ISO 5208 leakage rates: reading the classes

1. What an ISO 5208 class means

ISO 5208 gives a class-based framework for valve leakage-rate acceptance. The class belongs with the related test requirements, not as a free-standing product claim.

Read the class as a test result within a stated basis. It is not a general promise that the valve will remain unchanged.

The applicable standard text should settle the exact requirement. Operators typically keep the class, valve identity, test basis and result together.

Our valve integrity management guide places this acceptance record beside later inspection and maintenance evidence.

2. Read the class with its test record

A class name alone leaves important questions unanswered. The useful record connects the label to the tested valve and accepted result.

1. Check that the valve identity matches the test record.
2. Confirm that ISO 5208 is the stated test basis.
3. Keep the class exactly as the record reports it.
4. Retain the relevant test conditions and accepted result.
5. Record any later field test as separate evidence.

This discipline prevents class labels moving between different valves or tests. It also stops a short catalogue statement replacing the underlying acceptance record.

The API 598 guide explains why its allowable leakage criteria should not be renamed as ISO classes.

3. Relationship with API 598

ISO 5208 and API 598 both concern valve leakage testing. Their acceptance structures are not interchangeable labels.

ISO 5208 defines leakage-rate classes and corresponding test requirements. API 598 provides valve inspection, pressure-testing and allowable leakage criteria.

Therefore, an API 598 pass is not automatically an ISO 5208 class. A claimed class needs a stated ISO 5208 basis and supporting record.

When records conflict or omit the test basis, keep the result unresolved. The standard text, purchaser requirements and responsible engineering review should settle it.

4. What the class does not prove in service

Factory acceptance records condition during a controlled test. An installed valve later faces storage effects, installation, contamination, movement and service history.

A class does not prove that the valve closes fully today. It also does not set one maintenance or exercise interval for every application.

Pressure rise, noise and continuing flow can suggest seat leakage. They remain screening evidence until a suitable field test confirms the installed condition.

The passing valves guide covers this diagnosis boundary. The ASME B31.8 article explains how operators build defensible intervals.

5. Use class data in a maintenance programme

Operators typically preserve the factory class as baseline evidence. They then add inspections, field tests, movement history and maintenance findings over time.

Do not describe a changed valve as still meeting its old class without suitable evidence. State the current finding and the method used.

Where treatment is proposed, check the gates first. Injection fittings must be sound, design and service must suit injection, OEM guidance applies, and operations must permit work.

Our field services support valve surveys, controlled treatment and retesting. The engineering endpoint may still be isolation, internal assessment, repair or replacement.