IIW IWT common mistakes
IIW IWT · Understand the traps and how to avoid them.
When asked to identify a weld defect from a written description (e.g. 'linear indication along the fusion line, detected by UT, oriented parallel to the weld axis'), the candidate names the defect by its visual appearance rather than by the mechanism that produced it, so they confuse lack of fusion with lack of penetration or with a slag line.
Candidates learn defect names as a vocabulary list and never link each defect to its formation mechanism, its typical location in the joint, and the NDT method that best detects it. Under exam pressure the description is matched to the most familiar word rather than analysed.
What to do instead
Build a defect matrix with one row per defect (porosity, slag, lack of fusion, lack of penetration, undercut, crack types, spatter, burn-through) and columns for mechanism, usual location, most sensitive NDT method, and typical cause (current, travel speed, angle, gas, preparation). Practise reading a description and writing down the mechanism first, then deriving the name from the mechanism.
On heat-input and preheat questions the candidate quotes a formula but substitutes the wrong units, typically mixing mm and cm for plate thickness or using voltage in kV, and then reports a heat input that is out by an order of magnitude without noticing.
Heat input Q = k·U·I/v is simple enough to be memorised without unit discipline, and exam questions deliberately mix millimetres, centimetres and travel speed in mm/min or cm/min. Candidates also forget the efficiency factor k differs between processes (about 0.8 for SAW, 0.6–0.8 for GMAW, lower for TIG).
What to do instead
Always write the unit next to every substituted number and carry them through the calculation. Convert travel speed to mm/min and thickness to mm before computing, then sanity-check the answer against known ranges (typically 0.5–3 kJ/mm for arc welding). Do five worked examples per process with the efficiency factor stated.
The candidate treats the carbon equivalent as a single memorised threshold, answering 'preheat is needed above 0.4' regardless of the steel grade, thickness, hydrogen level or heat input stated in the question.
CEV and Pcm formulas (IIW, Ito–Bessyo) are often learned as one number, and candidates do not distinguish which formula applies to which steel family or how thickness and diffusible hydrogen shift the required preheat.
What to do instead
Learn both CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15 and Pcm, and know that Pcm is used for low-carbon micro-alloyed steels. Practise using a preheat chart with thickness and hydrogen level as axes, and state in your answer which variables you are holding constant.
When interpreting a radiograph or an ultrasonic indication described in text, the candidate judges acceptance purely on indication size and ignores the applicable acceptance level, the weld quality level, and whether the indication is planar or volumetric.
Candidates conflate 'large indication' with 'reject' and 'small indication' with 'accept', forgetting that planar indications such as cracks and lack of fusion are unacceptable at almost any size, while isolated porosity is judged against a level-dependent table.
What to do instead
For every acceptance question, first state the applicable standard and quality level, then classify the indication as planar or volumetric, then apply the size/length criteria. Memorise that cracks and lack of fusion are planar and generally rejectable, and practise comparing two indications of the same size but different type.
In welding procedure questions the candidate describes what a WPS contains but cannot explain the difference between pWPS, WPS, WPQR and welder qualification, or what a 'significant' versus 'non-significant' change to a qualified procedure requires.
The documents are learned as an alphabetical list rather than as a sequence of qualification logic, and the essential-variable concept is not connected to the reason requalification exists.
What to do instead
Draw the qualification chain: pWPS → procedure qualification test → WPQR (with test results) → WPS issued from it → welder/operator performance qualification, each with its own scope. Then list essential variables per process (e.g. for GMAW: transfer mode, current type, shielding gas family, position, thickness range) and mark which changes force requalification.
On residual stress and distortion questions the candidate lists all mitigation methods generically ('preheat, stress relief, sequencing') without matching the method to the specific distortion type or explaining the mechanism by which it reduces stress.
Distortion types (longitudinal shrinkage, transverse shrinkage, angular distortion, bowing, buckling) are studied separately from the remedies, so the answer becomes a memorised list rather than a reasoned selection.
What to do instead
For each distortion type, write the governing mechanism (non-uniform heating, shrinkage of the weld metal against restraint) and then the two or three remedies that act on that mechanism (balanced welding, backstep, preset, jigs, thermal stress relief, peening with its caveats). Practise justifying one remedy against another for a stated joint and restraint condition.
Health and safety answers name the hazard (fume, arc radiation, electric shock, gas cylinder) but omit the specific control measure and its technical basis, for example failing to distinguish extraction at source from general ventilation, or not knowing the voltage limits for working in wet or confined conditions.
Safety is revised last and from summary lists, so candidates recognise the hazard but cannot state the hierarchy of control or the numeric threshold the examiner is looking for.
What to do instead
For each hazard, prepare a three-line answer: hazard and route of exposure, primary engineering control, and the numeric limit or standard reference (e.g. OEL for welding fume constituents, no-load voltage limits, confined-space gas testing order). Learn the hierarchy of control and apply it explicitly in every answer.
The candidate answers a process-selection question by naming a favourite process rather than by weighing the stated constraints: material and thickness, position, required deposition rate, joint access, heat input limits, and available power supply.
Processes are revised in isolation, each with its own advantages list, and there is no framework for comparing them against a set of constraints, so the first plausible process is chosen.
What to do instead
Use a fixed comparison grid: thickness range, position capability, deposition rate, heat input, equipment and power needs, skill level, and applicable materials. Answer by eliminating processes that fail a hard constraint first, then comparing the survivors on the soft criteria stated in the question.
Welding metallurgy answers describe the general effect of cooling rate on microstructure but cannot connect a specific heat input and plate thickness to the resulting microstructure and property change in the heat-affected zone, or explain sensitisation and hydrogen cracking by mechanism.
Phase diagrams and CCT diagrams are memorised as pictures, not used as tools, and the candidate does not practise reading a CCT diagram to predict hardness for a given cooling time.
What to do instead
Practise the chain: heat input and thickness → cooling time t8/5 → position on the CCT diagram → microstructure → hardness and toughness → cracking risk. Do the same for sensitisation (chromium carbide precipitation at grain boundaries in the 450–850 °C range) and for hydrogen-assisted cold cracking (susceptible microstructure plus hydrogen plus restraint plus stress).
Practical and process-operation answers stay at textbook level: the candidate states the correct nominal parameter but cannot explain what the operator sees and does when the condition deviates, for example diagnosing porosity from gas flow, draught or contaminated base metal, or recognising wire feed problems from arc sound and spatter.
Practical knowledge is assumed rather than rehearsed, and candidates do not translate shop-floor troubleshooting into the structured cause-and-effect language the exam expects.
What to do instead
For each common problem (porosity, spatter, undercut, poor penetration, arc instability), write a symptom–cause–check–correct table covering gas, consumable, parameter, preparation and equipment. Rehearse explaining a diagnosis aloud in sequence: what is observed, what is ruled out, what is measured, what is changed.