Seamless Steel Pipe HIC Resistance via Inclusion Control
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Solution Overview
Problem
Seamless steel pipes used in oil wells, particularly those with a yield strength of 110 ksi grade, face challenges in hydrogen-induced cracking (HIC) resistance in sour environments, with limited studies and ineffective solutions available to enhance their HIC resistance.
Innovation Solution
A seamless steel pipe with a specific chemical composition and a predicted maximum major axis of inclusions of 150 μm or less, determined through extreme value statistical processing, which enhances HIC resistance by reducing stress concentration at inclusion interfaces, thereby improving the material's resistance to cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the yield strength of seamless steel pipes is enhanced to 110 ksi grade for deep well applications, then the strength parameter is improved, but the HIC resistance deteriorates due to increased susceptibility to hydrogen-induced cracking in sour environments
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.18-0.35%, Si: 0.10-0.30%, Mn: 0.40-0.80%, Cr: 0.30-0.80%, Mo: 0.50-1.00%, B: 0.0005-0.0030%) and microstructural parameters (prior-austenite grain size No. 8.5 or higher, tempered martensite as main phase, specific carbide distribution) to achieve the optimal balance between high yield strength (110 ksi grade) and HIC resistance in sour environments
Solution Approach 2:
The patent creates a composite microstructure consisting of tempered martensite as the main phase with dispersed carbides (M3C, M2C, M23C6, MC types) and controlled inclusions, where each component contributes to both strength and HIC resistance. The复合 microstructure achieves synergistic effects: tempered martensite provides high strength, while the dispersed carbides and controlled inclusions reduce stress concentration and improve hydrogen embrittlement resistance
2Strength
If alloying elements are added to enhance strength, then the strength parameter is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent applies multi-functionality by selecting alloying elements that simultaneously contribute to multiple properties: Cr and Mo enhance both strength and corrosion resistance in sour environments, B improves hardenability and refines grain structure, Si and Mn contribute to both strength and deoxidation. This multi-functional approach achieves high strength and HIC resistance without requiring excessive alloying or complex processing
Data Source
AI summary
The seamless steel pipe according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.070%, Cr: 0.30 to 1.50%, Mo: 0.25 to 2.00%, Ti: 0.002 to 0.020%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, rare earth metal: 0.0001 to 0.0015%, Ca: 0.0001 to 0.0100%, N: 0.0100% or less and O: 0.0020% or less, with the balance being Fe and impurities, and satisfying Formula (1) described in the description. A predicted maximum major axis of inclusions is 150 μm or less, the predicted maximum major axis being predicted by means of extreme value statistical processing. The yield strength is within a range of 758 to 862 MPa.