The Difference Between Quality Assurance (QA) and Quality Control (QC)

There is often a lack of understanding when it comes to the difference between Quality Assurance (QA) and Quality Control (QC).  The terms are sometimes used interchangeably, however; they are very distinct in their activities and meaning.  This blog provides a bit of background about what quality is, discusses processes, and used a diagram to define QA and QC.  Industrial megaprojects serve as the backdrop for discussions.

Quality in Project Management

Quality is achieved when a work output meets the needs of its intended recipient.  Needs are a combination of implied or explicit targets and are typically referred to as requirements. Requirements are defined by the output recipient, not by the person preparing the output.  In industrial projects, the engineering targets are defined by the project’s business case while vendor and construction requirements are defined by the engineered drawings and specifications.  Then further an output is from meeting requirements, the lower its quality.

Achieving Quality

Achieving quality in any manufacturing, project, or other setting involves developing and following processes.  Processes are a defined set of steps that result in a work output.  Repeated use of a process should result in identical outputs.  When processes are written down, they are known as procedures (higher level) or work instructions (task level).  If good processes are followed, the result should be outputs that consistently meet requirements.  This is why ISO 9001, TQM, and all other sound quality systems are based on the process approach.

Quality Assurance and Quality Control Definitions

In industrial projects, a Quality Management System (QMS) is typically implemented to oversee quality of the facility during design and construction.  It is critical to implement the QMS right from the project outset.   QA and QC are the core elements of the QMS.  QA is a check of the work process to make sure it is being followed while QC is an inspection and / or test that verifies the process output is correct (see Figure 1).  

Quality Assurance Process

The only assurance of quality is following a sound process.  QA typically involves audits, managing Inspection and Test Plan (ITP) development, and using the NCR, root cause, and other quality assurance processes.  The QA team is also typically involved in process-related training course development and delivery.  The goal of the QA team is to improve processes so that they are more reliable in their delivery of quality outputs.

Implementing QA right from the outset reduces the likelihood that a project will have significant rework during the construction phase.  If the work process is not followed or is flawed, the likelihood that the output will be correct is very small – mostly luck.  All it takes is one step in the process to be floundering for major problems to appear later on.  Developing a sound quality plan and ensuring that the various teams are aligned with the plan is an excellent start to the QA function.  Following this up with a strong auditing program provides you with assurance that teams are likely going to deliver an acceptable output. 

Fit For Purpose In Major Industrial Projects

Quality Control

QC is focused on inspections, tests, and completing the Inspection and Test Records (ITRs) required by the ITP.  The completed ITP will be a key document in any industrial project’s turnover when the work is complete.  QC documentation is provided to the QA team for review.  QA monitors trends and notes made by QC inspectors to gain insight into how well a process is functioning.  It is not feasible to inspect/test all aspects of a project and only a very small percentage of any completed work is subject to QC.

Industrial projects often have trouble because they are focused on QC checks of the finished construction and have little – if any – QA.  Focusing on QC can result in massive cost overruns and schedule delays due to ongoing rework (unfortunately rework is like a sasquatch and rarely documented….).  Deficient work is often not noticed until later in the project when it is joined to another component – leading to a high level of rework and major cost and schedule overruns.

What is the difference between a process, procedure, and work instruction? 

A process is a repeated set of steps that are followed when performing a task.  Procedures and work instructions are processes that has been written down in an instruction-based format.  A procedure is often a higher-level document that calls on tasks in order of use while work instructions contain precise steps on how to perform a task.

What is QA/QC? 

QA refers to quality assurance.  QC refers to quality control.  QA is process-focused since the only assurance of quality is that a process is being followed.  QC is focused on inspection and testing of outputs to ensure they meet relevant requirements.  QC is a part of most QA programs.

What is a Quality Management System (QMS)?  

A QMS is a system that is developed to ensure that work outputs from anywhere within an organization meet the receiver’s requirements. A QMS includes QA, QC, and often overlaps with training.

What is rework? 

When an output does not meet requirements, it may be reworked to correct the deficiency.  Rework may involve repairing or replacing the deficient component.

What is a quality plan? 

Quality plans are used in projects to document how a project team will ensure the quality of the end-product.  They should define the approach to QA, QC, and quality-related training that will be provided to project participants.


QA and QC are components of a strong QMS.  QA supports the process approach to work and works to resolve issues with and improve processes.  QC is output-focused and inspects and tests a small percentage of the completed work.  QA works to resolve non-conforming work before it happens by fixing process issues while QC identifies and reworks non-conforming work after it has been completed.  QA has a high return on investment and can reduce a reliance on QC.

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