usable current range set by electrode diameter (approx. 30-40 A per mm of core diameter).

GMAW (131) transfer modes: short-circuiting at low current/high inductance; globular at intermediate; spray above a transition current that scales with wire diameter and shielding gas (argon-rich gases give the lowest transition current).

TIG/GTAW (141) is an autogenous or filler-fed arc process with a non-consumable tungsten electrode; DCEN concentrates heat in the workpiece (steel, titanium), DCEP ballasts the electrode and is used only for oxide cleaning in aluminium; AC combines both.

SAW (121) achieves high deposition (often 5-15 kg/h) with granular flux and deep penetration; it requires flat or circumferential positions and is normally mechanised; flux must be baked/dry to avoid hydrogen.

FCAW (136/138) uses a tubular wire; rutile types give smooth spray-like transfer for positional work, basic types give lower hydrogen and better toughness; self-shielded variants (114) need no external gas.

Resistance spot welding (21): heat input follows I squared times R times t; the largest resistance is at the faying interface, which is why the nugget forms there; electrode force controls contact resistance and expulsion.

Power source characteristics: constant-current (drooping) sources suit SMAW/TIG; constant-voltage (flat) sources suit GMAW/SAW because arc length self-regulates through wire burn-off rate.

Heat input Q = k times (U times I) / v, where k is the thermal efficiency of the process (approx. 0.8 for SAW, 0.6-0.8 for GMAW, lower for TIG); Q is expressed in kJ/mm.

Carbon equivalent predicts hardenability and cold-cracking risk: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; values above about 0.40-0.45 % for structural steels call for preheat or low-hydrogen practice.

The iron-carbon diagram fixes the transformation temperatures: A1 (eutectoid, approx. 723 C), A3 (ferrite-to-austenite finish in hypoeutectoid steels) and the effect of alloying elements, which lower or raise these boundaries.

Austenitic stainless steels (e.g. 304, 316) have higher thermal expansion and lower thermal conductivity than carbon steel, so distortion is larger and heat input must be kept low and balanced.

Sensitisation of austenitic stainless steel occurs in the approx. 450-850 C range when chromium carbides precipitate at grain boundaries and deplete Cr locally; low-carbon (L) grades or stabilised grades (Ti, Nb) resist it.

Aluminium: oxide layer melts near 2050 C versus about 660 C for the metal, so AC TIG or dedicated cleaning action is required; high thermal conductivity demands a concentrated heat source and higher travel speed.

Hydrogen in ferritic steel is the main cause of cold cracking; it is controlled by low-hydrogen consumables, preheat, interpass control and baking of electrodes (typically 300-350 C for basic electrodes).

Solidification cracking susceptibility rises with sulphur, phosphorus and a wide freezing range; manganese/sulphur ratio above about 10 in carbon-manganese steels reduces hot-cracking risk by forming MnS instead of FeS films.

Copper alloys and nickel alloys have high thermal conductivity or low melting range respectively; nickel alloys are sensitive to sulphur and lead contamination, which causes embrittlement at grain boundaries.

Weld symbols follow ISO 2553: arrow line, reference line, dashed identification line for the 'other side'; the symbol sits on the continuous line for the arrow-side weld and on the dashed line for the other side.

Butt-weld joint preparation: square edge up to about 3-4 mm thickness; single-V for moderate thickness; double-V or U preparations reduce distortion and filler volume above roughly 20-30 mm.

Fatigue design: weld toes and roots act as stress raisers; fatigue strength is governed by detail category (FAT class in Eurocode 3 / IIW recommendations) and is largely independent of static steel strength for as-welded details.

Fillet weld throat thickness a = 0.7 times leg length z for equal-leg fillets; design resistance is based on throat area and the directional method or the simplified method in Eurocode 3.

Minimum fillet leg length is generally 3 mm and at least about 0.5 times the thinner plate thickness for stiffeners; maximum leg along a free edge is limited by plate thickness (approx. 0.7 t) to avoid edge melting.

Distortion control by design: keep welds symmetric about the neutral axis, use balanced welding sequence, minimise weld volume, place welds away from highly restrained regions, and allow for shrinkage (roughly 1 mm per metre per weld pass in butt welds).

Lamellar tearing occurs in thick plates under through-thickness strain; it is mitigated by Z-quality (through-thickness ductility) plate, joint redesign to avoid through-thickness stress, and buttering.

Buckling and plate slenderness: compression members and thin webs need stiffeners; weld-induced residual tensile stress up to yield can reduce buckling resistance, so post-weld heat treatment or vibratory stress relief may be specified.

Welding Procedure Specification (WPS) is supported by a Procedure Qualification Record (PQR) or WPQR; the WPS must be requalified when essential variables (e.g. process, filler group, thickness range, position, preheat) exceed the qualified ranges.

