Seamless Stainless Steel Pipe Composition for Corrosive Oil Wells
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Solution Overview
Problem
Existing stainless steel seamless pipes used in oil country tubular goods lack sufficient high-temperature corrosion resistance, acid-environment corrosion resistance, and low-temperature toughness, making them unsuitable for severe environments in oil and gas wells.
Innovation Solution
A stainless steel seamless pipe composition containing specific amounts of Cr, Mo, Cu, Ni, and Sn, with a microstructure of 30-65% martensitic phase, 40% or less ferrite phase, and 30% or less retained austenite phase, and a manufacturing process involving hot working, quenching, and tempering to achieve a yield strength of 758 MPa or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 13Cr martensitic stainless steel pipes are used for oil country tubular goods, then the pipes can provide basic strength, but the corrosion resistance in high-temperature corrosive environments containing CO2 and Cl- is insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the stainless steel by adding specific amounts of Cr (18-23%), Mo (2.0-4.0%), Cu (0.5-3.0%), Ni (3.0-6.0%), and Sn (0.01-1.0%), while controlling C (0.05-0.25%), Si (0.01-1.0%), Mn (0.01-2.0%), P (0.01-0.05%), S (0.001-0.01%), Al (0.01-0.10%), N (0.01-0.10%), and O (0.003-0.030%). These parameter changes resolve the contradiction by providing both the required strength and improved corrosion resistance in high-temperature environments containing CO2 and Cl-.
Solution Approach 2:
The invention creates a composite microstructure consisting of martensitic phase (40-70%), ferrite phase (10-40%), and retained austenite phase (5-30%). This composite microstructure resolves the contradiction by combining the high strength of martensite with the corrosion resistance and toughness provided by ferrite and retained austenite, achieving both strength requirements and improved corrosion resistance in severe environments.
2Reliability
If the steel composition is optimized for high-temperature corrosion resistance, then corrosion rate decreases, but the low-temperature toughness may be compromised
Solution Approach 1:
The invention carefully balances composition parameters, particularly adding Sn (0.01-1.0%) for corrosion resistance while controlling C (0.05-0.25%) to prevent excessive brittleness. The addition of Ni (3.0-6.0%) and controlled amounts of alloying elements maintains low-temperature toughness while achieving high-temperature corrosion resistance through the formation of a stable passive film.
Solution Approach 2:
The tri-phase composite microstructure (martensitic phase 40-70%, ferrite phase 10-40%, retained austenite phase 5-30%) resolves this contradiction by combining phases with complementary properties: martensite provides strength, ferrite provides ductility and toughness, and retained austenite provides work hardening capability. This composite structure achieves both high-temperature corrosion resistance and desirable low-temperature toughness.
3Reliability
If the steel composition is optimized for acid-environment corrosion resistance, then corrosion rate in acid decreases, but the manufacturing complexity increases
Solution Approach 1:
The invention optimizes composition parameters for acid-environment corrosion resistance by adding Cr (18-23%) and Mo (2.0-4.0%) to form a stable passive film, and Cu (0.5-3.0%) to enhance resistance to sulfuric acid corrosion. While the composition control is precise, the invention provides clear numerical ranges for each element, making the manufacturing process manageable and reproducible.
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 excellent corrosion resistance in high-temperature and acid environments, with a corrosion rate of 0.127 mm/y or less and 600 mm/y or less, respectively, and desirable low-temperature toughness with an absorption energy of 200 J or more, meeting the demands of oil and gas well applications.
Implementation Method 1
hot working a steel pipe material into a seamless steel pipe
Implementation Method 2
quenching that reheats the seamless steel pipe to a temperature of 850 to 1,150° C., and cools the seamless steel pipe at a cooling rate of air cooling or faster
Implementation Method 3
tempering that heats the quenched seamless steel pipe to a temperature of 500 to 650° C.
Data Source
AI summary
A stainless steel seamless pipe has a composition that contains, in mass %, C: 0.06% or less, Si: 1.0% or less, Mn: 0.01% or more and 1.0% or less, P: 0.05% or less, S: 0.005% or less, Cr: 15.2% or more and 18.5% or less, Mo: 1.5% or more and 4.3% or less, Cu: 1.1% or more and 3.5% or less, Ni: 3.0% or more and 6.5% or less, Al: 0.10% or less, N: 0.10% or less, O: 0.010% or less, and Sn: 0.001% or more and 1.000% or less, and in which C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfy the predetermined formula, and the balance is Fe and incidental impurities, the stainless steel seamless pipe having a microstructure containing 30% or more martensitic phase, 65% or less ferrite phase, and 40% or less retained austenite phase by volume.