IIW IWI-C cheat sheet

SMAW: arc between covered electrode and workpiece; the cellulose or rutile coating stabilises the arc and shields the melt; current range typically 80-250 A for 3.2-4.0 mm electrodes.

GMAW transfer modes: short-circuiting (low current, thin sheet), globular (medium), spray (above transition current, argon-rich gas, deep penetration); pulsed spray extends spray range to lower mean current.

GTAW uses a non-consumable tungsten electrode (EWTh-2 with 2% thoria, EWLa-1 with lanthanum); DCEN for steel, AC for aluminium to break the oxide; separate filler wire is added manually or by cold/hot wire feed.

SAW runs under a granular flux blanket at 300-1500 A; high deposition rate, deep penetration, only flat or horizontal positions; flux must be baked/dry to avoid hydrogen porosity.

FCAW: tubular wire with flux core; self-shielded (no external gas) or gas-shielded (CO2 or mixed); rutile, basic and metal-cored types differ in toughness and hydrogen content.

Heat input formula: HI (kJ/mm) = k x U x I x 60 / (1000 x v), where U in volts, I in amperes, v in mm/min, k = 1.0 for DC, 0.6-0.85 for AC depending on waveform.

Resistance spot welding: heat generated by J = I squared x R x t; electrode force, current and time are the three main parameters; nugget diameter should be roughly 4 to 5 times the square root of sheet thickness in mm.

Power source characteristics: constant-current (drooping) for SMAW and GTAW, constant-voltage (flat) for GMAW and FCAW; OCV must be high enough to restrike but below electrical safety limits.

Carbon equivalent (IIW): CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; values above about 0.40-0.45 in % indicate increased cold-cracking risk and need for preheat or low-hydrogen practice.

Hydrogen cracking requires three simultaneous factors: susceptible microstructure (martensite), diffusible hydrogen above a critical level, and tensile restraint stress; remove any one factor to prevent cracking.

Hot cracking (solidification cracking) is promoted by high sulphur and phosphorus, wide freezing range, deep weld shape (high depth/width ratio) and high restraint; manganese and low heat input help.

Austenitic stainless steel: sensitisation occurs when chromium carbides precipitate at grain boundaries in the 450-850 C range, depleting chromium; use low-carbon (L) grades or stabilised (Ti, Nb) grades.

Aluminium: tenacious oxide layer (melting point about 2050 C) must be removed by AC GTAW or mechanical/chemical cleaning; high thermal conductivity demands higher heat input and preheat for thick sections.

Ferritic steels: heat-affected zone toughness falls with high heat input and coarse prior austenite grain size; normalising or tempering heat treatment restores toughness.

Duplex stainless steel: roughly 50/50 austenite-ferrite; balance is upset by too fast cooling (excess ferrite) or too slow cooling (sigma phase, 600-900 C); control heat input and interpass temperature.

Solidification modes in ferritic steel welds depend on Creq/Nieq ratio: A, AF, FA, F; ferrite in austenitic welds (about 5-10 FN) resists solidification cracking.

Butt joints in tension: full penetration is required for full-strength design; partial penetration reduces effective throat and introduces a crack-like root defect, so design must account for it.

Fillet weld throat: for equal-leg fillet, throat a = 0.707 x leg length z; design capacity uses throat area times allowable stress; minimum leg size depends on thicker plate thickness per code tables.

Fatigue design: detail category (FAT class) depends on weld geometry, toe radius, load direction and NDT; S-N curve slope changes at 5 million cycles (constant amplitude) and a cut-off limit applies.

Stress concentration: abrupt section changes, weld toes, and incomplete penetration raise local stress; grinding the toe or using TIG dressing improves fatigue life by smoothing the transition.

Lack of fusion and lack of penetration are planar defects perpendicular to the load; they are more damaging under fatigue than rounded porosity of the same size.

Buckling: slender compression members and thin plates are governed by slenderness ratio and plate slenderness (width/thickness); welding-induced distortion reduces buckling resistance.

Lamellar tearing occurs in thick plates with through-thickness stress and inclusion stringers; use Z-quality (through-thickness tested) plate and reduce restraint or change joint design.

Weld symbols: ISO 2553 uses a reference line with solid and dashed sides; the arrow side is drawn with a solid line, the other side with a dashed line; the tail carries the process or standard reference.

pWPS to WPQR to WPS: a preliminary WPS is tested, results recorded in a WPQR (procedure qualification record), and the WPS is then issued from the qualified range.

ISO 15614-1 covers procedure qualification for steel; essential variables include base metal group, thickness range, consumable, position, heat input range and preheat/interpass temperature.

Thickness qualification: a test piece of thickness t qualifies a range; typical rules qualify from about 0.5t to 2t for butt welds, with limits on maximum qualified thickness.

Welder qualification under ISO 9606-1 is specific to process, position, joint type and consumable group; a passed test covers a defined thickness and diameter range, usually for a limited validity period (commonly 2-3 years with periodic confirmation).

Positions: ISO uses PA (flat), PB (horizontal vertical), PC (horizontal), PD, PE (overhead), PF (vertical up), PG (vertical down); ASME uses 1G to 6G with F, H, V, O.

Preheat is measured and maintained before and during welding; interpass temperature must be controlled (especially for stainless and duplex) and checked with contact thermometers or thermal chalk.