ISO 3834 quality requirements for fusion welding define three levels (comprehensive, standard, elementary); ISO 3834-2 (comprehensive) requires a responsible welding coordinator (IWE/IWT/IWS) and full traceability.

Essential variables for procedure qualification include base-metal group, thickness, consumable designation, shielding gas, current type/polarity, position and heat input; changes beyond specified limits require a new WPQR.

Welder qualification (ISO 9606) is position- and process-specific; a test piece qualifies a range of thicknesses and positions (e.g. a butt test in PC qualifies the lower positions and a limited thickness range).

Shop fabrication sequence: cutting and edge preparation, fit-up and tacking, root pass, fill and cap, interpass cleaning and inspection, dimensional check, then NDT and any post-weld heat treatment.

Traceability requires heat-number identification of base metal and consumable batch numbers on the WPS/PQR and on the product; consumable storage and re-drying records are part of the quality file.

Non-conformance handling: a weld defect outside acceptance criteria is repaired only after a documented repair procedure and, where required, re-inspection; repeated repairs on the same location are limited by the applicable standard.

Productivity measures: arc time ratio (arc-on time / total time), deposition rate and joint completion rate; improving fit-up and reducing rework typically raises arc time ratio more than increasing current.

The weld thermal cycle produces a heat-affected zone with distinct sub-zones: coarse-grained region near the fusion line (lowest toughness), fine-grained region, and a partially transformed region; peak temperature and cooling rate t8/5 control the microstructure.

Cooling time t8/5 (time from 800 to 500 C) determines ferrite/pearlite versus bainite/martensite formation in C-Mn steels; short t8/5 (thick plate, high heat input) can harden, long t8/5 can coarsen and reduce toughness.

Post-weld heat treatment (PWHT) relieves residual stress by holding typically at 550-650 C for a time based on thickness (about 1 h per 25 mm, minimum 1 h), with controlled heating and cooling rates.

Stress-relief cracking (reheat cracking) occurs in the coarse-grained HAZ of low-alloy steels during PWHT; it is reduced by limiting heat input, using low-alloy consumables and controlling PWHT temperature and time.

Stainless steel weld metallurgy: delta-ferrite in austenitic weld metal (typically 5-10 FN) reduces solidification cracking; the Schaeffler or WRC-1992 diagram predicts ferrite from Cr and Ni equivalents.

Duplex stainless steels need a balanced ferrite/austenite ratio (roughly 50/50) in the weld; excessive heat input or slow cooling promotes sigma phase and reduces corrosion resistance and toughness.

Hydrogen-assisted cold cracking occurs below about 200 C, often hours after welding; it requires hydrogen, a susceptible microstructure and tensile stress, so preheat and controlled cooling are the main preventive measures.

Grain growth in the HAZ follows the peak temperature; for aluminium alloys, solution treatment and artificial ageing (e.g. 6xxx series) can restore properties lost in the HAZ, otherwise the softened zone remains a weak link.

Visual testing (VT) is the first and mandatory inspection step; it detects surface discontinuities, dimensional errors, undercut, spatter and incomplete fusion at the cap, and must precede other NDT.

Radiographic testing (RT) detects volumetric defects (porosity, slag, lack of penetration); sensitivity depends on source size, film/source distance and IQI (image quality indicator) wire or step-hole type.

Ultrasonic testing (UT) detects planar defects (cracks, lack of fusion) and is sensitive to orientation; acceptance is judged by amplitude relative to a reference reflector and by length/position against the acceptance level.

Magnetic particle testing (MT) applies only to ferromagnetic materials and detects surface and near-surface defects; it requires the field to be roughly perpendicular to the defect direction.

Penetrant testing (PT) applies to non-porous materials and detects surface-breaking defects only; it is not suitable for rough or porous surfaces and does not detect subsurface flaws.

Acceptance levels in ISO 5817 define quality levels B, C and D, where B is the most stringent; ISO 10042 provides equivalent levels for aluminium welds.

Destructive tests for procedure qualification include tensile, bend, impact (Charpy), hardness and macro/micro examination; hardness surveys across the HAZ are used to check against maximum permitted values in sour-service or PWHT-qualified procedures.

Phased array UT and time-of-flight diffraction (TOFD) improve detection of planar defects; TOFD sizing accuracy depends on probe separation and beam angle, and it is often combined with pulse-echo for full coverage.

Electric shock risk: open-circuit voltage of SMAW sources can reach 80 V; the secondary circuit must be isolated, and welding in wet or confined spaces requires reduced voltage (e.g. 48 V or lower) and an isolating transformer.

Arc radiation: UV causes arc eye (photokeratitis) and skin burns; eye protection must match the process, with higher shade numbers for high-current GMAW/SAW and lower for TIG at low current.

Fume and gases: welding fume contains metal oxides and, in some consumables, chromium and nickel; local exhaust ventilation or extraction is required, and confined spaces need forced ventilation and gas testing before entry.

