Most valve failures in service are not exotic. They come from a seat pocket that was not concentric with the stem bore, a flange facing that was cut in a second setup, a test that was signed before the hold time elapsed, or a certificate that does not actually belong to the body it is stapled to. This page describes what we do about each of those.
Machining
Bodies and bonnets are machined on CNC lathes and machining centres. Where the geometry allows, the seat pocket, the stem bore and the bonnet joint are taken in one setup so the relationship between them does not depend on how well a fixture was reset. Flange facings are cut to the serration and finish the dimensional standard calls for, because a facing that is too smooth will not hold a spiral wound gasket any better than one that is too rough.
Dimensional checks
Face-to-face, flange bolt circle, bore, seat diameter and stem bore concentricity are measured against the drawing and recorded. Face-to-face is checked on every body rather than on a sample, because it is the one dimension that decides whether a replacement valve drops into an existing line.
Pressure testing
Shell test, then backseat where the design has one, then seat test in both directions on bidirectional valves. Test pressures and hold times follow the practice described in API 598 for the class and size. The bench record carries the body serial number, the pressures applied, the hold time and the result, and it is retained rather than discarded once the valve ships.
Material traceability
Every pressure-retaining part carries the heat number of the casting or forging it came from, stamped or hard marked, and that number follows the part through machining and assembly onto the material certificate that ships with the valve. Trim material is recorded separately from the body, since it is usually the trim that has to be matched when a valve is repaired years later.
Assembly and painting
Assembly happens after test, not before, so a valve is never painted over a joint that has not been proved. Bolting is torqued to the value on the assembly sheet in a recorded sequence. External protection is specified from the installed environment, which for a buried or offshore valve is a different answer from a valve in a covered plant room.
Spares and repair
Seats, seals, gaskets and stems are held for the models currently in production. A repair kit is identified from the body serial number rather than from a model name, because the same model can carry more than one trim combination.
[Client to confirm the machine list, in-house inspection equipment, and any third-party witnessed testing or approvals actually available, before this page is published.]