Review this article about vendor inspection procedures and applications.
This article provides you with information about the second party or third party inspection process in manufacturing shops. This article also provides lots of other links for shop inspection practices for each equipment type.
Assume an oil company orders manufacturing of several pumps from a pump manufacturer.
So there will be a proforma invoice (PI) and a purchase order (PO). The PI is issued by the pump manufacturer, with detailed pump specifications and prices, and at the same time, a PO will be issued by the oil company, which stats its agreement with the specifications, prices, and ordering for the manufacturing of the pumps.
PI and PO are important commercial documents.
Before the start of the manufacturing process, the oil company will agree with the pump manufacturer for the inspection process. Normally, this process will be done based on the agreed upon inspection and test plan.
For more details, review the Inspection and Test Plan article.
In this important document, the inspection “hold” and “witness” points will be determined, and it will be necessary for the pump manufacturer to notify the oil company inspector for such inspection in advance.
Assume the “inspection and test plan” determine 5 inspection points in the manufacturing process, such as material certificate review and identification, casing hydro static testing, impeller balancing, performance test and run-out test.
So when the manufacturer reaches to these points, it must notify the oil company inspector (in advance) to come for the inspection and testing. Finally, if the result of inspection visits were satisfactory, then the inspector will issue the inspection release note.
This oil company has several options to designate an inspector as follows:
Please note that most of the clients such as this oil company mandate the engineering company to hire a third party inspection agency.
Using the “inspector” wording for the engineering company's personnel and the name of inspection department in the engineering company are not correct. They must be called the and must be quality control department. But some engineering companies call their quality control department an inspection department.
Inspector can only be used for someone who is the purchaser's employee or the purchaser's designated person working in the inspection agency.
When the inspection is carried out in the manufacturing shop, it is called shop inspection.
The 3rd Party Shop Inspection article provides you some more supplementary information regarding this subject.