SA691 Grade 5CR Chrome-Molybdenum Alloy Steel Boiler Pipe
Product Overview
SA691 Grade 5CR is a medium chromium-molybdenum alloy steel, electric fusion welded (EFW) pipe conforming to the ASTM/ASME SA691 standard. This grade is renowned for its excellent high-temperature strength, creep resistance, and resistance to hydrogen attack. Its alloy composition (approximately 5% chromium and 0.5% molybdenum) provides significantly superior performance compared to lower chromium grades like 1CR or 2CR, making it suitable for more severe high-temperature and high-pressure service.
Primary Applications
Power Plant Boilers: High-temperature and high-pressure steam lines, superheater, and reheater tubing.
Petrochemical & Refining: Piping for reactor effluent/feed exchangers, heater tubes, and transfer lines in hydroprocessing units (resistant to high-temperature hydrogen attack).
Refinery Heaters: Heater and reformer furnace tubes.
General High-Pressure High-Temperature Piping Systems.
SA691 5CR Chemical Composition & Mechanical Properties Table
| Category | Property / Element | Specification / Value |
|---|---|---|
| Standard & Grade | Standard Designation | ASTM/ASME SA691 |
| Grade | 5CR (Compositionally equivalent to ASTM A335 P5/P5c) | |
| Chemical Composition | Carbon (C) | 0.15% max |
| Manganese (Mn) | 0.30 - 0.60% | |
| Phosphorus (P) | 0.025% max | |
| Sulfur (S) | 0.025% max | |
| Silicon (Si) | 0.50% max | |
| Chromium (Cr) | 4.00 - 6.00% | |
| Molybdenum (Mo) | 0.45 - 0.65% | |
| Mechanical Properties | Tensile Strength, min | 415 MPa (60,000 psi) |
| Yield Strength, min | 205 MPa (30,000 psi) | |
| Elongation, min | Varies with wall thickness; typically ≥30% in 2 inches (50mm) | |
| Heat Treatment | Condition | Mandatory full annealing or normalizing and tempering to ensure a stable microstructure and mechanical properties. |
| Manufacturing Process | Type | Primarily Electric Fusion Welded (EFW), followed by full heat treatment. |
Key Characteristics & Additional Information
Elevated Temperature Service: The 5% chromium content significantly enhances the steel's oxidation resistance and creep rupture strength, allowing for long-term service in temperatures exceeding 593°C (1100°F).
Resistance to Hydrogen Attack: The addition of chromium forms stable carbides, providing effective resistance against hydrogen embrittlement and high-temperature hydrogen attack (HTHA), which is the primary reason for its widespread use in petrochemical hydroprocessing units.
Criticality of Heat Treatment: SA691 5CR welded pipe must be properly heat treated. This is essential not only to meet mechanical properties but also to:
Improve the properties of the weld heat-affected zone (HAZ).
Relieve residual stresses from welding.
Achieve a stable tempered microstructure.
Correlation with Seamless Pipe: SA691 5CR is essentially the welded pipe equivalent of the seamless pipe grade ASTM A335 Gr. P5. It serves as a cost-effective alternative where the design codes and service conditions permit the use of welded construction.
Procurement & Inspection:
Dimensions: Outside diameter and wall thickness per ASME B36.10M or purchase order requirements.
Testing & Inspection: Typically includes hydrostatic or non-destructive electric testing, chemical analysis, tension tests, hardness tests, and microstructural examination.
Documentation: A certified Material Test Report (MTR) / Mill Test Certificate (MTC) from the manufacturer, reporting all required test results, is mandatory.
Important Note: The information provided is based on general specifications. For any specific project, engineers must consult the latest official ASTM/ASME SA691 specification, project-specific technical requirements, and applicable design codes (e.g., ASME B31.1 or B31.3) for final material selection, design, and procurement.
