Seamless Steel Pipe Heat Treatment for Sour Service Strength
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Solution Overview
Problem
Existing steel pipes for oil and gas wells in sour environments lack sufficient sulfide stress corrosion cracking resistance, as measured by the K ILIMIT value, which is not adequately addressed by previous technologies.
Innovation Solution
A high-strength seamless steel pipe composition and manufacturing process that includes intermediate cooling and reheating steps to achieve a K ILIMIT value of 23.0 MPa√m or more, involving specific temperature and time controls during hot rolling and quenching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional steel pipe materials and processes are used, then manufacturing simplicity is maintained, but sulfide stress corrosion cracking resistance (K_ILIMIT value) is insufficient
Solution Approach 1:
The hot rolling process is divided into multiple stages with intermediate cooling and reheating steps. The cooling process is segmented into controlled rates (40-100°C/s) to achieve specific microstructural transformations, thereby improving SSC resistance without excessive complexity
Solution Approach 2:
Specific compositional parameters (C: 0.20-0.35%, Si: 0.05-0.50%, Mn: 0.05-1.00%, Cr: 0.10-1.00%, Mo: 0.50-1.00%, B: 0.0001-0.0050%) and process parameters (cooling rates, temperatures) are optimized to achieve the required K_ILIMIT value of 23.0 MPa√m or more
2Strength
If high strength equivalent to API C110 grade is achieved, then mechanical strength is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise compositional ranges and process parameters (heating temperatures, cooling rates, holding times) to achieve yield strength of 758 MPa or more while maintaining manufacturability through defined parameter windows
Solution Approach 2:
The manufacturing process incorporates controlled cooling rates (40-100°C/s) and specific temperature thresholds (Ar3 transformation point) that act as feedback mechanisms to ensure consistent microstructural development and strength properties
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 process results in a steel pipe with high strength equivalent to API C110 grade and excellent sulfide stress corrosion cracking resistance, ensuring stability in hydrogen sulfide-containing environments.
Implementation Method 1
a first hot rolling step of hot rolling the heated steel pipe material by piercing and elongating the steel pipe material; an intermediate cooling step of cooling a raw steel pipe after the first hot rolling step; an intermediate heating step of heating the raw steel pipe after the intermediate cooling step; a second hot rolling step of subjecting the raw steel pipe after the intermediate heating step to sizing hot rolling
Implementation Method 2
a direct quenching step of directly quenching the raw steel pipe continuously from the second hot rolling step; a heat treatment step of subjecting the raw steel pipe after the direct quenching step to at least one run of a heat treatment that quenches the raw steel pipe after reheating to a temperature of 850 to 930°C, and subsequently tempers the raw steel pipe by heating to 650 to 730°C
Data Source
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AI summary
Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a yield strength of 758 MPa or more, and a KILIMIT value of 23.0 MPa√m or more as an evaluation index of sulfide stress corrosion cracking resistance.