ISO 5208 (Industrial Valves; Pressure Testing of Metallic Valves) is the international standard for factory pressure testing of industrial valves. It defines shell test pressures, closure test pressures, test durations, and a graduated system of leakage rates (Rate A through Rate G) that allow buyers to specify the exact tightness level required for their application. ISO 5208 is the international counterpart to API 598.
When ISO 5208 Applies
ISO 5208 is referenced in European and international valve procurement specifications (EN, DIN, BS standards). Oil and gas projects that follow EN standards, European clients, and international EPC contractors commonly specify ISO 5208 for gate, globe, check, ball, butterfly, and plug valves.
Test Types
| Test | Medium | Pressure | Purpose |
|---|
| Shell test | Water (liquid) | 1.5x maximum allowable pressure (PN x factor) | Body, bonnet, and joint integrity |
| High-pressure closure test | Water (liquid) | 1.1x maximum allowable pressure | Seat tightness under high differential |
| Low-pressure closure test | Air or nitrogen (gas) | 0.6 bar (typical) | Seat tightness under low differential |
Leakage Rates
The key feature of ISO 5208 is its graduated leakage rate system. Instead of a single pass/fail criterion, ISO 5208 defines seven leakage rates (A through G), allowing the specifier to choose the appropriate tightness level:
| Rate | Liquid Leakage (per mm DN per hour) | Gas Leakage (per mm DN per hour) | Application |
|---|
| A | Zero (no visible leakage) | Zero (no detectable leakage) | Soft-seated valves, critical isolation |
| AA | 0.01 mL | 0.3 mm3 (NTP) | Near-zero leakage |
| B | 0.03 mL | 0.9 mm3 (NTP) | High-performance metal seat |
| C | 0.1 mL | 3 mm3 (NTP) | Standard metal-seated gate valve |
| D | 0.3 mL | 9 mm3 (NTP) | General metal-seated service |
| E | 1.0 mL | 30 mm3 (NTP) | Non-critical service |
| F | 3.0 mL | 300 mm3 (NTP) | Low-criticality |
| G | 6.0 mL | 600 mm3 (NTP) | Minimum requirement |
Leakage rates scale with valve size (DN). A DN 200 valve at Rate D is allowed 200 x 0.3 = 60 mL/h of liquid leakage.
ISO 5208 vs API 598
| Feature | ISO 5208 | API 598 |
|---|
| Scope | International (ISO) | North American (API) |
| Shell test pressure | 1.5x maximum allowable pressure | 1.5x CWP |
| Closure test pressure | 1.1x maximum allowable pressure | 1.1x CWP |
| Leakage classification | 7 rates (A through G) | 2 rates (Rate A and Rate B) |
| Leakage specification | Per mm DN (normalized to size) | Per valve size (table values) |
| Test duration | Based on valve size | Based on valve size |
| Gas closure test | Standard requirement | Standard requirement |
| Primary market | Europe, international | North America, oil and gas |
ISO 5208 vs FCI 70-2
| Feature | ISO 5208 | FCI 70-2 |
|---|
| Scope | All industrial valves (factory test) | Control valves (seat leakage classification) |
| Rates/Classes | A through G | Class I through VI |
| Test conditions | Factory hydrostatic and pneumatic | Operating or test conditions |
| Application | Procurement acceptance testing | Control valve specification |
Test Duration by Valve Size
| DN | Test Duration (Minimum) |
|---|
| Up to DN 50 | 15 seconds |
| DN 65 to DN 150 | 60 seconds |
| DN 200 to DN 300 | 120 seconds |
| DN 350 to DN 600 | 300 seconds |
| Above DN 600 | By agreement |
Specifying the Correct Rate
The valve leakage rate must be specified on the purchase order. If not specified, the default rates in the applicable product standard apply:
Read the full guide to valve types
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