SHANGHAI RUICHAO INDUSTRIAL
SHANGHAI RUICHAO INDUSTRIAL
Line pipe steel is a category of high-strength, low-alloy (HSLA) steel specifically engineered for the construction of pipelines that transport oil, gas, and other fluids over long distances. It is characterized by its high yield strength, excellent toughness at low temperatures to prevent brittle fracture, superior weldability for secure field joints, and enhanced resistance to internal pressure and external stresses like soil movement and seismic activity. This steel is primarily used in the manufacturing of seamless or welded pipes for onshore and offshore transmission pipelines, gathering lines, and distribution networks, where reliability, durability, and resistance to environmental cracking are critical for safe and efficient operation.
Specification Parameters
| Parameters of Line Pipe Steel | |||
| Parameter Category | Specific Parameter | Typical Value / Description | Importance for Pipeline Applications |
| Mechanical Properties | Yield Strength (YS) | Grade X42 to X120 (e.g., 290 MPa to 830 MPa Min. YS) | Must reliably resist internal hoop stress from high pressure. Higher grades allow thinner walls or higher pressures. |
| Tensile Strength (TS) | 415 MPa to 1035 MPa+ | Must be high and have a specific ratio to YS (typically TS/YS < 0.93) to prevent plastic collapse and ensure strain-based design capability. | |
| Charpy V-Notch Impact Toughness | Very High (e.g., > 200 J @ -10°C to -40°C) | Critical. Prevents running brittle fracture in the event of a failure. Test temperature is set below the pipeline's minimum operating temperature. | |
| Drop-Weight Tear Test (DWTT) | > 85% Shear Area (typically @ -5°C to -30°C) | Measures resistance to propagating a ductile fracture. A mandatory parameter to ensure fracture arrest. | |
| Hardness (HV10) | Often limited to max. 248 or 275 HV10 | Controlled to minimize risk of Hydrogen-Induced Cracking (HIC) and Sulfide Stress Cracking (SSC) in sour service. | |
| Chemical Composition | Carbon (C) Equivalent (CE/Pcm) | Strictly controlled (e.g., CEIIW < 0.43, Pcm < 0.23) | Calculated formulas ensure excellent weldability for field girth welding, even under challenging conditions. |
| Microalloying Elements | Niobium (Nb), Vanadium (V), Titanium (Ti) | Primary method for achieving high strength through grain refinement and precipitation hardening. | |
| Sulfur (S) & Phosphorus (P) | Kept extremely low (e.g., S < 0.002%, P < 0.015%) | "Clean steel" practice is essential to maximize toughness and minimize HIC/SSC susceptibility. | |
| Calcium (Ca) Treatment | Often used | Helps control sulfide shape (forms globular CaS instead of elongated MnS), further improving HIC resistance. | |
| Dimensional & Testing | Diameter & Wall Thickness (WT) | Wide range (e.g., 18" to 56" diameter, WT up to 40mm+) | Designed for specific pressure, depth (for offshore), and external load requirements. |
| Hydrostatic Test Pressure | ≥ 90% of Specified Min. Yield Strength (SMYS) | Mandatory test on every length of pipe to verify integrity and strength. | |
| HIC/SSC Testing | NACE TM0284 / TM0177 Method A | For "sour service" pipes exposed to wet H₂S environments. Verifies resistance to hydrogen-related cracking. | |
