Construction and design
The exam tests joint and weld design, symbol interpretation to ISO 2553, and static versus fatigue assessment - and whether you know the difference between specified and achieved throat.
Core rules
- ISO 2553: solid reference line means the weld is on the arrow side; dashed line means the other side. Supplementary symbols cover all-around, field weld and surface finish. System A and System B place dimensions differently.
- Fillet throat a = z · cos 45° = 0.707 z for a 90° joint. Design resistance is calculated on throat, not leg.
- Partial-penetration butt welds require an explicitly specified penetration; without back gouging or backing, full penetration cannot be assumed.
- Fatigue design to EN 1993-1-9 uses detail categories: a category 80 detail accepts 80 MPa stress range at 2 million cycles. Toe geometry and ISO 5817 quality drive the category.
- Static fillet design to EN 1993-1-8 checks resultant throat stress against design shear strength.
Worked example
A T-joint needs a design throat of 6 mm. Leg z = 6 / 0.707 = 8.49 mm, so specify 9 mm. If the fabricator delivers an 8 mm leg, a = 5.66 mm - about 6 % loss of throat and capacity, although the leg is only 1 mm short. This is why drawings state a and inspectors gauge a rather than z.
Traps
Measuring leg and calling it throat; misreading which side of the reference line carries the weld; assuming an arrow-side symbol means both sides; forgetting that ISO 13920 tolerance permits leg variation that must still satisfy minimum throat.