Distortion control: balanced welding sequence, back-step technique, pre-setting, minimum number of passes, and stress-relief heat treatment after welding where required.

WPS essential variables: change of base metal group, filler classification, shielding gas composition beyond permitted range, or current type normally requires requalification.

Quality assurance is process-based (procedures, audits, documentation); quality control is product-based (inspection and testing of the actual weld).

Visual inspection is performed before, during and after welding; it detects surface defects such as undercut, overlap, spatter, and incorrect weld profile, and is the first line of NDT.

Destructive tests on procedure qualification include tensile, bend (root and face), impact (Charpy V-notch), hardness survey (HV10) and macro/micro examination.

Hardness limits: common acceptance is 350 HV10 maximum in the HAZ for carbon and carbon-manganese steels; higher limits apply to some stainless and duplex grades.

Dimensional inspection checks fit-up, root gap, mismatch, angular distortion and final dimensions against drawing tolerances before welding and after cooling.

Instrument calibration: NDT equipment must be calibrated at defined intervals; calibration certificates must be traceable, and out-of-calibration equipment invalidates results.

Non-conformance handling: record the defect, raise a non-conformance report, decide repair or acceptance by concession, and re-inspect after repair with the same or extended NDT.

Inspection and test plan (ITP) defines hold points (work cannot proceed without witness) and witness points (notification required but work may proceed).

Visual testing (VT) detects surface-breaking and geometric defects; requires adequate illumination (typically at least 500 lux, higher for detailed inspection) and access.

Penetrant testing (PT) detects surface-breaking defects in non-porous materials; clean, apply penetrant, dwell, remove excess, apply developer, inspect under suitable light; fluorescent PT needs UV-A at about 365 nm.

Magnetic particle testing (MT) detects surface and near-surface defects in ferromagnetic materials only; defects best detected lie roughly perpendicular to the magnetic field lines; AC favours surface, DC favours subsurface.

Ultrasonic testing (UT) detects internal planar defects; uses a probe and couplant, with calibration blocks (V1, V2, or IIW blocks) and DAC/TCG curves; defect sizing by 6 dB drop or -20 dB technique.

Radiographic testing (RT) detects volumetric and internal defects; image quality indicator (IQI) wire or step-hole type verifies sensitivity; planar defects oriented parallel to the beam may be missed.

Acceptance levels: ISO 5817 defines quality levels B (stringent), C (intermediate) and D (moderate); ISO 11666 and ISO 10675 define UT/RT acceptance levels 2 and 3.

Defect types: porosity (rounded, gas), slag inclusions (linear, irregular), lack of fusion (planar, straight), lack of penetration (planar, at root), cracks (sharp, planar, most critical), undercut (toe groove).

Eddy current testing detects surface and near-surface defects in conductive materials; it is sensitive to cracks and conductivity changes but not suitable for thick-section internal defects.

Arc eye (photokeratitis) is caused by UV radiation; welding helmets must have a filter shade number matched to the process and current (for example, shade 10-13 for SMAW at 100-300 A).

Electric shock risk rises with wet conditions, high OCV and contact with the electrode; use low-voltage (VRD) devices where required, dry insulation and proper earthing.

Fume and gases: welding fume contains metal oxides and may include hexavalent chromium from stainless steel; use local exhaust ventilation and respiratory protection where exposure limits are exceeded.

Ozone and nitrogen oxides form in GTAW and plasma arcs, especially in confined spaces; ensure ventilation and gas monitoring before entry.

Fire and explosion: remove combustibles from the hot-work area (typically 10 m radius), use a fire watch, and obtain a hot-work permit; never weld near flammable gas or dust.

Confined space entry requires gas testing (oxygen about 19.5-23.5%, flammable gas, toxic gas), a permit, a standby person and rescue equipment.

Compressed gas cylinders: store upright, secure with chains, separate fuel and oxidiser, keep away from heat, and never use oil on oxygen fittings.

Noise, radiation and manual handling: arc welding can exceed 85 dB(A); use hearing protection, screen others from UV, and manage repetitive lifting and awkward postures.

ISO 3834 defines quality requirements for welding: parts 1-6 cover requirements, with part 2 (full), part 3 (standard) and part 4 (elementary) levels; selection depends on product criticality.

EN 1090-2 covers execution of steel structures; execution classes EXC1 to EXC4 set the required level of NDT, welder qualification and documentation.

ISO 9606-1 (steel) and ISO 9606-2 (aluminium) govern welder qualification; ISO 14732 covers welding operators for mechanised and automatic welding.

ISO 15614 series covers procedure qualification; ISO 15613 covers pre-production welding tests where standard test pieces are not representative.

Contract types: in a lump-sum contract the contractor bears quantity risk; in a remeasured contract payment follows measured quantities; in design-and-build the contractor takes design responsibility.

Liability: the contractor is generally responsible for workmanship and compliance with the specification; the client is responsible for design unless delegated; latent defects may remain actionable after acceptance.

Inspection authority: third-party inspection is independent of the fabricator; the inspector's role is verification, not supervision or instruction of the workforce.

Documentation: WPS, WPQR, welder certificates, material certificates (EN 10204 type 3.1 or 3.2), NDT reports and as-built drawings form the quality dossier handed over at completion.