On most industrial projects, “QA/QC” is written as if it were a single thing. In practice, quality assurance and quality control do different jobs, are done at different times, and fail in different ways. A project can have excellent inspectors and still produce defects if the system behind them is weak, and a project can have a perfect quality manual that nobody follows. So what is the difference between QA and QC? Here are clear definitions, examples and how they work together, for project managers, engineers and anyone new to industrial quality management.
What is quality assurance?
Quality assurance (QA) is the set of planned, systematic activities that make sure the right processes, qualifications and controls are in place so that work can be done correctly. It is preventive and process-focused: it asks whether the system will produce the right result.
What is quality control?
Quality control (QC) is the inspection, testing and checking of actual work and products against requirements, to find and correct defects. It is detective and product-focused: it asks whether this item, weld or joint meets the specification.
QA and QC side by side
| Aspect | Quality assurance | Quality control |
|---|---|---|
| Focus | Processes and systems | Products and work |
| Purpose | Prevent defects | Find and correct defects |
| Timing | Before and throughout the work | During and after the work |
| Typical activities | Quality plans, procedures, qualifications, audits, training | Inspections, tests, measurements, NDT |
| Typical outputs | Approved procedures, audit reports, qualification records | Inspection reports, test certificates, NCRs |
| Typical roles | QA manager, quality engineers, auditors | QC inspectors, NDT technicians, test engineers |
Examples from an industrial project
Welding
QA makes sure welding procedures are qualified, welders are tested and certified, and consumables are stored correctly. QC inspects fit-up, watches parameters, examines finished welds and reviews NDT results.
Concrete
QA approves the mix design and the testing laboratory. QC checks slump, takes test samples, checks reinforcement before pouring and reviews strength results.
Documentation
QA defines the dossier structure and record requirements. QC fills them with signed inspection and test records.
How QA and QC work together
QA sets up the system that QC works within. QC findings then feed back into QA. If inspections keep finding the same defect, QA should ask why: is the procedure unclear, is training missing, is a supplier unreliable? That feedback loop is where quality improves. A project with only QC keeps catching the same problems. A project with only QA has no evidence that its system works.
The full set of QA/QC activities on construction projects is described in QA/QC services for industrial construction projects, and the planning document that links them in inspection and test plans for industrial construction. For a map of inspection services from vendor shops to plant shutdowns, see industrial inspection and quality assurance services.
A simple test for any quality activity
Ask whether the activity checks a specific piece of work or the way work is done. Inspecting a weld, testing a cable or measuring a foundation is QC. Qualifying a procedure, training an inspector or auditing whether ITPs are followed is QA. Most project quality problems sit in the gap between the two, where a system exists on paper but nobody checks that it is working in the field.
Common confusions
- Treating QA as paperwork. Good QA prevents defects; manuals and audits are only its visible part.
- Treating QC as the contractor’s problem only. Owners also perform verification and witness inspections.
- Expecting QC to create quality. Inspection finds defects; it does not prevent them on its own.
- Using the same person for both without independence. Auditing your own inspection work weakens both functions.
Roles and careers
QA roles lean toward systems, audits and procedures, while QC roles lean toward hands-on inspection and testing. Many professionals move between them over a career. Why qualified people matter in both is discussed in why qualified QA/QC personnel matter on industrial projects.
QA/QC support from Apex Core Engineering
Apex Core Engineering supplies QA managers, quality engineers and QC inspectors for industrial projects and works within ISO 9001-certified quality management, alongside ISO 14001 and ISO 45001, as listed on its certifications page. It also places quality professionals through its manpower selection services.
Frequently asked questions
Is QA more important than QC?
Neither works well alone. QA prevents defects through the system, and QC proves whether the system worked on actual work.
Who is responsible for QA on a construction project?
Usually the contractor’s QA manager for its own system, with the owner auditing and setting requirements.
Is an inspector part of QA or QC?
An inspector who checks work against specifications is performing QC. Auditing whether procedures are followed is a QA activity.
Why are QA and QC written together?
Because they are closely linked and often managed by one department, even though their purposes differ.
Discuss QA/QC staffing with Apex Core Engineering.