ERW Steel Pipe Microstructure for Sulfide Stress Cracking Resistance
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Solution Overview
Problem
Existing high-strength steel pipes or tubes for line pipes face challenges in achieving sufficient sulfide stress corrosion cracking (SSC) resistance due to excessive surface hardness and uneven cooling rates during thermo-mechanical control processing, which leads to increased shear residual stress.
Innovation Solution
Control the shear residual stress on the surface of the steel pipe or tube by maintaining specific microstructural properties, including a total volume fraction of ferrite and bainite, average crystal grain size, and residual stress levels, along with controlled chemical compositions to enhance SSC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If TMCP technology with accelerated cooling is used to increase cooling rate, then strength is improved, but surface hardness increases excessively and SSC resistance decreases
Solution Approach 1:
The patent applies local quality by creating different microstructural zones within the steel sheet - the center maintains a microstructure with 90-99% ferrite and bainite for high SSC resistance, while the surface layer (0.1mm from surface) has 95-99% ferrite and bainite for controlled hardness. This spatial differentiation of microstructural properties resolves the contradiction between overall strength and surface SSC resistance.
Solution Approach 2:
The patent changes the cooling rate parameter spatially - using a controlled average cooling rate of 10-60°C/s at the sheet center to prevent excessive hardness, while allowing faster cooling at the surface. This parameter modification enables achieving both strength and SSC resistance requirements.
2Strength
If higher strength steel material is used, then transportation efficiency is improved, but SSC resistance decreases
Solution Approach 1:
The patent creates local quality differences between the steel sheet center and surface layers. The center region (where tensile stress concentrates) has optimized microstructure with 90-99% ferrite and bainite for high strength, while the surface layer has 95-99% ferrite and bainite for low hardness and high SSC resistance. This resolves the contradiction between overall strength and surface corrosion resistance.
Solution Approach 2:
The patent transitions from considering only bulk material properties to incorporating spatial dimension - specifically the radial position within the sheet thickness. By defining different microstructural requirements at different radial positions (center vs. 0.1mm from surface), the patent achieves both high strength and high SSC resistance through dimensional differentiation.
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 results in a high-strength electric resistance welded steel pipe or tube with excellent SSC resistance, characterized by specific microstructural and chemical requirements, ensuring no cracks and reduced pitting corrosion.
Implementation Method 1
in a steel microstructure at a wall thickness center of the base metal portion, a total volume fraction of ferrite and bainite is 90% or more
Implementation Method 2
an absolute value of circumferential residual stress on a pipe or tube inner surface of the electric resistance welded steel pipe or tube is 10 MPa or more, an absolute value of shear residual stress on the pipe or tube inner surface is 300 MPa or less
Data Source
AI summary
Provided is a high-strength electric resistance welded steel pipe or tube having excellent SSC resistance. An absolute value of circumferential residual stress on a pipe or tube inner surface of the electric resistance welded steel pipe or tube is 10 MPa or more, and an absolute value of shear residual stress on the pipe or tube inner surface is 300 MPa or less. In a steel microstructure at a wall thickness center of a base metal portion of the electric resistance welded steel pipe or tube, a total volume fraction of ferrite and bainite is 90% or more and an average crystal grain size is 9.0 um or less. In a steel microstructure at a position 0.1 mm radially outward from the pipe or tube inner surface of the base metal portion, a total volume fraction of ferrite and bainite is 95% or more.