ERW Thick-Walled Steel Pipe Structure for Deep-Well Casing Circularity
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Solution Overview
Problem
Conductor casings for deep-well oil or gas wells face issues with breakage due to bending deformation and require high strength to withstand weight, with existing technologies failing to ensure sufficient circularity and maintaining strength after post-weld heat treatment.
Innovation Solution
A high-strength thick-walled electric-resistance-welded steel pipe with a circularity of 0.6% or less, composed of a bainitic ferrite phase with fine Nb precipitates and specific chemical composition, is manufactured using continuous rolling and in-line heat treatment to reduce linear misalignment and maintain strength after heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional UOE steel pipe joining method is used, then connector strength is achieved, but linear misalignment occurs reducing circularity
Solution Approach 1:
The invention merges the steel pipe and connector into a single integrated component manufactured by continuous forming. This eliminates the separate joining process that causes linear misalignment, achieving both high strength (API X80 grade) and high circularity (0.6% or less) simultaneously through unified manufacturing.
Solution Approach 2:
The electric-resistance-welded steel pipe structure serves multiple functions: it provides the required mechanical strength, maintains high circularity for reduced stress concentration, and enables continuous manufacturing. The integrated design makes the single component fulfill all requirements that previously required separate pipe and connector parts.
2Reliability
If post-weld heat treatment is applied to relieve residual stress, then hydrogen cracking is prevented, but strength decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the steel to specific ranges (C: 0.02-0.18%, Si: 0.05-0.50%, Mn: 1.00-2.00%, Cr: 0.30-1.00%, Ti: 0.005-0.030%, Nb: 0.060% or less) that enable the material to maintain high strength after post-weld heat treatment. The controlled composition prevents excessive softening while still allowing stress relief.
Solution Approach 2:
The invention uses a composite microstructure consisting of bainitic ferrite (90% or more by volume) with fine Nb precipitates dispersed throughout. This composite structure provides both the toughness needed for stress relief treatment and the strength retention capability, as the fine precipitates prevent excessive grain growth and softening during heat treatment.
3Manufacturing precision
If additional circularity improvement steps are added, then linear misalignment is reduced, but productivity decreases
Solution Approach 1:
The invention performs circularity optimization during the continuous forming process itself, before the pipe is completed. The forming rolls are designed to produce the final high-circularity shape (0.6% or less) directly during manufacturing, eliminating the need for subsequent cutting or straightening operations that would reduce productivity.
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 solution provides a conductor casing with high strength and toughness, resisting breakage during placement and maintaining API X80 grade strength even after post-weld heat treatment, thus reducing manufacturing costs and improving productivity.
Implementation Method 1
electric-resistance-welded steel pipe
Implementation Method 2
a structure composed of 90% or more by volume of a bainitic ferrite phase as a main phase
Implementation Method 3
the structure containing fine Nb precipitates having a particle size of less than 20 nm dispersed in a base material portion
Data Source
AI summary
A high-strength high-toughness electric-resistance-welded steel pipe having high resistance to post-weld heat treatment is provided. The steel pipe having a composition including C: 0.01% to 0.12%, Si: 0.05% to 0.50%, Mn: 1.0% to 2.2%, P: 0.03% or less, S: 0.005% or less, Al: 0.001% to 0.10%, N: 0.006% or less, Nb: 0.010% to 0.100%, and Ti: 0.001% to 0.050%. The steel pipe having a structure composed of 90% or more by volume of a bainitic ferrite phase and 10% or less (including 0%) by volume of a second phase. The bainitic ferrite phase having an average grain size of 10 μm or less, and the structure containing fine Nb precipitates having a particle size of less than 20 nm dispersed in a base material portion. The steel pipe having high strength and toughness that is maintained through post-weld heat treatment, including heating to a temperature of 600° C. or more.