Inspection, testing and quality assurance
Inspection, testing and quality assurance tests whether you can choose the right test, read the acceptance level and place both inside a quality system - not whether you can operate the equipment.
Methods and capability
- VT (ISO 17637): surface, profile, undercut, misalignment; always first.
- PT: surface-breaking flaws in any material; needs a clean, dry surface.
- MT: surface and near-surface flaws in ferromagnetic steel; not for austenitic stainless.
- UT: volumetric, sensitive to planar flaws such as lack of fusion and cracks; needs roughly ≥8 mm thickness and access.
- RT: volumetric, good for porosity and slag; less reliable for planar flaws oriented parallel to the beam and needs radiation controls.
Standards and acceptance
ISO 17635 links material, thickness and quality level to the method. ISO 5817 defines quality levels B (stringent), C (intermediate) and D (moderate). NDT acceptance levels are separate: ISO 11666 levels 2 and 3 for UT, ISO 17636 class A/B for RT. Quality level B does not automatically mean UT level 2 - the contract and ISO 17635 decide.
Quality assurance
EN ISO 3834-2 to -4 set requirements from comprehensive to elementary. WPS are qualified by ISO 15614-1, welders by ISO 9606, NDT staff by ISO 9712. Records, calibration and nonconformance control are the auditable evidence.
Worked example
A 20 mm C-Mn butt weld with a B quality requirement. UT per ISO 17635 is selected because planar lack of fusion is the credible defect and RT is weak for it at that thickness. The UT acceptance level must be stated in the specification, and VT is still performed first.
Traps
Assuming RT finds all lack of fusion; using MT on stainless; treating ISO 5817 levels as NDT acceptance levels; forgetting personnel certification and equipment calibration.