Stainless Steel Pipe Composition for CO2 Corrosion Resistance
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Solution Overview
Problem
Steel pipes for oil country tubular goods face challenges in maintaining high strength and corrosion resistance in severe corrosive environments with high CO2 and Cl- concentrations at temperatures of 150°C or higher, while also experiencing issues with hot workability and strength scattering.
Innovation Solution
A stainless steel seamless pipe composition is developed with specific ranges of elements such as Cr, Ni, Mo, Cu, and C, along with additional elements like Co, to achieve a yield strength of 655 MPa or more, improved carbon dioxide corrosion resistance, and enhanced hot workability, by satisfying specific relational expressions and phase fractions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If 13Cr martensitic stainless steel is used to achieve high strength, then strength is improved, but corrosion resistance in severe CO2 and Cl- environments deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the stainless steel by adding specific elements (Co: 0.01-1.0%, Ti: 0.01-0.06%, B: 0.0005-0.005%) and adjusting the ranges of existing elements (Cr: 12-17%, Ni: 4-7%, Mo: 0.5-3%) to simultaneously achieve high strength and excellent corrosion resistance in severe CO2 and Cl- environments at high temperatures
Solution Approach 2:
The invention creates a composite microstructure consisting of martensite phase (40-90% by area), retained austenite phase (5-60% by area), and carbide precipitates, where each phase contributes different properties: martensite provides strength, retained austenite provides ductility and corrosion resistance, and carbides provide precipitation hardening, achieving synergistic effect for both high strength and corrosion resistance
2Reliability
If high chromium and nickel content is increased to improve corrosion resistance, then corrosion resistance is improved, but hot workability deteriorates
Solution Approach 1:
The invention optimizes the balance between Cr (12-17%) and Ni (4-7%) content while adding small amounts of Co (0.01-1.0%), Ti (0.01-0.06%), and B (0.0005-0.005%) to achieve the desired corrosion resistance without excessive Cr and Ni content that would harm hot workability, and controls the relational expression Cr+Ni≤28 to maintain hot workability
3Strength
If carbon content is increased to improve strength, then strength is improved, but corrosion resistance and hot workability deteriorate
Solution Approach 1:
The invention maintains low carbon content (C: 0.005-0.03%) to preserve corrosion resistance and hot workability, and compensates for strength through adding Co (0.01-1.0%) for solid solution strengthening, Ti (0.01-0.06%) for carbide precipitation strengthening, and controlling the martensite phase composition and structure
4Reliability
If alloying elements are increased to improve corrosion resistance, then corrosion resistance is improved, but manufacturing cost increases
Solution Approach 1:
The invention uses moderate amounts of expensive alloying elements (Co: 0.01-1.0%, Ti: 0.01-0.06%, B: 0.0005-0.005%) combined with optimized ranges of more affordable elements (Cr: 12-17%, Ni: 4-7%, Mo: 0.5-3%) to achieve the required corrosion resistance at a balanced cost, avoiding excessive use of expensive rare earth elements while maintaining performance through precise compositional control and phase structure optimization
Data Source
AI summary
A high strength stainless steel seamless pipe for oil country tubular goods which is excellent in hot workability, has a high strength, suppresses scattering in the strength, and has excellent carbon dioxide corrosion resistance. The steel pipe has a yield strength of 655 MPa or more, and a chemical composition comprising, by mass %, C: 0.005 to 0.05%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 12.0 to 17.0%, Ni: 4.0 to 7.0%, Mo: 0.5 to 3.0%, Al: 0.005 to 0.10%, V: 0.005 to 0.20%, Co: 0.01 to 1.0%, N: 0.005 to 0.15%, and O: 0.010% or less with the balance being Fe and inevitable impurities. Cr, Ni, Mo, Cu, and C satisfy a specified expression, and Cr, Mo, Si, C, Mn, Ni, Cu, and N satisfy another specified expression.