Seamless Steel Pipe Microstructure for Sour-Service SSC Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing high-strength seamless steel pipes for oil and gas wells lack sufficient sulfide stress corrosion cracking resistance (SSC resistance) in sour environments, particularly in terms of achieving a high and stable KILIMIT value.
Innovation Solution
A high-strength seamless steel pipe with a yield strength of 758 MPa or more and a KILIMIT value of 23.0 MPa√m or more, achieved through a manufacturing process involving specific composition ranges, intermediate cooling, and reheating quenching and tempering, to refine the steel microstructure and enhance SSC resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional high-strength seamless steel pipes are used to meet strength requirements, then yield strength is achieved, but sulfide stress corrosion cracking resistance (KILIMIT value) is insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling chemical composition parameters (C: 0.20-0.35%, Cr: 0.50-1.50%, Mo: 0.10-1.00%, B: 0.0005-0.0050%) and heat treatment parameters (austenite formation temperature, cooling rate, tempering temperature) to simultaneously achieve high yield strength (≥758 MPa) and high KILIMIT value (≥23.0 MPa√m), resolving the contradiction between strength and corrosion resistance
Solution Approach 2:
The patent creates a composite microstructure consisting of martensite as the primary phase with controlled carbide precipitates (MC-type, M23C6-type, M6C-type) distributed throughout. This composite structure at the micro level provides both the strength from martensite and the corrosion resistance from the controlled carbide distribution, achieving both requirements simultaneously
2Strength
If alloying elements are added to improve strength, then yield strength increases, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes the parameter ranges of alloying elements to achieve the desired properties within controlled limits. By specifying precise ranges for C, Cr, Mo, and B, the patent balances strength enhancement with manufacturing feasibility, avoiding excessive complexity while achieving yield strength ≥758 MPa and KILIMIT ≥23.0 MPa√m
Solution Approach 2:
The patent incorporates alloying elements during the initial steelmaking process, performing the composition adjustment in advance before rolling and heat treatment. This preliminary action simplifies the overall manufacturing process by integrating composition control into the base production流程, rather than requiring additional complex processing steps later
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 proposed solution provides a high-strength seamless steel pipe with excellent sulfide stress corrosion cracking resistance, as evidenced by a high KILIMIT value, effectively addressing the limitations of existing technologies in sour environments.
Implementation Method 1
heating the steel pipe material to an austenite formation temperature of 1,200 to 1,300° C.
Implementation Method 2
the recuperation temperature Tr of the raw steel pipe at a pipe surface is (Ms+150° C.) or less, where Ms is a martensitic transformation start temperature
Implementation Method 3
a first hot rolling step of hot rolling the heated steel pipe material by piercing and elongating the steel pipe material with a rolling end temperature of 800° C. or more
Implementation Method 4
an intermediate cooling step of cooling a raw steel pipe after the first hot rolling step, the raw steel pipe being cooled from a cooling start temperature of 700° C. or more under the conditions that the average cooling rate is 40° C./s or more
Implementation Method 5
a direct quenching step of directly quenching the raw steel pipe continuously from the second hot rolling step, the raw steel pipe being quenched from a temperature equal to or greater than (Ar3+10° C.) under the conditions that the average cooling rate is 40° C./s or more
Implementation Method 6
a heat treatment step of subjecting the raw steel pipe after the direct quenching step to at least one run of a heat treatment that quenches the raw steel pipe after reheating to a temperature of 850 to 930° C., and subsequently tempers the raw steel pipe by heating to 650 to 730° C.
Data Source
AI summary
Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a yield strength of 758 MPa or more, and a KILIMIT value of 23.0 MPa√m or more as an evaluation index of sulfide stress corrosion cracking resistance.