ASTM A691 1.25Cr steel pipe falls under the category of low-alloy chromium-molybdenum steel. Its chemical composition includes molybdenum in addition to approximately 1.25% chromium. This alloy formulation enhances the pipe's strength and oxidation resistance in high-temperature environments. The addition of chromium significantly improves corrosion resistance, particularly against oxidation and sulfidation corrosion at elevated temperatures, while molybdenum further strengthens high-temperature performance and creep resistance. Precise control of carbon, manganese, silicon, and other elements optimizes the material's overall properties.
What is A691 1.25 cr equivalent
ASTM A691 1-1/4CR equivalent to ASTM A335 P11 pipe, sometimes also named as ASTM A691 Grade 11 pipe.
A691 1.25Cr vs. A335 P11
| Feature | A691 1.25Cr (GR.1-1/4Cr CL22) | A335 P11 |
|---|---|---|
| Standard | High-pressure welded steel pipe standard (ERW/SAW welded pipe) | High-temperature seamless steel pipe standard |
| Manufacturing | Straight-seam welding (HF welding/submerged arc welding) | Hot-rolled/cold-drawn seamless forming |
| Chemical Composition | Cr: 1.00-1.50% Mo: 0.44-0.65% |
Cr: 1.00-1.50% Mo: 0.44-0.65% (Note: Similar composition) |
| Mechanical Properties | Tensile strength ≥585 MPa Yield strength ≥415 MPa |
Tensile strength ≥415 MPa Yield strength ≥205 MPa |
| Max Temperature | ≤540°C (after post-weld heat treatment) | ≤593°C (superior high-temperature resistance for seamless pipe) |
| Typical Applications | Oil/gas pipelines, medium-temperature pressure vessels | Power plant boiler tubes, high-temperature steam lines |
| Heat Treatment | Mandatory post-weld stress relief (PWHT) | Normalizing + tempering (no welding stress in seamless pipe) |
| H₂S Corrosion Resistance | Excellent (with compatible welding materials) | Good (no weld-related weakness) |
ASTM A691 Pipe Tensile Chart
| Grade | Tensile (MPa) | Yield (MPa) | Elong. (50mm) | Reduc'n of Area* |
|---|---|---|---|---|
| 1CR | 380 – 550 | 230 min | 22% min | – |
| 1-1/4CR | 415 – 585 | 240 min | 22% min | – |
| 2-1/4CR, 5CR, 9CR | 415 – 585 | 205 min | 18% min | 40% min |
| 91 | 415 – 585 | 205 min | 18% min | 40% min |
Chemical Analysis of ASTM A691 Material
| 1CR | 1-1/4CR | 2-1/4 CR | 5 CR | 9 CR | 91 | |
| C | 0.05-0.17 | 0.05-0.17 | 0.05-0.15 | 0.15 | 0.15 | 0.08-0.12 |
| Mn | 0.40-0.65 | 0.40-0.65 | 0.30-0.60 | 0.30-0.60 | 0.30-0.60 | 0.30-0.60 |
| P | 0.025 | 0.025 | 0.025 | 0.025 | 0.025 | 0.020 |
| S | 0.025 | 0.025 | 0.025 | 0.025 | 0.025 | 0.010 |
| Si | 0.15-0.40 | 0.50-0.80 | 0.50 | 0.50 | 1.00 | 0.20-0.50 |
| Cr | 0.80-1.15 | 1.00-1.50 | 2.00-2.50 | 4.00-6.00 | 8.00-10.00 | 8.00-9.50 |
| Mo | 0.45-0.60 | 0.45-0.65 | 0.90-1.10 | 0.45-0.65 | 0.90-1.10 | 0.85-1.05 |
| V | – | – | – | – | 0.04 | 0.18-0.25 |
ASME SA691 EFW Pipe Test and inspection
To ensure the quality of welded pipes, stringent non-destructive testing (NDT) must be conducted during the production process, including:
Ultrasonic Testing (UT): To detect internal defects in welds and base material.
Radiographic Testing (RT): To inspect weld quality.
Eddy Current Testing (ET): To identify surface and near-surface defects.
Hydrostatic Testing: To verify the pressure-bearing capacity of the pipes.
ASME SA691 EFW Pipe factory
