What Is API 574?
Quick Answer: API 574 (Inspection Practices for Piping System Components) is a recommended practice that supplements API 570 by providing detailed guidance on how to inspect specific piping components. While API 570 sets mandatory inspection requirements and intervals, API 574 describes the practical inspection techniques for valves, fittings, flanges, bolting, gaskets, and piping supports.
API 574 vs. API 570
| Aspect | API 570 | API 574 |
|---|---|---|
| Document type | Inspection Code (mandatory requirements) | Recommended Practice (guidance) |
| Focus | When and how often to inspect; remaining life; repair/alteration rules | How to inspect specific components; what to look for |
| Scope | Entire piping circuit risk classification and interval | Individual component inspection techniques |
| Certification | API 570 Inspector certification exam | Covered within the API 570 exam body of knowledge |
| Compliance | Required by many jurisdictions and owner/operators | Supplementary guidance; not independently mandatory |
What API 574 Covers
API 574 provides inspection guidance for every component type in a piping system:
| Component | Key Inspection Points per API 574 |
|---|---|
| Straight pipe | Wall thinning (general and localized), external corrosion, CUI, erosion at bends |
| Butt weld fittings | Weld integrity, thinning at elbows (extrados), tee branch reinforcement |
| Flanges | Flange face damage, bolt hole elongation, gasket seating surface, bolt corrosion |
| Valves | Body wall thinning, packing leaks, bonnet bolting, seat erosion |
| Gaskets | Leakage, compression state, material degradation |
| Stud bolts | Corrosion, stress relaxation (creep), thread damage |
| Supports and hangers | Overloading, corrosion, missing components, thermal movement |
| Small-bore connections | Vibration fatigue, socket weld cracking, threaded joint leaks |
| Expansion joints | Bellows cracking, tie rod condition, movement indicators |
Common Corrosion Mechanisms
API 574 describes corrosion and degradation mechanisms that inspectors should recognize:
| Mechanism | Where Found | Detection Method |
|---|---|---|
| General corrosion | All carbon steel piping in corrosive service | UT thickness measurement |
| Corrosion under insulation (CUI) | Insulated carbon steel piping, 50-175 degC | Insulation removal, profile RT, pulsed eddy current |
| Erosion | Downstream of control valves, elbows, tees in high-velocity service | UT at wear points, guided wave UT |
| Microbiologically influenced corrosion (MIC) | Water systems, deadlegs, stagnant areas | Internal visual, pit depth measurement |
| Stress corrosion cracking (SCC) | Stainless steel in chloride service, carbon steel in amine/caustic | Wet fluorescent magnetic particle (WFMT), phased array UT |
| Creep | Cr-Mo piping above 450 degC | Replication, hardness testing, dimensional measurement |
| Hydrogen damage | Carbon steel in high-temperature hydrogen service | Advanced UT (TOFD, phased array) |
Inspection Techniques Referenced
API 574 references non-destructive testing methods including:
- Ultrasonic thickness measurement (most common)
- Radiographic testing (profile and tangential)
- Guided wave ultrasonic testing (GWUT) for long pipe runs
- Phased array ultrasonic testing (PAUT) for weld inspection
- Visual examination (direct and remote/drone)
API 574 is required study material for the API 570 certification exam and a practical field reference for piping inspectors.
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