Seamless Steel Pipe for Deep-Sea Riser Toughness
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Solution Overview
Problem
Existing seamless steel pipes for deep-sea applications, such as flow lines and risers, face challenges in achieving high strength, toughness, and corrosion resistance, particularly for thick-walled pipes, as conventional methods are inadequate in ensuring these properties when used in severe deep-sea conditions.
Innovation Solution
A seamless steel pipe with a specific chemical composition containing C: 0.02-0.08%, Si: at most 0.5%, Mn: 1.5-3.0%, Mo: greater than 0.4%-1.2%, and additional elements like Ca or REM, with a product of Mn and Mo content between 0.8 and 2.6, combined with a manufacturing process involving hot working, quenching, and tempering, to enhance hardenability and tempering resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional seamless steel pipe manufacturing methods are used, then the production process is relatively simple, but the steel pipe cannot achieve high strength, toughness, and corrosion resistance required for deep-sea applications
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.02-0.08%, Si: 0.03-0.50%, Mn: 1.50-3.00%, Mo: 0.40-1.20%, and their products) and heat treatment parameters (quenching temperature, tempering temperature, cooling rate) to achieve high strength properties in the steel pipe while managing manufacturing complexity
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (martensite, bainite, and retained austenite) through controlled composition and heat treatment, achieving superior mechanical properties that cannot be obtained with single-phase structures
2Stress or pressure
If the wall thickness is increased to withstand deep-sea pressure, then the pipe can withstand higher external pressure, but the toughness and hardenability become more difficult to ensure
Solution Approach 1:
The patent changes the chemical composition parameters by adding Mo (0.40-1.20%) which significantly improves hardenability, and controlling the product of Mn×Mo (0.80-2.60) to ensure that even in thick-walled pipes, the microstructure can be properly transformed during heat treatment to achieve required toughness
Solution Approach 2:
The patent performs preliminary action by adding alloying elements (Mo, Mn, Si) during steelmaking that pre-establish the hardenability and tempering resistance properties, so that subsequent heat treatment can effectively produce the desired microstructure even in thick sections
3Strength
If alloying elements are added to improve hardenability and tempering resistance, then the strength and toughness are improved, but the manufacturing cost increases
Solution Approach 1:
The patent optimizes the parameters of alloying element content by specifying precise ranges (C: 0.02-0.08%, Mo: 0.40-1.20%, Mn: 1.50-3.00%) and their products (Mn×Mo: 0.80-2.60), achieving the required mechanical properties with controlled amounts of alloying elements rather than excessive additions
Solution Approach 2:
The patent applies local quality by having different elements perform specific functions: C and Si provide basic strength, Mn enhances hardenability, and Mo provides tempering resistance, with each element optimized at its most effective concentration range to avoid unnecessary cost from excessive alloying
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 achieves high strength (X80, X90, or X100 grade) and improved toughness and corrosion resistance, making the steel pipes suitable for severe deep-sea environments, as demonstrated by the results showing yield strength and fracture appearance transition temperature below -50°C and resistance to sulfide stress cracking.
Implementation Method 1
a process for manufacturing the same comprises hot working, quenching, and tempering
Implementation Method 2
a process for manufacturing the same comprises hot working, quenching, and tempering
Implementation Method 3
a process for manufacturing the same comprises hot working, quenching, and tempering
Data Source
AI summary
A thick-walled seamless steel pipe for line pipe which has a high strength and improved toughness and corrosion resistance in spite of the thick wall and which is suitable for use as a riser and flow line has a chemical composition comprising, in mass percent, C: 0.02-0.08%, Si: at most 0.5%, Mn: 1.5-3.0%, Al: 0.001-0.10%, Mo: greater than 0.4%-1.2%, N: 0.002-0.015%, at least one of Ca and REM in a total amount of 0.0002-0.007%, and a remainder of Fe and impurities, with the impurities having the content of P: at most 0.05%, S: at most 0.005%, and O: at most 0.005%, the chemical composition satisfying the inequality: 0.8≦[Mn]×[Mo]≦2.6, wherein [Mn] and [Mo] are the numbers equivalent to the contents of Mn and Mo, respectively, in mass percent.