Seamless Steel Pipe Cooling Line for Heavy-Wall Toughness
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Solution Overview
Problem
Conventional methods struggle to manufacture heavy-walled seamless steel tubes with excellent low-temperature toughness, as the microstructure at the wall thickness center portion tends to become coarse, leading to deteriorated toughness, and existing solutions do not effectively address wall thicknesses exceeding 12.7mm.
Innovation Solution
An equipment line is developed where a cooling system is placed between the heating and piercing devices, allowing for accelerated cooling at a rate of 1.0°C/s or more, followed by hot working, to create a non-equilibrium microstructure with a high ferrite phase ratio, enhancing low-temperature toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional hot working is used to manufacture heavy-walled seamless steel tubes, then the wall thickness can be increased, but the microstructure at the wall thickness center portion becomes coarse leading to deteriorated toughness
Solution Approach 1:
The patent applies preliminary accelerated cooling before hot working to create a fine-grained microstructure in advance. By cooling the steel ingot at a rate of 1.0°C/s or more before piercing and rolling, the austenite grains are refined, which prevents coarse microstructure formation at the wall thickness center even during subsequent heavy-walled tube manufacturing processes
Solution Approach 2:
The patent changes the cooling rate parameter from conventional slow cooling to accelerated cooling (1.0°C/s or more). This parameter change transforms the microstructure development process, preventing grain coarsening that would normally occur during conventional hot working of heavy-walled tubes
2Strength
If accelerated cooling at 1.0°C/s or more is applied to create fine microstructure, then low-temperature toughness is improved, but additional cooling equipment and process complexity are required
Solution Approach 1:
The cooling system is designed to serve multiple functions: it cools the steel ingot during solidification, performs accelerated cooling to refine grains, and prepares the material for subsequent hot working. This multi-functionality reduces the need for separate specialized equipment for each process stage
3Strength
If minimum hot working is applied to maintain microstructure, then low-temperature toughness is improved, but manufacturing flexibility and adaptability are reduced
Solution Approach 1:
The patent establishes specific parameter ranges for hot working (temperature and deformation amount) that maintain the fine microstructure while allowing sufficient manufacturing flexibility. By defining these parameter windows, the process can be adapted to different steel grades and product specifications without compromising 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 heavy-walled stainless seamless steel tubes with improved low-temperature toughness and high yield strength, maintaining excellent corrosion resistance even at the wall thickness center portion, while minimizing hot working and maintaining industrial feasibility.
Implementation Method 1
wherein the heated steel is cooled within a proper temperature range and thereafter hot working is applied to the cooled steel
Implementation Method 2
an equipment line wherein a heating device (1), a cooling system (4) and a piercing device (2) are arranged in this order
Implementation Method 3
a piercing device (2) which pierces the heated steel into a hollow steel tube
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Provided is an equipment line for manufacturing a seamless steel tube and a method of manufacturing a heavy-walled high-strength stainless seamless steel tube for oil wells having excellent low-temperature toughness using the equipment line. In the equipment line where a heating device, a piercing device and a rolling mill are arranged, a cooling system is further arranged between the heating device and the piercing device or between the piercing device and the rolling mill. A thermostat may be arranged on an exit side of the rolling mill. Using the equipment line, a heated steel having a stainless steel chemical composition or a hollow steel tube formed by piercing the heated steel is cooled by accelerated cooling to a cooling stop temperature of 600°C or above at an average cooling rate of 1.0°C/s or more thus allowing the hollow steel tube to have a phase distribution in a non-equilibrium state and, immediately thereafter, the hollow steel tube is formed into a seamless tube having a predetermined size. Accordingly, the microstructure can become extremely fine even when a hot working amount is small so that the heavy-walled steel tube can ensure excellent low-temperature toughness even at the wall thickness center portion whereby a heavy-walled high-strength stainless seamless steel tube having excellent low-temperature toughness can be manufactured easily at a low cost.