Fire and explosion: hot work permits, removal of combustibles within a defined radius, fire watch after welding, and isolation of flammable gas lines are standard controls.

Compressed gas cylinders: store upright and secured, separate fuel gas from oxygen, use flashback arrestors on both torch and regulator, and never use oil on oxygen fittings.

Noise, heat and ergonomics: arc processes can exceed 85 dB(A) in some operations; thermal stress requires hydration and rest breaks, and repetitive positional welding needs job rotation.

Environmental controls: welding fume extraction and filtration, proper disposal of spent flux and slag, and recycling of scrap and electrode stubs; ozone from GMAW/TIG in argon atmospheres needs ventilation.

Electrical safety for equipment: earth the workpiece and machine, inspect cables for damage, and use RCD protection on the supply; the welder's return cable must be clamped close to the weld to avoid stray currents.

Total weld cost = material cost + labour cost + consumable cost + equipment/overhead cost; for manual processes labour usually dominates, while for SAW consumables and energy are more significant.

Deposition rate (kg/h) = (wire cross-section area times wire feed speed times density); for a 1.2 mm wire at 8 m/min in steel, deposition is roughly 3-4 kg/h depending on efficiency.

Arc time ratio = arc-on time / total working time; typical manual values are 20-40%, mechanised 60-80%; raising it reduces unit cost more than raising current.

Consumable cost per metre = deposition per metre times price per kg divided by deposition efficiency; stub loss and spatter reduce efficiency, so low-hydrogen basic electrodes cost more per deposited kg than rutile.

Learning curve: repetitive welding improves productivity as operators become familiar; planned production should account for ramp-up time and reject rates falling with experience.

Make-or-buy and process selection: for long straight seams, SAW or mechanised GMAW beats manual; for short, positional or repair work, manual processes remain cheaper because of set-up time.

Energy and gas consumption: shielding gas flow is typically 10-20 L/min for GMAW; leakage and excessive flow raise cost without improving protection, and gas cost can be a significant part of the total.

Production planning uses takt time and bottleneck analysis; welding is often the bottleneck, so balancing fit-up, welding and inspection stations and pre-assembling subcomponents improves throughput.

Electrode angle: for SMAW, a work angle of about 45 degrees to the joint and a drag angle of 10-15 degrees (backhand) for downhand; TIG uses a forward push angle of about 10-15 degrees.

Arc length control: long arcs cause spatter, poor penetration and nitrogen pickup; short arcs risk electrode sticking (SMAW) or contact-tip wear (GMAW). Keep arc length roughly equal to electrode diameter.

Travel speed too fast gives a narrow, convex bead with undercut and poor fusion; too slow gives a wide, flat bead with slag entrapment and excess heat input.

Root pass control: back-purge with argon for stainless and titanium, use a consumable insert or open root with controlled gap; excessive root current causes burn-through and icicles.

Interpass temperature must be measured (contact thermometer or thermal crayon) before each pass; exceeding the maximum for stainless or duplex steels degrades corrosion resistance and toughness.

Tack welds must be of qualified quality, long enough to resist shrinkage, and fully fused into the root pass; tacks that are too small crack under restraint and become defects.

Weaving limits: keep weave width within about 3 times the electrode diameter for SMAW; excessive weaving reduces penetration and can trap slag at the weld edges.

Post-weld cleaning: remove slag and spatter, brush stainless with dedicated stainless brushes, and pickle/passivate to restore the passive layer after welding.

Friction stir welding (FSW) is a solid-state process for aluminium and other low-melting metals; it avoids fusion defects and produces a fine-grained nugget, but requires rigid backing and leaves an exit hole.

Electron beam welding (EBW) achieves deep, narrow penetration with a high vacuum and small HAZ; laser beam welding (LBW) offers high speed and precision, with keyhole mode giving deep penetration at high power density.

Underwater wet welding uses specially coated electrodes and is limited in depth and quality; hyperbaric dry welding at ambient pressure gives properties closer to atmospheric welding.

Cladding and hardfacing: overlay welding with stainless, nickel or cobalt alloys for corrosion or wear resistance; dilution must be controlled to preserve the overlay composition.

Additive manufacturing (WAAM, powder-bed) builds parts layer by layer; residual stress and anisotropy of properties are key issues, and post-build heat treatment is often required.

Resistance and solid-state processes: flash butt welding for rail and bar, explosion welding for dissimilar metals, and diffusion bonding for titanium and dissimilar joints.

Narrow-gap welding uses a narrow groove with a weaving or rotating arc to fill thick sections with low heat input and reduced distortion; it needs precise joint tracking.

Robotic and automated welding requires consistent fit-up, joint tracking (laser or arc sensing) and seam-tracking calibration; variation in gap and mismatch is the main cause of automation failure.