Agreeing acceptance evidence before the job starts

1. What acceptance evidence means

Acceptance evidence is the proof, agreed before work starts, that an online valve job has done what it promised. For a passing valve, that proof is a seat-leak test under conditions both sides agreed in advance. Without it, the job ends in opinion, and opinions do not survive audits.

A pressure rise on the gauge, a quieter valve or fewer bubbles suggests improvement. None of these signs confirms it. Screening evidence points the way, and the confirming test closes the question.

Seat leakage is also the right thing to test. A risk-based valve integrity study of upstream and midstream sites, published by Valve World, found 61 per cent of valve failures in that population were passing valves. Distributions vary by plant and by valve population, so treat the figure as a signal rather than a rule.

2. Choosing the confirming test

The confirming test for a passing valve in the field is a seat-leak test under agreed conditions. Three forms are common in practice:

1. Pressure decay across the closed valve, measured over an agreed period.
2. Double block and bleed monitoring, where the line arrangement allows it.
3. A witnessed leak test, observed at a point you both agreed.

Agree the conditions as well as the method. Cover the test medium, the test pressure, the stabilisation period and the pass threshold. Write all four into the job scope before the crew leaves.

Be equally clear about standards. API 598 and ISO 5208 are factory acceptance references for seat leakage. A factory test certifies a valve leaving manufacture. A field test reports a worn valve in live service, and it should never be presented as an API 598 result. See what the API 598 criteria do and do not prove.

3. Witness, gates and permits

Name the witness before the job starts, and agree who signs the final entry. A witness from your operations or inspection team gives the result weight in an audit later. The witness does not run the test. They watch it run, and they sign what they saw.

Confirm the gates that make the work possible at the same time. The injection fittings must be in good condition. The valve design and the service must suit injection treatment. Site rules and the permit-to-work must allow work on a live, pressurised line. Where the maker's documentation exists, consult it for limits and warranty terms.

If a gate fails, the honest answer is to stop and reassess, not to stretch the criteria. Some valves cannot be treated in service, and no agreed test changes that fact. Agree the same witness for any repeat test, so results stay comparable.

4. Records agreed before mobilisation

The record is the deliverable, so agree its shape before the crew arrives. A per-valve entry should carry at least the following:

1. Valve identity: tag number, size, class and service.
2. Condition before treatment, including the screening signs observed.
3. What was injected, in controlled amounts within equipment and fitting ratings.
4. The pressure response during injection, and any stop-work decision.
5. The agreed test, its conditions, its result and the witness signature.

This is what turns a visit into evidence. Our field teams record each valve this way on clean, lubricate and seal work. For the document itself, see the service record you receive after each valve. The stages that feed it are described under online sealant injection and acceptance evidence.

Also agree who holds the signed record, and how copies reach your files.

5. No over-claiming on either side

A pass means the valve met the agreed test on the day, under the agreed conditions. It is not a promise about next year, and it should not be written as one. Seats degrade with wear, dirty service and ageing sealant, and an honest record says so.

The same honesty applies to failure. If the valve does not pass after treatment, the endpoint is a proper assessment, repair or replacement. Repeating injection until a gauge pleases you is not an offer anyone should make.

Put all of this in writing when choosing an online valve maintenance provider. Our guide to writing an RFQ for online valve maintenance shows where acceptance criteria sit in the scope. A clear criterion also protects the provider, because it stops a defined test drifting into a vague promise.