Martensitic Stainless Steel Pipe Composition for High Strength and Toughness
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Solution Overview
Problem
Conventional 13Cr-type martensitic stainless steel pipes used in oil and gas wells suffer from inferior toughness at high strength levels, limiting their application due to the need for expensive Ni and Mo additions and increased phosphorus reduction costs, which complicates industrial production.
Innovation Solution
A high-strength martensitic stainless steel pipe composition with controlled C, Mn, N, and Al levels to minimize grain boundary carbides, combined with strategic use of Nb, Mo, and V to enhance tempering temperature, allowing for excellent toughness and hot workability without excessive Ni and Mo, and reduced phosphorus content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength (95 ksi grade or more) is achieved using conventional API-13Cr material, then strength is improved, but toughness deteriorates significantly
Solution Approach 1:
The invention changes the chemical composition parameters by strictly controlling P content (0.008% or less), C content (0.18-0.22%), and Al content (0.0005-0.003%), while optimizing Mn (0.40-1.00%) and N (0.012-0.040%) to achieve both high strength and satisfactory toughness simultaneously
Solution Approach 2:
The invention creates a composite effect by combining multiple elements (Cr, Mn, Ni, Al, N, Cu, Ti, V, Mo, Nb, B, Ca) in specific proportions to form a martensitic structure that provides both high strength and toughness, rather than relying on a single element
2Reliability
If P content is reduced to less than 0.008% to improve toughness, then toughness is improved, but production cost increases due to increased dephosphorization frequency
Solution Approach 1:
The invention optimizes the parameter combination of C (0.18-0.22%), Mn (0.40-1.00%), Al (0.0005-0.003%), and N (0.012-0.040%) to achieve satisfactory toughness at P content of 0.008% or less, reducing the need for excessive dephosphorization while maintaining required mechanical properties
3Reliability
If expensive elements Ni and Mo are added in large quantities to ensure toughness and corrosion resistance, then toughness and corrosion resistance are improved, but material cost increases
Solution Approach 1:
The invention optimizes the parameter combination of Cr (11.50-13.50%), Mn (0.40-1.00%), Ni (0.5% or less), Al (0.0005-0.003%), N (0.012-0.040%), Cu (0.25% or less), Ti (0.05% or less), V (0.02-0.18%), Mo (0 to 0.05%), Nb (0 to 0.009%), B (0.0010% or less), and Ca (0.0050% or less) to achieve both high toughness and cost-effectiveness by minimizing expensive alloy additions
4Shape
If straightening treatment is performed after tempering to improve straightness, then shape is improved, but toughness deteriorates due to additional work hardening
Solution Approach 1:
The invention optimizes the parameter combination of V (0.02-0.18%), Mo (0 to 0.05%), and Nb (0 to 0.009%) to raise the tempering temperature to 610-750°C, which suppresses work hardening during subsequent straightening treatment and maintains toughness while achieving the required straightness
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 cost-effective, high-strength martensitic stainless steel pipe with improved toughness and hot workability, suitable for oil and gas well environments, without the need for expensive alloy additions and with reduced production costs, ensuring stability and efficiency in industrial production.
Implementation Method 1
a martensitic stainless steel pipe... having a yield strength of 650 MPa or more and a toughness exceeding 70 J/cm2 by impact value in the Charpy impact test at 0 degrees C. using V-notch test pieces
Implementation Method 2
heating the steel pipe... at a temperature T1, which exists in the temperature range of 930 to 980 degrees C. for 5 to 30 minutes; then cooling the steel pipe from the temperature T1 to a temperature T2
Data Source
AI summary
A martensitic stainless steel pipe, which comprises specified quantities of C, Si, Mn, P, S, Cr, Ni, Al, N, Cu, Ti, V, Mo, Nb, B and Ca, and the balance being Fe and impurities, has satisfactory toughness at a high strength of 650 MPa or more by yield strength and also excellent hot workability. Therefore, it can be used as a high-strength martensitic stainless steel pipe for carbon dioxide gas corrosion resistant use, to be used in oil and/or gas well environments containing no hydrogen sulfide but carbon dioxide gas. This high-strength martensitic stainless steel pipe is an inexpensive martensitic stainless steel pipe, which does not require an addition of large quantities of expensive elements such as Ni and Mo, and moreover does not require the control of the content of P to a value less than 0.010% by mass.