IIW IWP cheat sheet

SMAW (111): electrode coating generates shielding gas and slag; current type (AC/DC) and polarity (DCEP/DCEN) are selected by electrode class; DCEP gives deeper penetration, DCEN higher deposition for some basic electrodes.

GMAW (131): transfer modes are short-circuiting (low current, thin sheet), globular (high current, spatter-prone), spray (above transition current, argon-rich gas), and pulsed (controlled current waveform for out-of-position work).

GTAW (141): uses a non-consumable tungsten electrode; DCEN concentrates heat at the work for steel, AC provides cathodic cleaning for aluminium and magnesium; argon or helium shielding; filler added separately.

SAW (121): arc is buried under a granular flux blanket; high deposition rates and deep penetration; typically used in flat or horizontal positions; flux must be baked/dry to avoid hydrogen pickup.

FCAW (136/138): tubular wire contains flux; self-shielded (136) needs no external gas, gas-shielded (138) uses CO2 or mixed gas; higher deposition than SMAW and better out-of-position capability than SAW.

Power source characteristic: constant-current (drooping) for SMAW and GTAW; constant-voltage (flat) for GMAW and FCAW; duty cycle is rated at 60% unless stated; output at 100% duty = rated current × sqrt(0.6).

Resistance welding (21): heat generated by Joule heating Q = I²Rt at the faying surface; current, time, and electrode force control nugget size; spot, seam, and projection variants.

Oxy-fuel gas welding (311): flame types are neutral (C2H2:O2 ≈ 1:1), oxidising (excess O2), and carburising (excess C2H2); maximum neutral flame temperature in air ≈ 3100 °C for acetylene.

Carbon equivalent (CE) by IIW formula: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; CE > 0.40–0.45 generally requires preheat to avoid hydrogen-assisted cold cracking.

Hydrogen cracking requires three simultaneous factors: susceptible microstructure (martensite), diffusible hydrogen, and tensile stress; control by preheat, low-hydrogen consumables, and post-weld heat treatment or tempering.

Heat input H = (k × V × I × 60)/(1000 × v) kJ/mm, where V = volts, I = amps, v = travel speed mm/min, k = thermal efficiency (SMAW ≈ 0.8, SAW ≈ 1.0, GMAW ≈ 0.8, GTAW ≈ 0.6); high heat input coarsens grains and lowers toughness.

Austenitic stainless steels: sensitisation occurs when chromium carbides precipitate at grain boundaries in the 450–850 °C range; use low-carbon (L) grades or stabilised grades (Ti, Nb) and control interpass temperature.

Aluminium and its alloys: oxide film (Al2O3) melts at ≈ 2072 °C versus aluminium at ≈ 660 °C; AC GTAW or GMAW with argon provides cathodic cleaning; thermal conductivity is high, requiring higher heat input and preheat on thick sections.

Solidification cracking susceptibility rises with wider freezing range and impurity elements (S, P, C); use lower heat input, appropriate filler with higher Mn/S ratio, and avoid deep narrow beads.

Steel toughness in the HAZ is reduced by high heat input and by coarse prior-austenite grain size; Charpy testing at specified temperature verifies impact energy, not hardness alone.

Quenched and tempered steels (e.g., S690) require low hydrogen practices and heat input limits to avoid softening of the tempered zone and cold cracking.

Weld symbols: arrow line points to the joint, reference line carries the symbol; symbol above the reference line = weld on arrow side, below = other side; a flag at the junction indicates field weld; a circle indicates all-around weld.

Butt weld preparation: root gap, root face, and included angle determine access and penetration; typical V-groove included angle 60°, root face 1–2 mm, root gap 1–3 mm depending on process.

Fillet weld throat (a) = 0.707 × leg length for a 45° equal-leg fillet; design throat governs shear capacity.

Structural design uses limit-state or allowable-stress methods; welded connections must account for eccentricity, fatigue category, and stress concentration at weld toes.

Fatigue design: weld toe is the critical location; improve by grinding, TIG dressing, or peening; classification depends on detail category and stress range, not on static strength alone.

Distortion control: balance welding about the neutral axis, use back-step or skip sequence, preset parts against shrinkage, and use minimum necessary heat input.

Shrinkage: transverse shrinkage ≈ 1–2 mm per metre of weld for butt joints; longitudinal shrinkage accumulates with weld length; restraint raises residual stress and cracking risk.

Design for inspection: provide access for visual, RT, UT, and MT; avoid inaccessible root or backside where full penetration is required.

Weldability is the capacity of a material to be welded under fabrication conditions into a specific, suitably designed structure that performs satisfactorily in service.

Carbon steels: weldability decreases as CE rises; above CE ≈ 0.45 preheat and low-hydrogen consumables are normally required; above CE ≈ 0.6 special procedures and controls apply.

Austenitic stainless steels: avoid contamination by carbon steel tools (use dedicated stainless brushes); control interpass temperature ≤ 150 °C for most grades; purge root with argon for pipe welds.

Aluminium: remove oxide and hydrocarbons before welding; use AC GTAW or GMAW; expect high thermal conductivity and solidification shrinkage; 6xxx alloys are heat-treatable and lose strength in the HAZ unless post-weld aged.

Duplex stainless steels: balance ferrite/austenite with nickel and nitrogen; control heat input (typically 0.5–2.5 kJ/mm) and interpass temperature ≤ 150 °C; avoid excessive ferrite or sigma phase.

