Seamless Pipe Inner Surface Carburizing Prevention
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Solution Overview
Problem
Existing methods for producing seamless pipes using the mandrel mill method struggle to effectively inhibit carburizing on the inner surface, leading to anomalous hardened portions and reduced corrosion resistance, with previous solutions being costly or impractical due to excessive graphite usage, abrasive removal methods, or undefined oxidizing gas requirements.
Innovation Solution
A method involving the application of a lubricant to a mandrel bar, followed by reheating the pipe in a furnace where an oxidizing gas is fed at a controlled flow rate, specifically determined by the equation Q≥7.7394×10^12·exp(-22748(T∞+Tp)×0.5+273)·CinTin+273·1ρc·Ab·π·Dp·Lp, to oxidize carbon at the inner surface, preventing carburizing while minimizing gas usage and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If graphite lubricant is applied to the mandrel bar to enable drawing and rolling, then the mandrel mill operation is feasible, but carburizing occurs on the inner surface of the pipe
Solution Approach 1:
The patent converts the harmful carburizing effect into a beneficial decarburization process by introducing oxidizing gas during reheating. The carbon from the graphite lubricant that would normally cause carburizing is instead oxidized and removed from the pipe inner surface, transforming the harmful carbon deposition into a useful carbon removal process that prevents inner surface carburizing while maintaining the lubrication function.
Solution Approach 2:
The patent changes the chemical atmosphere parameters during the reheating process by introducing oxidizing gas (such as air or oxygen-enriched atmosphere). This parameter change from a reducing or neutral atmosphere to an oxidizing atmosphere fundamentally alters the chemical reactions at the pipe inner surface, preventing carbon diffusion into the steel and instead promoting carbon oxidation and removal.
2Object-affected harmful factors
If oxidizing gas is fed into the material pipe in the reheating furnace to inhibit carburizing, then carburizing is prevented, but the required flow rate and temperature control are not clearly defined leading to increased costs
Solution Approach 1:
The patent establishes specific parameter ranges for oxidizing gas flow rate and temperature to optimize the decarburization process. By defining these parameters quantitatively, the patent transforms an undefined complex control problem into a manageable process with clear operating windows, reducing trial-and-error and associated costs while effectively preventing inner surface carburizing.
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 inhibits carburizing on the inner surface of seamless pipes by oxidizing carbon at controlled temperatures, reducing production and facility costs, and ensuring uniform cooling, thus enhancing the quality and cost-effectiveness of the seamless pipe production process.
Implementation Method 1
an oxidizing gas is fed into the material pipe or tube when a temperature of the material pipe or tube is 550° C. or higher and 1000° C. or lower in the reheating step
Data Source
AI summary
A production method of a seamless pipe or tube according to the present invention comprises the steps of applying a lubricant containing carbon to a mandrel bar, producing a material pipe or tube with a mandrel mill using the mandrel bar to which the lubricant is applied, and reheating the material pipe or tube in a reheating furnace, wherein when a temperature of the material pipe or tube is 550° C. or higher and 1000° C. or lower in the reheating step, an oxidizing gas is fed into the material pipe or tube.