Seamless Steel Tube Composition for Dual-Side Corrosion Resistance
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Solution Overview
Problem
Seamless steel pipes used in environments where the outer surface is exposed to sulfuric acid corrosion and the inner surface is exposed to high-temperature water exhibit inadequate corrosion resistance.
Innovation Solution
A seamless steel pipe with a specific chemical composition and metallographic structure, including controlled grain sizes and densities of MnS and MnS-oxide inclusions, enhances corrosion resistance. The composition includes C: 0.06% or less, Si: 0.55% or less, Mn: 0.70 to 1.40%, P: 0.020% or less, S: 0.0005 to 0.020%, N: 0.005% or less, O: 0.0005 to 0.0035%, Cu: 0.25 to 0.45%, Ni: 0.50% or less, Mo: 0.20% or less, and Sb: 0.05 to 0.15%, with a ferrite area fraction of 90% or more and controlled MnS and MnS-oxide densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional welding or flanging methods are used to connect steel tubes, then the steel tube structure can be assembled, but discontinuities are introduced that reduce fatigue strength and may cause stress concentration leading to brittle fracture
Solution Approach 1:
The patent applies continuous hot rolling to form seamless steel tubes, eliminating discontinuities introduced by welding or flanging. The continuous manufacturing process ensures uniform microstructure and eliminates weak points, thereby maintaining high fatigue strength and preventing stress concentration that could lead to brittle fracture.
Solution Approach 2:
The patent utilizes controlled plastic deformation during hot rolling, changing the microstructural parameters of the steel. By controlling temperature, pressure, and deformation rate during the rolling process, the steel achieves optimized grain structure and mechanical properties, improving both strength and reliability.
2Strength
If alloying elements are added to improve steel strength, then tensile strength increases, but manufacturing complexity and cost increase
Solution Approach 1:
The patent achieves high strength through controlled plastic deformation and microstructural refinement during hot rolling rather than relying heavily on alloying. By optimizing rolling parameters (temperature, pressure, deformation rate), the steel develops a fine-grained microstructure that provides high strength with minimal alloy additions, thereby reducing manufacturing complexity.
Solution Approach 2:
The patent creates a composite microstructure through controlled phase transformation during cooling after hot rolling. The resulting microstructure contains multiple phases (ferrite, pearlite, bainite, or martensite) that work together to provide high strength, eliminating the need for complex alloy compositions.
3Manufacturing precision
If hot rolling temperature is increased to improve plasticity and eliminate defects, then manufacturing quality improves, but energy consumption increases
Solution Approach 1:
The patent optimizes the hot rolling temperature within a specific range (above austenite transformation temperature but not excessively high) to achieve the necessary plasticity for defect elimination. By precisely controlling temperature parameters and combining them with controlled plastic deformation, the process achieves high manufacturing quality while minimizing energy consumption compared to excessive heating.
Solution Approach 2:
The continuous hot rolling process maintains the steel in the austenite phase throughout the deformation zone, ensuring continuous plastic flow and defect elimination without interruption. This continuous action improves quality efficiently by eliminating the need for repeated heating and processing cycles.
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 environments with sulfuric acid exposure on the outer surface and high-temperature water exposure on the inner surface, improving mechanical properties and reducing corrosion initiation points.
Implementation Method 1
the steel tube having an inner surface and an outer surface, the steel tube being capable of trapping a heat generating agent within the steel tube such that the heat generating agent is retained within the steel tube thereby preventing loss of heat
Data Source
AI summary
A seamless steel pipe having an inner surface and an outer surface, having a chemical composition including, by mass, C: 0.06% or less, Si: 0.55% or less, Mn: 0.70-1.40%, P: 0.020% or less, S: 0.0005-0.020%, N: 0.005% or less, O: 0.0005-0.0035%, Cu: 0.25-0.45%, Ni: 0.50% or less, Mo: 0.20% or less, and Sb: 0.05-0.15%, with the balance being Fe and impurities, and having a metallographic structure including, by area%, ferrite: 90.0% or more, wherein the average crystal grain size of the ferrite in the inner surface layer of the pipe is 3.0-20.0 µm, and that in the outer surface layer of the pipe is 3.0-25.0 µm, and wherein the inner surface layer and the outer surface layer contain MnS and MnS-oxide, the number density of MnS is less than 100/mm2, and the ratio of the number density of MnS-oxide relative to that of MnS is 0.10 or more.