IIW IWS common mistakes
IIW IWS · Understand the traps and how to avoid them.
When asked to choose a welding process for a given joint, material thickness and production volume, the candidate picks the process they personally use rather than matching process capability (penetration, deposition rate, heat input, positional ability) to the stated constraints.
Candidates prepare from practical experience and memorise 'their' process parameters; they do not build a comparison table of the IIW process families (SMAW, GMAW, GTAW, SAW, FCAW, resistance, laser, friction stir) against thickness range, position, and productivity, so the selection question becomes a preference question.
What to do instead
Build a one-page matrix with processes as rows and columns for typical thickness range, positions, deposition rate, heat input, filler requirement and typical applications. Practise 20 short scenario questions where you must justify the choice in one sentence citing two matrix columns.
The candidate explains a CCT or continuous-cooling diagram by reading the final microstructure only, ignoring that the answer depends on cooling time t8/5 and the steel's hardenability; they then predict hardness incorrectly for thick sections.
Diagrams are studied as static pictures rather than as a function of cooling rate. Candidates forget that t8/5 scales with heat input, preheat and plate thickness, so they cannot connect a change in welding parameters to a shift on the diagram.
What to do instead
For three heat inputs (e.g. 0.5, 1.5, 3.5 kJ/mm) sketch where t8/5 falls on a CCT diagram for a given steel, then state the resulting microstructure and approximate hardness. Repeat with preheat added and write the t8/5 formula from memory each time.
In construction-and-design questions the candidate sizes a fillet weld by matching the leg length to the load, forgetting that design throat thickness is 0.7 times the leg for equal-leg fillets and that the directional method uses different stress components than the simplified method.
Practical shop habit equates leg size with capacity. Candidates also mix the simplified and directional methods of weld design, applying partial safety factors from one method to the other, so the arithmetic looks right but the basis is wrong.
What to do instead
Work through five fillet-weld capacity problems twice, once with the simplified method and once with the directional method, writing the formula and each partial factor explicitly. Keep a card listing throat = 0.7 × leg, the resistance terms, and which standard clause each method comes from.
The candidate treats a welding procedure qualification as automatically covering a different material group, thickness outside the qualified range, or a change of consumable, without checking the essential and non-essential variable rules.
Candidates memorise that 'a WPS is qualified by a PQR' but never learn the variable tables, so they assume qualification transfers broadly. They also confuse procedure qualification with welder performance qualification, which have different validity ranges.
What to do instead
Create a two-column list: essential variables (material group, thickness, consumable classification, position, heat input) versus non-essential ones, and mark which require requalification. Then answer ten 'is a new qualification needed?' scenarios by citing the specific variable that changed.
When interpreting a radiograph or an ultrasonic indication the candidate names the defect from its appearance alone, without cross-checking position, orientation and the welding process that produced it, so slag is called lack of fusion and porosity is called a crack.
Defect recognition is learned from image galleries without the reasoning chain. Candidates do not systematically ask: where is it in the thickness, what is its orientation relative to the fusion face, is it linear or rounded, and which process and position would produce it.
What to do instead
For each defect class write a three-line signature: position in section, orientation, and typical cause by process. Then describe ten indications in words only (no images) and identify them from the signature, stating which second NDT method would confirm the call.
In health and safety questions the candidate lists engineering controls but omits the exposure assessment step, or states that fume extraction 'removes the hazard' without specifying capture velocity, extraction position relative to the arc, and the difference between local exhaust ventilation and general dilution.
Safety content is often revised as a list of hazards rather than as a hierarchy of controls with measurable performance. Candidates do not link the control to the substance (manganese, hexavalent chromium, ozone from GTAW) or to the monitoring method.
What to do instead
For three processes write the principal fume constituents, the applicable exposure limit concept, the extraction type and its capture velocity, and the respiratory protection level that remains if extraction is inadequate. Practise stating the hierarchy of controls in order with one welding example per level.
The candidate answers practical process-operation questions with nominal parameter values from a textbook and does not adjust for position, joint preparation, root gap or machine characteristic, so the stated current and voltage would not produce the described bead.
Parameters are memorised as single numbers instead of ranges tied to conditions. Candidates also ignore the relationship between wire-feed speed, current and voltage in GMAW, and between arc length and voltage, so their answers are internally inconsistent.
What to do instead
For GMAW, GTAW and SMAW write a parameter table with ranges for flat, vertical and overhead positions and the direction of adjustment when the bead is too convex, too concave or lacks fusion. Check internal consistency: does the stated voltage match the arc length described?
In supervision and planning questions the candidate calculates welding cost from labour and consumable price only, omitting deposition efficiency, duty cycle, rework allowance and the cost of preparation and NDT.
Costing is revised as a formula rather than as a production model. Candidates forget that operating factor and deposition efficiency change the effective arc time, and they treat rework as negligible when it is a major cost driver in quality-critical work.
What to do instead
Build one worked cost model for a butt weld: arc time from deposition rate and deposit mass, operating factor, consumable and power cost, preparation and NDT, plus a rework percentage. Then vary one input at a time and state which input dominates the total.
The candidate answers distortion-control questions by naming a single remedy (for example 'weld symmetrically') without matching the remedy to the distortion type: longitudinal shrinkage, transverse shrinkage, angular distortion, bowing or buckling each need a different measure.
Distortion is learned as a list of techniques rather than as a consequence of non-uniform heating and shrinkage. Candidates cannot map a mechanism to a control, so they offer backstep welding for a problem that needs balanced sequence or presetting.
What to do instead
Make a table of distortion type, mechanism, and the two most effective controls, including presetting, balancing, backstep, reduced heat input, and jigging. For five described fabrications name the likely distortion type and the control you would specify first, with the reason.
When a question asks for acceptance or rejection against a quality level, the candidate gives a verdict without stating the acceptance criterion, the NDT method and the extent of testing that the verdict depends on.
Candidates treat acceptance as a visual judgement. They do not recall that acceptance levels differ by NDT method and quality level, and that a verdict is only valid for the inspected volume and the specified technique.
What to do instead
For each defect type write the acceptance criterion at two quality levels and the method that detects it. Then answer ten 'accept or reject' prompts in the form: criterion, method, extent, verdict. If any element is unknown, state that the verdict cannot be given.