Preventive valve maintenance: 5 mistakes to avoid

Preventive maintenance on industrial valves usually fails for the same five reasons: applying a single interval to the whole valve population, not recording set-pressure history, testing the set pressure without a calibrated bench, ignoring the surrounding installation, and fitting non-equivalent spare parts. Fixing these five points extends valve service life and prevents most unplanned shutdowns.

Mistake 1 — Applying the same interval to every valve

Valves do not degrade at the same rate. A safety valve on clean steam can hold its set pressure for years, while the same valve on a fluid carrying solids, or on polymerising or corrosive media, loses tightness in months. Recommended practice (API 510 and API 576) is to start from a base interval — around 5 years for clean services and 1 year for severe ones — and then adjust it with the actual result of each inspection. A criticality-based plan, rather than a calendar-based one, cuts unnecessary interventions and concentrates effort where the risk is.

Mistake 2 — Not recording set-pressure history

Every pop test returns one valuable figure: the actual opening pressure before the valve is touched (as-found). Comparing that value with the nominal set pressure across successive overhauls shows the drift of the equipment and lets you anticipate failure. Without that history there is no objective way to lengthen or shorten the interval, and the decision ends up being made on intuition.

Mistake 3 — Testing the set pressure without a calibrated bench

Checking the set pressure with process pressure, or with a gauge that has no traceability, is not a test — it is an estimate. The test must be run on a calibrated bench, with the fluid appropriate to the service, and must end with a seal and a set-pressure certificate. That certificate is what proves to an inspector that the valve really protects the equipment at the declared pressure.

Mistake 4 — Ignoring the surrounding installation

A perfect valve on a poor line still fails. The most common problem points: inlet line pressure drop above 3 % of the set pressure — the threshold API 520 associates with chattering —, excessive back pressure in the discharge header once new equipment is added, discharge lines with no drainage that collect condensate, and upstream rupture discs whose burst indicator nobody monitors.

Mistake 5 — Fitting non-equivalent spare parts

A spring, a seat or a gasket from a different source changes how the valve behaves and, above all, voids its certification. After replacing components with non-equivalent ones, the certified capacity and the marking (PED 2014/68/EU, ATEX 2014/34/EU where applicable) are no longer valid, even if the valve appears to work.

How to build a plan that works

1. Inventory every valve with its criticality, service and set pressure.
2. Set a base interval per service type and adjust it with the as-found results.
3. Always test on a calibrated bench and file the set-pressure certificate.
4. Check the inlet line, the back pressure and the drains at every intervention.
5. Use manufacturer spare parts only, and document every replacement.

Tecnovent overhauls, sets and certifies safety valves and protection equipment for tanks and process plants. If you need to audit your maintenance plan or rebuild your plant's set-pressure history, contact our technical team.