QC - Quality Control
So Piping QC is controlling the quality of piping.
I’ll define piping as fabricated assemblies of components such as pipe, elbows, tees, flanges and other fittings, as that’s my area. The principle applies to manufacture of these components at a pipe mill or forge, but the example below might not be valid.
A piping fabricator in the process / power industries has to follow some form of standard like the ASME B31 series, AS 4041 here in Australia.
To assure the purchaser that they are following the standards correctly, they set up QA systems which are also set out by standards - The ASME standards tend to set out the QA requirements themselves, whereas here in OZ, the fabricator follows AS/NZS/ISO 9001 to develop a quality management system.
So QA (quality assurance) is the set of procedures or rules you implement to achieve a product which conforms to an application standard. QA covers the development of work instructions, record keeping templates etc (ITPs, WPS, Hydro test forms). QA aims to direct fabricators and inspectors how work is to be conducted and checked at various stages)
QC is then the step where items are QA templates are filled in by fabricators (boiler makers, pipe fitters, welders) and reviewed / checked against the actual part and code requirements by inspectors or supervisors. At the QC step, items which do not meet the application standard are placed on hold. They will either be scrapped or repaired.
John is conducting a hydrotest on a pipe spool. He is given the QA form which has been completed by the foreman or project engineer. The QA form tells John that the test parameters are 2000 kPa for 30 minutes.
John’s new so he’s also given a copy of the hydrostatic test work instruction (part of the documented QA system). He reads that he needs two calibrated gauges that will provide for the test pressure to be within the middle third of the scale under test conditions so he goes to the storeman and asays “I need two gauges, they can be between 3000 kPa and 6000 kPa”. He gets two gauges.
He assembles the test equipment following the safety requirements and applies pressure, then isolates the pump from the assembly. He checks the two gauges and writes the starting test pressure down On the QA form. He waits 30 min (filling in some extra details on the form and checking the test spool for leaks etc.) He writes the final pressure down on the form and signs it. He releases the test water and cleans the item up ready for packaging.
The form is now a record of quality control (QC). It’s given to the supervisor, project engineer or quality department for inclusion in the dossier. But Fred the inspector reviews these documents and countersigns them before filing or issuing them. He notices that one of the gauges has not been calibrated within the time frame specified in the QA procedures. He puts the pipe spool on hold, tracks down the suspect gauge takes it out of service and finds John to tell him he has to do the test again with calibrated gauges. Fred also has to deal with getting the gauge calibrated and determining whether there needs to be an incident report.
So QA is how you plan to monitor quality (by setting out a formal system of responsibilities, checks and outcomes), while QC is what you do each day to provide proof that you’re monitoring quality.