Manufacturing Process Surveillance
Watch the process, not just the product
Surveillance is continuous verification that the supplier is doing what its own procedures and your PO require. Build the picture from incoming material records, first-piece or first-article inspection, in-process dimensional checks, welding controls (WPS/PQR, welder qualification and stamps, preheat and interpass limits), heat-treatment charts and furnace surveys, NDE personnel qualifications, PMI, coating controls, and the calibration status of every instrument in use. Traceability is the spine of this domain: from the finished part back to a heat number and mill test report, and forward again. Use the MTR to check grade, chemistry, mechanical properties and supplementary requirements, and confirm the heat numbers on the product, the test records, and the certificates all agree.
Traps: photocopied MTRs with no link to the actual heat, heat numbers that appear on paperwork but not on the parts, welders whose qualification range does not cover the thickness or process in use, a process change (new heat-treat cycle, new coating) made without re-qualification, and treating a certificate of conformance as objective evidence of anything.
Worked example: PMI on a duplex stainless flange shows chromium below the MTR value. Quarantine the lot, request re-verification by a second method, and treat it as a suspect mixed-material issue until proven otherwise. Rule of thumb: match, don't trust - every product to its heat, every instrument to a calibration sticker, every procedure to the revision actually in use.