In the context of Non-Destructive Testing (NDT) for welding and metalworking, the
distinction between Quality Control (QC) and Quality Assurance (QA) still holds, but it is
more focused on the methods and tools used to ensure the components are defect free.
Quality Control (QC) in NDT:
Definition: In Quality Control, NDT is used as a tool for detecting defects in the finished or
in-progress metal components. QC’s primary goal is to identify any flaws or irregularities
that might affect the structural integrity or performance of the product.
Purpose: NDT methods in QC are performed after or during production to verify the quality
of individual parts and ensure they meet design specifications. However, as the name
suggests these non-destructive methods ensure that the components are not affected in the
process.
Examples include methods such as ultrasonic testing (UT), magnetic particle testing
(MT), radiographic testing (RT), and dye penetrant testing (PT) used to detect cracks,
voids, weld defects, and other structural issues. Further elaborating:
Ultrasonic Testing (UT): Checks for internal flaws like cracks or voids in a metal
part.
Radiographic Testing (RT): Using X-ray or gamma-ray inspection examines welds
or metal structures for internal defects and fractures.
Magnetic Particle Testing (MT): Detects surface or near-surface (shallow) cracks in
ferromagnetic materials.
These tests help identify any deviations from the required standards or specifications, so that
timely corrective action – like reworking or scrapping parts – can be conducted.
Quality Assurance (QA) in NDT:
Definition: Quality Assurance in NDT is rather about ensuring that the NDT processes,
techniques, and equipment are applied correctly and consistently throughout production to
ensure that defects are properly detected while simultaneously reducing false positives and
eliminating chances of false negatives.
Purpose: QA focuses on setting up systems and procedures to ensure the NDT
processes are applied effectively and accurately, reducing the likelihood of defects slipping
through undetected and subsequently unaddressed.
Examples:
Establishing standards for NDT procedures, involving creating and maintaining
guidelines for how inspections should be carried out at different stages of production.
Training and certifying NDT technicians, ensuring that personnel are trained and certified
(e.g., by ASNT or other industry bodies) to perform necessary tests and handle the
equipment.
Calibrating equipment regularly, ensuring that testing equipment, such as ultrasonic
devices or X-ray machines, is regularly calibrated and used with the right apparatus and
consumables.
Process documentation, ensuring that all NDT results are documented for traceability and
review, establishing a system to identify trends or recurring issues that could indicate
systemic problems in production processes.
Key Difference in NDT:
- QC in NDT involves inspecting the components after or during production using
non-destructive testing methods to identify defects affecting the product performance. - QA in NDT involves ensuring proper inspection and reporting by maintaining
quality procedures, training, calibration, and systematizing the NDT processes.
In metalworking, both QC and QA with NDT work simultaneously to ensure structural
integrity of the final product without damaging the components in the process.
