Seamless Stainless Steel Pipe Composition for CO2 and SSC Corrosion
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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, Sn, Co, and Ca, and limited Ni, along with a microstructure of 30% martensite, 50% ferrite, and 40% retained austenite phases, combined with a quenching-tempering production process, to achieve high yield stress and excellent corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stainless steel compositions are used, then manufacturing is simpler, but corrosion resistance in high-temperature CO2 and low-temperature SSC environments is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters within specific ranges: Cr (16-18%), Mo (1.8-3%), Cu (1.0-3.5%), Ni (3.0-5.5%), and adding small amounts of Sn (0.01-1.0%) and Co (0.01-1.0%). These parameter adjustments optimize the microstructure to achieve 30% martensite, 10-45% ferrite, and 30% or less retained austenite, thereby improving corrosion resistance in high-temperature CO2 and low-temperature SSC environments while maintaining manufacturing feasibility
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (martensite, ferrite, and retained austenite) with specific volume fractions. This composite microstructure combines the high strength of martensite with the corrosion resistance and ductility contributions from ferrite and retained austenite, achieving superior overall performance in severe corrosion environments
2Reliability
If higher Cr and Mo content is increased to improve corrosion resistance, then corrosion resistance improves, but manufacturing cost increases
Solution Approach 1:
The patent optimizes the parameters of alloying elements to achieve the desired corrosion resistance at reasonable cost. Specifically, Cr is controlled at 16-18% and Mo at 1.8-3%, which provides sufficient corrosion resistance without excessive material cost. The addition of smaller amounts of Cu (1.0-3.5%), Ni (3.0-5.5%), Sn (0.01-1.0%), and Co (0.01-1.0%) further enhances corrosion resistance in severe environments while keeping overall material cost manageable
3Strength
If yield stress is increased to 758 MPa or more, then strength improves, but low-temperature toughness may deteriorate
Solution Approach 1:
The patent carefully controls the chemical composition parameters to achieve the desired balance between strength and low-temperature toughness. The composition (C: 0.05% or less, Si: 1.0% or less, Mn: 0.01% to 1.0%, Cr: 16% to 18%, Mo: 1.8% to 3%, Cu: 1.0% to 3.5%, Ni: 3.0% to 5.5%, Sn: 0.01% to 1.0%, Co: 0.01% to 1.0%) is designed to form a microstructure with 30% martensite for strength, 10-45% ferrite for toughness, and 30% or less retained austenite for ductility, achieving yield stress of 758 MPa or more while maintaining Charpy absorbed energy of 40 J or more at -10°C
Solution Approach 2:
The patent creates a composite microstructure with multiple phases in specific proportions: martensite (30% or more) provides high strength and yield stress, ferrite (10% to 45%) contributes to low-temperature toughness and ductility, and retained austenite (30% or less) enhances overall toughness and energy absorption. This composite microstructure achieves the difficult balance of yield stress ≥758 MPa while maintaining excellent low-temperature toughness with Charpy energy ≥40J at -10°C
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 achieves a yield stress of 758 MPa or more, excellent low-temperature toughness, and corrosion resistance in high-temperature CO2, low-temperature SSC, and acid environments, with corrosion rates and Charpy absorbed energy meeting specified criteria.
Implementation Method 1
a microstructure containing, in volume fraction, 30% or more martensite phase, 50% or less ferrite phase, and 40% or less retained austenite phase
Implementation Method 2
quenching-tempering production process
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.