Seamless Steel Pipe Quenching and Tempering for Submarine Flow Lines
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for manufacturing thick wall seamless steel pipes with high strength and toughness for submarine flow lines face challenges in achieving sufficient performance, particularly in energy efficiency and production cost, due to issues with coarse-grained crystal formation and reduced cooling rates during inline heat treatment.
Innovation Solution
The method involves quenching and tempering of steel pipes with specific chemical compositions and microstructures, including controlling the volume ratio of mixed microstructures like martensite and austenite, and optimizing cooling rates to achieve a balance between strength and toughness, using a process that includes hot rolling, holding at transformation points, and forced cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If inline heat treatment with quenching directly after finish rolling is used, then energy consumption is reduced and manufacturing efficiency is improved, but coarse-grained crystal structure forms resulting in poor toughness and corrosion resistance
Solution Approach 1:
The heat treatment process is segmented into two distinct stages: (1) quenching from finish rolling temperature to obtain martensitic structure, and (2) subsequent heating to Ac1 transformation point to form tempered martensite. This segmentation allows each stage to serve its specific purpose - the first for strength and the second for toughness - thereby resolving the contradiction between energy efficiency and material performance.
Solution Approach 2:
The invention changes the temperature parameter through a two-stage process: first maintaining high temperature during quenching, then heating to a specific range (Ac1 transformation point) for tempering. This parameter change enables the steel to transform from a brittle as-quenched state to a tough tempered state, solving the contradiction between energy consumption and toughness.
2Manufacturing precision
If the time from finish rolling to reheating is extended to cool the steel pipe to low temperature, then fine-grained crystal structure is achieved, but production efficiency is significantly reduced
Solution Approach 1:
The invention performs preliminary quenching action immediately after finish rolling to establish the martensitic structure before any significant cooling occurs. This preliminary action eliminates the need for extended cooling time, as the subsequent tempering process is much faster than natural cooling, thereby maintaining both fine grain structure and high production efficiency.
Solution Approach 2:
The invention skips the intermediate cooling step by directly heating the as-quenched pipe to the Ac1 transformation point. This rushing through of the process eliminates time-consuming intermediate cooling while achieving the desired microstructure, resolving the contradiction between grain size control and production efficiency.
3Device complexity
If the cooling rate is reduced for thick wall pipes, then manufacturing complexity is reduced, but the steel pipe fails to achieve sufficient toughness
Solution Approach 1:
The invention changes the temperature parameter by heating the pipe to the Ac1 transformation point after quenching. This parameter change enables the formation of tempered martensite structure that provides sufficient toughness even with reduced cooling rates, resolving the contradiction between manufacturing complexity and toughness.
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 enables the production of seamless steel pipes with high yield strength and excellent toughness, suitable for thick wall applications, while maintaining energy efficiency and reducing production costs.
Implementation Method 1
quenching a pipe without cooling to room temperature after making in a pipe is introduced
Implementation Method 2
a process of quenching a pipe without cooling to room temperature after making in a pipe
Implementation Method 3
the steel pipe does not undergo the transformation and reverse transformation process
Implementation Method 4
the steel pipe does not undergo the transformation and reverse transformation process
Data Source
AI summary
The present invention relates to the following seamless steel pipes excellent in strength, toughness and weldability, particularly suitable for submarine flow lines, and a manufacturing method thereof. An as-quenched seamless steel pipe having a chemical composition consisting of, by mass%, C: 0.03 to 0.08%, Mn: 0.3 to 2.5%, Al: 0.001 to 0.10%, Cr: 0.02 to 1.0%, Ni: 0.02 to 1.0%, Mo: 0.02 to 0.8%, Ti: 0.004 to 0.010%, N: 0.002 to 0.008%, Ca: 0.0005 to 0.005%, and the balance Fe and impurities, with not more than 0.25% of Si, not more than 0.05% of P, not more than 0.005% of S, less than 0.005% Nb, and less than 0.0003% of B as the impurities, and having a microstructure consisting of not more than 20 volume% of polygonal ferrite, not more than 10 volume% of a mixed microstructure of martensite and retained austenite, and balance bainite. B can be 0.0003 to 0.001%. Mg and/or REM can be contained. The manufacturing method is characterized by the cooling rate during quenching.