ASTM A234 WP9 Pipe Fittings – Complete Technical Specifications
1. Material Overview
ASTM A234 WP9 specifies 9Cr-1Mo-V alloy steel pipe fittings for ultra-high temperature service (up to 1200°F/650°C). These fittings offer:
– Superior creep strength
– Exceptional oxidation resistance
– Enhanced thermal fatigue resistance
– Good corrosion resistance in sulfur-containing environments
2. Chemical Composition (%)
| Element | Composition Range | Key Effect |
|———|——————-|————|
| Carbon (C) | 0.15 max | Controls hardness |
| Manganese (Mn) | 0.30-0.60 | Strength & hardenability |
| Phosphorus (P) | 0.025 max | Impurity control |
| Sulfur (S) | 0.025 max | Impurity control |
| Silicon (Si) | 0.25-1.00 | Deoxidizer |
| Chromium (Cr) | 8.00-10.00 | Oxidation resistance |
| Molybdenum (Mo) | 0.90-1.10 | Creep strength |
| Vanadium (V) | 0.18-0.25 | Carbide stabilization |
3. Mechanical Properties
| Property | Requirements | Test Method |
|———-|————–|————-|
| Tensile Strength | 585-760 MPa (85,000-110,000 psi) | ASTM A370 |
| Yield Strength | 415 MPa min (60,000 psi min) | ASTM A370 |
| Elongation | 20% min | ASTM A370 |
| Hardness | ≤248 HB / ≤25 HRC | ASTM E10/E18 |
| Impact Energy | 20J min (15 ft-lb) @ room temp | ASTM A370 |
4. Temperature Capabilities
– **Maximum Continuous Service**: 650°C (1200°F)
– **Short-term Exposure Limit**: 700°C (1290°F)
– **Minimum Temperature**: -29°C (-20°F) with impact testing
– **Optimum Range**: 540-650°C (1000-1200°F)
5. Manufacturing Standards
– **Base Specification**: ASTM A234
– **Dimensional Standards**:
– ASME B16.9 (Factory-made butt-welding fittings)
– ASME B16.28 (Short radius elbows)
– **Heat Treatment**:
– Normalizing: 1040-1080°C (1900-1975°F)
– Tempering: 730-790°C (1350-1450°F)
6. Available Fitting Types
1. **Elbows** (45°/90°/180°; Short/Long Radius)
2. **Tees** (Straight & Reducing)
3. **Reducers** (Concentric & Eccentric)
4. **Caps**
5. **Stub Ends**
6. **Crosses**
7. **Lap Joint Stub Ends**
7. Heat Treatment Requirements
– **Post-Fabrication Heat Treatment**:
– Normalizing: Mandatory
– Tempering: Mandatory
– **PWHT Requirements**:
– Temperature: 730-760°C (1350-1400°F)
– Holding Time: 1 hour/inch thickness (minimum 1 hour)
– Cooling Rate: ≤55°C/h (100°F/h) to 315°C (600°F)
8. Welding Considerations
– **Preheat Temperature**: 200-300°C (400-600°F)
– **Interpass Temperature**: ≤300°C (≤600°F)
– **Recommended Filler Metals**:
– SMAW: E505-XX (AWS A5.5)
– GTAW/GMAW: ER505 (AWS A5.28)
– **Post-Weld Heat Treatment**: Mandatory
9. Quality Control
– **Mandatory Tests**:
– Hydrostatic testing (1.5x design pressure)
– Tensile testing
– Hardness survey
– **Optional Tests**:
– Charpy V-notch impact testing
– Positive Material Identification (PMI)
– Full radiographic examination
– Ferrite content verification
10. Corrosion Resistance
– **Oxidation Resistance**: Excellent up to 650°C
– **Sulfidation Resistance**: Superior to lower alloy steels
– **Steam Oxidation**: Excellent resistance
– **Hydrogen Attack**: Good resistance at moderate temps
11. Applications
– **Power Generation**:
– Superheater outlets
– Main steam lines
– Hot reheat piping
– **Petrochemical**:
– Hydroprocessing units
– Catalytic reformers
– High-temperature reactors
– **Refineries**:
– Coker units
– FCC units
– High-pressure manifolds
12. Comparison with Similar Grades
| Grade | Cr% | Mo% | V% | Key Difference |
|——-|—–|—–|—-|—————-|
| WP5 | 4-6 | 0.5 | – | Lower Cr content |
| WP22 | 2.25 | 1.0 | – | Different Cr-Mo ratio |
| WP91 | 8-9.5 | 0.85-1.05 | 0.18-0.25 | Similar but with Nb & N |
13. Purchasing Specifications
Essential ordering details:
1. Full material designation (ASTM A234 WP9)
2. Fitting type and exact dimensions
3. Wall thickness/Schedule
4. Heat treatment condition
5. End preparation details
6. Required certifications (EN 10204 3.1/3.2)
7. Special testing requirements
8. Surface finish specifications
14. Maintenance Requirements
– **Inspection Frequency**:
– Critical service: Quarterly
– Standard service: Biannually
– **Key Inspection Methods**:
– Ultrasonic thickness monitoring
– Dye penetrant inspection
– Replica metallography for creep assessment
– Hardness mapping of HAZ regions
– **Replacement Criteria**:
– 15% wall thinning
– Visible creep damage
– Microcracking in HAZ
– Excessive hardness variations
15. Special Considerations
1. **Thermal Cycling**: WP9 exhibits excellent resistance to thermal fatigue
2. **Aging Effects**: Long-term exposure at high temps requires microstructural evaluation
3. **Welding Precautions**: Strict control of heat input and interpass temp required
4. **Storage**: Protect from moisture to prevent pitting corrosion
5. **Installation**: Proper alignment to minimize stress concentrations
WP9 fittings require specialized welding procedures and heat treatment. Always consult ASME B31.1 (Power Piping) or B31.3 (Process Piping) for specific application requirements. For temperatures above 593°C (1100°F), consider WP91 for enhanced creep strength.