Cutting and preparation: thermal cutting leaves a heat-affected zone that may need grinding before welding; plasma and laser cut edges can be welded directly if square and clean.

Fit-up and alignment: misalignment increases stress concentration and reduces fatigue life; tack welds must be made with qualified procedures and consumed into the final weld or removed.

Preheat and post-weld heat treatment: preheat slows cooling to avoid martensite; PWHT relieves residual stress and tempers HAZ; typical PWHT for carbon steel 580–620 °C, controlled heating/cooling rates.

Visual testing (VT) is the first and most widely used method; it detects surface discontinuities, misalignment, undercut, and spatter; requires adequate illumination (≥ 500 lux recommended) and access.

Penetrant testing (PT) detects surface-breaking discontinuities in non-porous materials; clean surface, apply penetrant, remove excess, apply developer, inspect under appropriate light; not suitable for porous or rough surfaces.

Magnetic particle testing (MT) detects surface and near-surface discontinuities in ferromagnetic materials only; use AC for surface, DC for deeper; demagnetise after testing where required.

Radiographic testing (RT) detects volumetric discontinuities (porosity, slag, lack of fusion) by differential absorption; image quality indicators (IQIs) verify sensitivity; radiation safety controls apply.

Ultrasonic testing (UT) detects planar and volumetric discontinuities; uses piezoelectric probes and couplant; angle-beam shear waves for welds; requires calibration blocks and qualified personnel.

Acceptance criteria: ISO 5817 defines quality levels B (stringent), C (intermediate), D (moderate) for steel; ISO 10042 for aluminium; defects are assessed by type, size, and location.

Qualification of procedures: ISO 15614 series (procedure qualification by test piece) and ISO 9606 series (welder performance qualification); qualification ranges cover material group, thickness, position, and process.

Quality assurance: inspection and test plan (ITP) defines hold points, witness points, and documentation; traceability of consumables and heat numbers is required for pressure and structural work.

Welding fume contains metal oxides and gases (ozone, nitrogen oxides, carbon monoxide); use local exhaust ventilation (LEV) at the arc, general ventilation, and respiratory protection where exposure limits are exceeded.

Arc eye (photokeratitis) is caused by ultraviolet radiation; use a welding helmet with the correct shade number for the process and current (e.g., shade 10–13 for SMAW at 100–300 A).

Electric shock risk: open-circuit voltage (OCV) can exceed 80 V; use dry gloves, insulated electrode holders, and ensure the work return clamp is securely connected close to the work.

Fire and explosion: remove combustibles within 10 m, use fire blankets, and obtain a hot-work permit; cylinders must be secured upright and separated from oxidisers.

Compressed gas cylinders: acetylene cylinders must be used upright and never above 1.5 bar gauge; use flashback arrestors on torches and regulators; keep oil and grease away from oxygen fittings.

Radiation: arc welding emits UV and IR; protect bystanders with screens; in RT, use shielding, dosimeters, and controlled areas per local radiation regulations.

Noise and ergonomics: grinding and plasma cutting can exceed 85 dB(A); use hearing protection; position work to avoid awkward postures and repetitive strain.

Environmental: segregate and recycle metal scrap, spent flux, and packaging; control spillage of oils and coolants; comply with local waste and emission regulations.

Travel angle and work angle: for flat butt welding, maintain a drag angle of 5–15° for SMAW; for fillet welds, work angle ≈ 45° between plates; incorrect angles cause lack of fusion or uneven legs.

Arc length: short arc for SMAW improves penetration and reduces spatter; long arc increases voltage, widens bead, and raises spatter and undercut risk.

Current selection: too low causes lack of fusion and poor penetration; too high causes undercut, spatter, and burn-through; adjust by electrode diameter and position.

Root pass in pipe: use keyhole technique with controlled arc force; maintain consistent root gap and land; back purge with argon for stainless and reactive metals.

Weaving width should not exceed 3 × electrode diameter for SMAW to avoid slag entrapment and wide, shallow beads; use stringer beads for vertical-up.

Restart technique: for SMAW, strike ahead of the crater and back into it to avoid porosity and slag inclusions; for GMAW, use run-off tabs or crater-fill function.

Post-weld cleaning: remove slag and spatter; for stainless, use pickling paste or brush to restore corrosion resistance; for aluminium, remove smut with a stainless brush.

Visual acceptance: check bead profile, toe blend, undercut depth, spatter, and uniformity; compare against ISO 5817 quality level specified for the job.

Welding coordination: ISO 14731 defines welding coordination tasks (e.g., review of requirements, procedure selection, qualification, inspection planning) and competence levels (basic, specific, comprehensive).

Production planning: sequence welding to minimise distortion and balance workload; consider fit-up, tacking, welding, inspection, and PWHT in the route card.

Consumable control: store electrodes and flux in dry conditions; follow manufacturer's baking and holding temperatures; issue only what is needed and record batch numbers.

Documentation: welding procedure specification (WPS), procedure qualification record (PQR), welder certificates, and inspection reports must be available and traceable to the work.

Key performance indicators: arc time, deposition rate, rework rate, and first-time inspection pass rate; use them to identify training or process improvements.

Interface management: coordinate between design, fabrication, and inspection; resolve non-conformities through a defined disposition process (rework, repair, concession).

Safety supervision: ensure hot-work permits, LEV, PPE, and fire watch are in place before welding starts; stop work if conditions are unsafe.

Cost control: minimise rework and scrap by correct fit-up and procedure adherence; track consumable usage and energy where relevant.