Electric Resistance Welded Steel Pipe Yield Ratio Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing electric resistance welded steel pipes struggle to maintain a low yield ratio after heating the coating, leading to instability in deformation characteristics and potential buckling or fracture during pipeline laying, especially due to strain aging caused by pipe-making and heating processes.
Innovation Solution
The method involves hot rolling a steel slab with reduced Nb content, coiling it at a specific temperature to precipitate Nb carbides, forming it into a pipe, and then tempering it within a controlled temperature range to further precipitate solute carbon and Nb carbides, which pins dislocations and reduces yield strength more than tensile strength, thereby maintaining a low yield ratio and improving strain aging resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pipe is coiled over a spool and then uncoiled for laying, then the efficiency of submarine line pipe laying is improved, but the pipe is subjected to tensile and compressive stresses due to bending and unbending, which may cause local buckling or pipe fracture
Solution Approach 1:
The invention changes the material parameters by precisely controlling the chemical composition (C: 0.05-0.10%, Si: 0.05-0.50%, Mn: 1.00-2.00%, Nb: 0.005-0.050%, Ti: 0.005-0.050%, V: 0.005-0.100%) and applying specific heat treatment parameters (tempering at 150-250°C for 5-30 minutes after accelerated cooling) to achieve a yield ratio of 85% or less, enabling the pipe to withstand bending stresses during reel barge laying
Solution Approach 2:
The invention utilizes phase transition during accelerated cooling to transform the microstructure into a fine-grained structure with precipitated carbides, which provides the necessary deformation resistance while maintaining a low yield ratio to prevent buckling during the coiling and uncoiling process
2Reliability
If Nb+V+Ti are limited to 0.040% or less to prevent softening at the heat affected zone, then the yield ratio of the weld zone can be made 85% or less, but the pipe-making strain and subsequent heating cause strain aging that raises the yield strength
Solution Approach 1:
The invention performs preliminary action by applying accelerated cooling and tempering treatment before the pipe-making strain and coating heating occur. This pre-treatment fixes the microstructure and precipitates carbides in advance, creating a stable base that resists subsequent strain aging, thereby maintaining low yield ratio even after all processing steps
Solution Approach 2:
The invention changes the material parameters by optimizing the chemical composition with specific ranges of alloying elements and controlling the heat treatment parameters (accelerated cooling followed by tempering at 150-250°C for 5-30 minutes) to achieve a microstructure that is resistant to strain aging, maintaining yield ratio of 85% or less even after pipe-making and coating heating
3Strength
If the pipe is made with sufficient strength to withstand high internal pressure, then the circumferential strength is improved, but the deformation resistance against axial strain deteriorates due to high yield ratio
Solution Approach 1:
The invention changes the material parameters by precisely controlling the chemical composition (particularly C: 0.05-0.10%, Si: 0.05-0.50%, Mn: 1.00-2.00%, Nb: 0.005-0.050%) and applying specific heat treatment parameters (accelerated cooling followed by tempering at 150-250°C for 5-30 minutes) to achieve a unique microstructure that provides both high circumferential strength and low yield ratio for axial deformation resistance
Solution Approach 2:
The invention creates a composite microstructure through accelerated cooling and tempering that combines fine-grained ferrite with precipitated carbides (NbC, TiC, VC), achieving a material structure that simultaneously provides high strength for internal pressure resistance and low yield ratio for axial deformation resistance
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
This approach effectively suppresses the rise in yield ratio due to heating, ensuring excellent deformation characteristics and strain aging resistance, making the steel pipes suitable for pipeline applications by reducing the amount of Nb to less than 0.02% and tempering after pipe-making.
Implementation Method 1
coiling it at a specific temperature to precipitate Nb carbides, forming it into a pipe, and then tempering it within a controlled temperature range to further precipitate solute carbon and Nb carbides, which pins dislocations and reduces yield strength more than tensile strength
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method of production of electric resistance welded steel pipe which is low in yield ratio and is excellent in aging resistance characteristics, characterized by hot rolling a steel slab which contains C: 0.03 to 0.12%, Si: 0.03 to 0.5%, Mn: 0.5 to 2.0%, P: 0.03% or less, S: 0.003% or less, Al: 0.10% or less, Nb: 0.003% to less than 0.02%, Ti: 0.005 to 0.03%, and N: 0.006% or less, which satisfies Ti>3.4N and weld cracking parameter Pcm (%)≤0.21, and which has a balance of Fe and unavoidable impurities, coiling the hot rolled steel plate at 600°C or less, then working this hot rolled steel plate to a pipe shape and welding the abutting faces by electric resistance welding to thereby obtain electric resistance welded steel pipe, and heating this electric resistance welded steel pipe at a heating temperature of 400 to 720°C in range.