A rejected valve on site is rarely a manufacturing defect. Far more often it is a perfectly good valve built to a specification that did not describe the actual service. Every one of the mismatches below is cheap to prevent at requisition stage and expensive to discover at installation.
1. Pressure class chosen from line pressure alone
Class rating has to account for design temperature, not just design pressure. The pressure-temperature rating curve derates significantly at elevated temperature, and a class selected from operating pressure at ambient will be undersized in hot service.
2. Flange face type mismatch
Raised face against ring type joint is the classic site surprise. Confirm face type, finish and gasket specification on both mating flanges, and confirm them against the isometric rather than against memory of the rest of the line.
3. Trim metallurgy that ignores the fluid
Standard trim in sour, chloride-bearing or high-velocity erosive service fails early. Where hydrogen sulphide is present, NACE MR0175 compliance is a hard requirement, not an upgrade option.
4. Face-to-face dimension assumed
A valve that meets every functional requirement but is fifty millimetres longer than the gap in the spool will not be installed that day. Confirm the applicable face-to-face standard and the specific dimension for the size and class.
5. Actuator interface and fail position undefined
- Mounting standard and stem interface confirmed against the actuator, not assumed.
- Fail-safe position stated explicitly: fail open, fail closed or fail in place.
- Supply medium, supply pressure and control signal specified.
- Area classification and ingress protection rating matched to the installation.
6. Testing and certification left vague
State the required test standard, the acceptance criteria and whether witnessed inspection is needed before shipment. A certification package requested after delivery is a package that may not exist.
7. Spares not ordered with the valve
Seal kits and trim spares ordered at the same time as the valve cost a fraction of what they cost as an emergency order eighteen months later, and they arrive with matching traceability.
PMA NRG reviews specifications with clients before the purchase order is issued, because a thirty-minute technical review routinely saves weeks of schedule.
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