Seamless Steel Pipe Composition for Sulfuric Acid Dew-Point Corrosion
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Solution Overview
Problem
Existing seamless steel pipes fail to provide adequate sulfuric acid dew-point corrosion resistance, especially in severe environments with high sulfuric acid concentrations, and lack optimal manufacturing conditions that balance corrosion resistance with manufacturability.
Innovation Solution
A seamless steel pipe with a composition of C: 0.01 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.10 to 2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010 to 0.100%, Cu: 0.03 to 0.80%, Ni: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Sb: 0.002 to 0.50%, Cr: 0.004% or less, W: 0.002% or less, and a microstructure of 50 to 65% ferrite phase, 2% or less pearlite phase, and one or both of bainite and martensitic phases, manufactured through heating to 1,100 to 1,300°C, hot rolling, normalizing heat treatment, and accelerated cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional steel compositions and manufacturing methods are used, then general manufacturability is maintained, but sulfuric acid dew-point corrosion resistance is insufficient in severe environments
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.01-0.12%, Si: 0.01-0.8%, Mn: 0.10-2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010-0.100%, Cu: 0.03-0.80%, Ni: 0.01-0.50%, Mo: 0.01-0.20%, Sb: 0.002-0.50%, Cr: 0.004% or less, W: 0.002% or less) and manufacturing process parameters (heating temperature: 1,100-1,300°C, normalizing temperature: 850-1,050°C, cooling rate: 10-50°C/s) to achieve both improved corrosion resistance and manufacturability. This systematic parameter optimization resolves the contradiction between enhanced reliability and ease of manufacture.
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases (ferrite phase: 50-65%, pearlite phase: 2% or less, and one or both of bainite and martensitic phases) through controlled alloying and heat treatment. This composite material structure combines the corrosion resistance of ferrite with the strength contributions of other phases, while the specific composition ranges ensure manufacturability, thus resolving the technical contradiction.
2Reliability
If accelerated cooling is applied to achieve desired microstructure, then sulfuric acid dew-point corrosion resistance improves, but manufacturing complexity increases
Solution Approach 1:
The patent resolves the contradiction by optimizing the cooling rate parameter within a specific range (10-50°C/s) that achieves the desired microstructure (50-65% ferrite, ≤2% pearlite, and bainite/martensite phases) without excessive manufacturing complexity. This parameter optimization balances corrosion resistance improvement with process simplicity.
Solution Approach 2:
The patent applies preliminary action through the normalizing heat treatment step performed before accelerated cooling. By pre-heating to 850-1,050°C and holding to achieve austenitization, the steel is prepared for the subsequent accelerated cooling to produce the desired microstructure. This preliminary preparation simplifies the overall manufacturing process while ensuring the target microstructure is achieved.
3Reliability
If alloying elements are added to improve corrosion resistance, then sulfuric acid dew-point corrosion resistance increases, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent applies parameter changes by establishing specific composition ranges for multiple alloying elements (C: 0.01-0.12%, Si: 0.01-0.8%, Mn: 0.10-2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010-0.100%, Cu: 0.03-0.80%, Ni: 0.01-0.50%, Mo: 0.01-0.20%, Sb: 0.002-0.50%, Cr: 0.004% or less, W: 0.002% or less) that achieve the desired corrosion resistance while maintaining reasonable compositional control. This systematic parameter specification resolves the contradiction between improved reliability and composition control complexity.
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 steel pipe achieves desirable sulfuric acid dew-point corrosion resistance with a corrosion rate of 20 mg/cm2/h or less, even in a 70% sulfuric acid environment at 50°C, while maintaining manufacturability and ensuring yield and tensile strengths suitable for piping applications.
Implementation Method 1
a structure including a ferrite phase having an area percentage of 50 to 65%, a pearlite phase having an area percentage of 2% or less, and one or both of a bainite phase and a martensitic phase representing the remainder
Implementation Method 2
heating a steel pipe material of said composition to 1,100 to 1,300°C, hot rolling the heated steel pipe material at 800°C or more into a seamless steel pipe of a predetermined shape, and cooling the seamless steel pipe to room temperature; and heating the seamless steel pipe at a normalizing temperature of 850 to 1,050°C in a normalizing heat treatment, followed by accelerated cooling
Data Source
AI summary
A seamless steel pipe of the present invention is a seamless steel pipe having a composition including, in mass %, C: 0.01 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.10 to 2.00%, P: 0.050% or less, S: 0.040% or less, Al: 0.010 to 0.100%, Cu: 0.03 to 0.80%, Ni: 0.01 to 0.50%, Mo: 0.01 to 0.20%, Sb: 0.002 to 0.50%, Cr: 0.004% or less, W: 0.002% or less, and the balance Fe and incidental impurities, and a structure including a ferrite phase having an area percentage of 50 to 65%, a pearlite phase having an area percentage of 2% or less, and one or both of a bainite phase and a martensitic phase representing the remainder, the seamless steel pipe having a yield strength of 230 MPa or more, and a tensile strength of 380 MPa or more.