Hot Coil Line Pipe Strength Deviation Reduction
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Solution Overview
Problem
Hot coils used in line pipe production face challenges in reducing deviation in ordinary temperature strength and improving low temperature toughness due to the coiling step, which restricts production conditions and results in inadequate steel structure uniformity.
Innovation Solution
The production method involves achieving an effective crystal grain size of 2 to 10 µm and a matrix structure with a bainite and acicular ferrite area ratio of 60 to 99%, with multiple stage cooling and recrystallization temperature range stops during hot rolling, to ensure uniformity and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hot rolled steel plate is wound in a coil shape for spiral steel pipe or electric resistance welded steel pipe production, then field installation ability is improved, but deviation in ordinary temperature strength increases and low temperature toughness deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the cooling rate (10-50°C/s) and holding temperature (500-700°C) during hot rolling, as well as controlling the finish rolling temperature (700-900°C). These parameter adjustments enable the formation of a uniform fine-grained structure with 60-90% acicular ferrite, thereby reducing strength deviation and improving low-temperature toughness while maintaining the coiled shape for field installation.
Solution Approach 2:
The patent implements local quality by ensuring uniform microstructure distribution throughout the steel plate thickness and width. Through controlled cooling and holding processes, the entire coil achieves consistent acicular ferrite content (60-90%), eliminating local variations in strength that typically occur in coiled products. This uniformity ensures both reduced strength deviation and improved toughness across the entire material.
2Reliability
If multiple stage cooling is applied to hot coils, then low temperature toughness is improved, but production condition restrictions increase
Solution Approach 1:
The patent merges the cooling process with the rolling process by implementing cooling during the finish rolling stage and immediately followed by holding at 500-700°C. This combined approach achieves the desired acicular ferrite structure (60-90%) and improved low-temperature toughness without requiring separate, complex cooling equipment or multiple distinct process stages, thereby reducing production condition restrictions.
3Manufacturing precision
If hot rolled steel plate is used without coiling for UOE method, bending roll method, or JCOE method, then steel structure uniformity is improved, but field installation ability deteriorates
Solution Approach 1:
The patent applies parameter changes by controlling the finish rolling temperature (700-900°C) and implementing rapid cooling (10-50°C/s) followed by holding at 500-700°C. These parameter adjustments create a uniform fine-grained structure with 60-90% acicular ferrite throughout the coiled steel plate, achieving the same steel structure uniformity as non-coiled plates while maintaining the coiled shape for improved field installation ability.
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 results in a hot coil with reduced deviation in ordinary temperature strength and enhanced low temperature toughness, meeting API standards for line pipes used in long-distance transport.
Implementation Method 1
cooling the steel plate after hot rolling in multiple stages
Implementation Method 2
holding the steel plates at the recrystallization temperature range between the rough rolling and finish rolling
Data Source
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AI summary
The present invention provides a hot coil for line pipe use which can reduce deviation in ordinary temperature strength and improve low temperature toughness despite the numerous restrictions in production conditions due to the coiling step and provides a method of production of the same, specifically makes the steel plate stop for a predetermined time between rolling passes in the recrystallization temperature range and performs cooling by two stages after hot rolling so as to thereby make the steel structure at the center part of plate thickness and effective crystal grain size of 3 to 10 µm, make the total of the area ratios of bainite and acicular ferrite 60 to 99%, and make the absolute value of A-B 0 to 30% when the totals of the area ratios of bainite and acicular ferrite at any two portions are designated as respectively A and B.