Stainless Steel Seamless Pipe Composition for CO2 and SSC Resistance
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Solution Overview
Problem
Conventional stainless steel seamless pipes for oil wells lack sufficient yield stress, low-temperature toughness, high-temperature CO2 corrosion resistance, low-temperature SSC resistance, and corrosion resistance in acid environments, particularly in severe corrosion environments containing CO2, H2S, and chloride ions.
Innovation Solution
A stainless steel seamless pipe with a specific chemical composition containing Cr, Mo, Sb, Co, and Ca, and limited Ni, along with a microstructure of 30-50% martensite, 50% or less ferrite, and 40% or less retained austenite, combined with a quenching-tempering production process, to achieve yield stress of 758 MPa or more and excellent corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If 13Cr martensitic stainless steel pipes are used for oil wells in high-temperature environments, then the pipes can withstand high temperature, but the corrosion resistance in severe corrosion environments containing CO2, Cl−, and H2S is insufficient
Solution Approach 1:
The patent changes the chemical composition parameters by increasing Cr to 16-18%, Mo to 2.7-5.0%, Cu to 0.3-4.0%, and adding Sb to 0.001-1.0%, while controlling Ni to 3.0-6.0%. This parameter optimization enhances the pipe's corrosion resistance in high-temperature CO2, H2S, and chloride environments while maintaining high-temperature strength.
Solution Approach 2:
The patent creates a composite microstructure consisting of martensite (45-80%), ferrite (10-40%), and retained austenite (5-20%) phases. This composite structure combines the high strength of martensite with the corrosion resistance of ferrite and retained austenite, achieving both high-temperature strength and severe corrosion environment resistance.
2Strength
If the steel pipe composition is optimized for high strength, then the yield stress increases, but the low-temperature toughness may deteriorate
Solution Approach 1:
The patent optimizes alloying elements to control the balance between strength and toughness. Specifically, Cr content is controlled at 16-18% to provide strength while maintaining toughness, Ni is limited to 3.0-6.0% to avoid excessive hardening that would reduce toughness, and Sb is added at 0.001-1.0% to enhance strength without compromising low-temperature ductility.
Solution Approach 2:
The dual-phase composite microstructure of martensite and ferrite with retained austenite provides both high yield stress and low-temperature toughness. The ferrite phase contributes to toughness and ductility at low temperatures, while the martensite phase provides high strength, achieving a balanced performance suitable for cold region oil wells.
3Ease of manufacture
If conventional stainless steel composition is used, then the manufacturing process is simple, but the corrosion resistance in severe corrosion environments is insufficient
Solution Approach 1:
The patent modifies the chemical composition parameters by increasing Cr to 16-18%, Mo to 2.7-5.0%, and adding Sb to 0.001-1.0%, while controlling other elements within specific ranges. These parameter changes enhance corrosion resistance in severe environments while maintaining compatibility with conventional stainless steel manufacturing processes.
Solution Approach 2:
The patent applies local quality enhancement by adding Sb (0.001-1.0%) specifically to improve corrosion resistance in severe environments, while maintaining the overall austenitic microstructure and conventional manufacturing approach. This localized compositional adjustment provides enhanced protection without fundamentally changing the manufacturing process.
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 pipe exhibits high strength, excellent low-temperature toughness, and corrosion resistance in high-temperature CO2 environments, low-temperature SSC resistance, and corrosion resistance in acid environments, meeting the demands of severe oil well conditions.
Implementation Method 1
heating the seamless steel pipe to a quenching temperature of 850°C to 1150°C; cooling the seamless steel pipe after the heating to a cooling stop temperature of 50°C or less at a cooling rate of 0.01°C/s or more
Implementation Method 2
heating the seamless steel pipe after the cooling to a tempering temperature of 500°C to 650°C, to produce a stainless steel seamless pipe having: 30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase
Data Source
AI summary
Provided is a stainless steel seamless pipe having high strength and excellent low-temperature toughness and corrosion resistance. The stainless steel seamless pipe comprises: a predetermined chemical composition; 30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase in volume fraction; a yield stress of 758 MPa or more; and a Charpy absorbed energy vE−10 at −10° C. of 40 J or more.