High-Strength Stainless Seamless Pipe for CO2 and SSC Resistance
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Solution Overview
Problem
Existing steel pipes for oil country tubular goods lack sufficient high strength, hot workability, and sulfide stress cracking resistance in severe corrosive environments, particularly in high-temperature conditions with carbon dioxide and chlorine ions, and low-temperature environments with hydrogen sulfide.
Innovation Solution
A high-strength stainless steel seamless pipe with a specific composition and microstructure, including controlled austenite grain size and balanced alloy elements, combined with a manufacturing process involving heating, hot working, quenching, and tempering, to achieve yield strength of 758 MPa or more, superior hot workability, and excellent corrosion and SSC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional stainless steel compositions are used for oil country tubular goods, then corrosion resistance is maintained, but strength is insufficient for deep well applications
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.005-0.05%, Si: 0.05-0.50%, Mn: 0.20-1.80%, Cr: 12.0-17.0%, Ni: 4.0-7.0%, Mo: 0.5-3.0%, Al: 0.005-0.10%, V: 0.005-0.20%, Co: 0.01-1.0%, N: 0.005-0.15%, O: 0.010% or less) and applying specific heat treatment parameters (heating to Ac3 transformation point or higher, quenching, and tempering at 500-650°C) to achieve both high strength (yield strength 655 MPa or more) and corrosion resistance simultaneously
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered martensite as the primary phase with controlled precipitates (carbides, carbonitrides, and intermetallic compounds from V, Nb, Ti, and Al) dispersed throughout, combining the high strength characteristics of martensite with the corrosion resistance provided by the specific alloy composition and microstructure
2Reliability
If high chromium and nickel contents are increased to improve corrosion resistance, then corrosion resistance improves, but manufacturing cost increases
Solution Approach 1:
The patent optimizes the parameters of alloying element contents to achieve effective corrosion resistance with reduced quantities: Cr is controlled at 12.0-17.0% (lower than conventional 18%), Ni at 4.0-7.0% (reduced from typical 8-10%), while adding smaller amounts of more efficient elements like Mo (0.5-3.0%), V (0.005-0.20%), and Co (0.01-1.0%) to enhance both corrosion resistance and strength, thereby reducing overall material cost
3Strength
If carbon content is increased to enhance strength, then yield strength improves, but sulfide stress cracking resistance deteriorates
Solution Approach 1:
The patent carefully controls the carbon content parameter at 0.005-0.05% to achieve sufficient strength while maintaining SSC resistance, and compensates for the strength contribution through optimized combinations of other alloying elements (Ni, Cr, Mo, V, Co) and through the tempered martensite microstructure with controlled precipitates, thereby decoupling the trade-off between strength and SSC resistance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a stainless steel seamless pipe with enhanced strength, hot workability, and improved resistance to carbon dioxide gas corrosion and sulfide stress cracking in extreme environments, ensuring reliability for deep oil and gas wells.
Implementation Method 1
heating a steel pipe material of said composition
Implementation Method 2
quenching, and tempering
Implementation Method 3
quenching, and tempering
Data Source
AI summary
A high-strength stainless steel seamless pipe for oil country tubular goods has a composition that comprises, in mass %, C: 0.002 to 0.05%, Si: 0.05 to 0.50%, Mn: 0.04 to 1.80%, P: 0.030% or less, S: 0.002% or less, Cr: more than 14.0% and 17.0% or less, Ni: 4.0 to 8.0%, Mo: 1.5 to 3.0%, Al: 0.005 to 0.10%, V: 0.005 to 0.20%, Co: 0.01 to 1.0%, N: 0.002 to 0.15%, and O: 0.006% or less, and that satisfies the predetermined formulae, and in which the balance is Fe and incidental impurities, the high-strength stainless steel seamless pipe having a microstructure containing prior austenite having an average grain size of 40 μm or less, the high-strength stainless steel seamless pipe having a yield strength of 758 MPa or more.