Introduction: Why API 598 Matters
In high-risk industries like oil, gas, and petrochemicals, valve reliability is non-negotiable. API 598 “Valve Inspection and Testing” is the global benchmark ensuring structural integrity and leak-tight performance. This standard provides unified procedures for inspectors to validate quality and empowers procurement teams to define technical requirements and mitigate supply chain risks.
What is API 598
Published by the American Petroleum Institute (API), API 598 specifies mandatory pre-shipment inspection and pressure testing protocols for metal valves used in hydrocarbon industries.
Key Objectives
• Verify structural strength (pressure containment)
• Validate sealing performance (internal/external leakage)
• Standardize acceptance criteria globally
Critical Importance
• For Inspectors: Provides enforceable test methodologies
• For Buyers: Forms the core of procurement specifications and contractual compliance
API 598 Testing Procedures: Step-by-Step Compliance
1. Scope & Referenced Standards
Defines applicable valve types (see Section 3) and linked standards (API 6D, ASME B16.34, etc.).
2. Inspection Requirements
• Responsibility: Manufacturer-led
• Key Checks:
→ Material certification
→ Dimensional accuracy
→ NDT (RT/UT/MT/PT as per product standards)
→ Visual defects
→ Marking/nameplate compliance
→ Coating integrity
3. Pressure Testing (Critical Section)
Test Types & Procedures
| Test Type | Purpose | Valve State | Medium | Pressure | Duration (min) |
|---|---|---|---|---|---|
| Shell Test | Body/bonnet integrity | Open | Water | 1.5x MAWP @ 38°C (100°F) | ≥NPS 2: 60s |
| Backseat Test | Stem/bonnet seal (if applicable) | Open | Water/Gas (Low) | 1.1x MAWP @ 38°C (100°F) | = Shell Test |
| High-Pressure Seat Test | Primary sealing performance | Closed | Water (Liquid valves) | 1.1x MAWP @ 38°C (100°F) | NPS 4+: 60s |
| Low-Pressure Seat Test | Gas sealing verification | Closed | Air/Nitrogen | 0.5–0.7 MPa (6–8 bar) | = High-Pressure |
| DBB Test | Dual isolation & bleed function | Closed | Water/Gas | Per Seat Test | Per Seat Test |
Leakage Acceptance Criteria
• Shell/Backseat Tests: Zero visible leakage
• High-Pressure Liquid Test (Metal Seat): No visible droplets
• Gas Test Bubble Rates (per minute):
| Valve Type | Size (NPS) | Max Bubbles/min |
|---|---|---|
| Gate/Globe/Ball | ≤2.5 | 0 |
| 3–6 | 12 | |
| ≥8 | 20 | |
| Butterfly (Metal) | ≤2.5 | 0 |
| 3–6 | 24 | |
| ≥8 | 40 | |
| All Soft Seats | Any | 0 |
4. Post-Test Handling
Mandatory drying (critical for stainless steel) and re-preservation.
5. Certification
Compliant valves receive API monogram (where applicable) and test reports.
Valves Covered by API 598
Applies to metal valves manufactured to:
√ API 6D: Pipeline Valves (Ball/Gate/Plug/Check)
√ API 6A: Wellhead Valves
√ API 600/602/603: Steel Gate Valves
√ API 608: Metal Ball Valves
√ API 609: Butterfly Valves
√ API 623: Steel Globe Valves
Key Note: API 598 is a testing standard. Valve design/material requirements are defined in product standards (e.g., API 6D). Contracts must reference BOTH.
Practical Guidance for Professionals
For Inspectors
1. Master latest API 598 edition + linked product standards
2. Calibrate test equipment (gauges, timers) quarterly
3. Document bubble counts/photograph leaks
4. Enforce safety during gas tests
For Procurement Teams
1. Specify in contracts:Require witnessed Factory Acceptance Tests (FAT)
• ”Valves shall be tested per API 598, 11th Ed (current)”
• Referenced product standard (e.g., API 6D 25th Ed)
2. Demand original signed test reports
3. Include supplementary requirements:
• Fire testing (API 607/6FA)
• Fugitive emissions (ISO 15848)
Conclusion: The Quality Imperative
API 598 isn’t just a standard—it’s your frontline defense against valve failures. For inspectors, it’s the definitive playbook. For procurement, it’s risk mitigation embodied. As processing environments grow more extreme, rigorous API 598 compliance remains non-negotiable for safety, sustainability, and operational excellence.
Post time: Jul-22-2025