Zn-Ni Plated Oil-Well Steel Pipe for Galling-Resistant Threads
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Solution Overview
Problem
Large-sized oil-well steel pipes experience increased galling due to longer sliding distances during fastening and loosening, leading to reduced galling resistance, even with Zn--Ni alloy plating layers, as the existing chemical composition and plating layer thickness do not adequately prevent peeling and subsequent friction increases.
Innovation Solution
An oil-well steel pipe with a chemical composition of C: 0.01 to 0.60%, Cr: 0 to 8.0%, and Fe: 80.0% or more, featuring a Zn--Ni alloy plating layer with a C-concentrated layer thickness within 0 to 1.50 μm, which enhances the galling resistance by preventing peeling and maintaining friction durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pipe size is increased, then the oil well production capacity is improved, but the sliding distance during fastening increases leading to easier galling occurrence
Solution Approach 1:
The patent applies a Zn-Ni alloy plating layer specifically on the pin contact surface and box contact surface of large-sized oil-well steel pipes. This local treatment concentrates the protective function where friction occurs most intensely, providing enhanced galling resistance exactly where needed without requiring treatment of the entire pipe structure.
Solution Approach 2:
The patent specifies precise compositional parameters for the Zn-Ni alloy plating layer (Zn: 60-80 mass%, Ni: 20-40 mass%) and controls the plating layer thickness within 5-25 μm. By optimizing these parameters, the plating layer achieves the right balance of hardness, adhesion, and friction properties to prevent galling in large-diameter pipes with long sliding distances.
2Reliability
If a compound grease is applied to improve galling resistance, then the friction durability is enhanced, but heavy metals in the grease pollute the environment
Solution Approach 1:
The patent removes harmful heavy metal compounds from the lubrication system by replacing compound grease with a Zn-Ni alloy plating layer. The plating layer provides the necessary friction reduction and galling resistance through its inherent material properties rather than through oily additives, thereby eliminating environmental pollution while maintaining protective function.
Solution Approach 2:
The Zn-Ni alloy plating layer serves as a durable, reusable protective coating that eliminates the need for repeated application of polluting compound greases. Once applied, the plating layer provides long-lasting galling resistance without the environmental drawbacks of organic lubricants containing heavy metals.
3Reliability
If a Zn-Ni alloy plating layer is formed to enhance galling resistance, then the wear resistance is improved, but the plating layer may peel off increasing friction
Solution Approach 1:
The patent precisely controls the plating layer thickness within 5-25 μm and optimizes the Zn-Ni alloy composition (Zn: 60-80 mass%, Ni: 20-40 mass%). These parameter optimizations ensure the plating layer is thick enough to provide wear resistance and galling protection, yet thin enough to maintain strong adhesion to the base steel, preventing peeling during repeated fastening and loosening operations.
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 specified chemical composition and Zn--Ni alloy plating layer thickness significantly improve galling resistance, allowing for repeated fastening and loosening cycles without galling, even in large-diameter pipes, by reducing the likelihood of peeling and maintaining interfacial stability.
Implementation Method 1
The Zn contained in the Zn—Ni alloy plating layer formed on a contact surface of the oil-well steel pipe enhances the corrosion resistance of the base material of the oil country tubular good by sacrificial protection
Implementation Method 2
The pin contact surface and the box contact surface repeatedly experience strong friction during fastening and loosening of the oil-well steel pipe
Data Source
AI summary
An oil-well steel pipe according to the present disclosure includes: a pipe main body that includes a pin which includes a pin contact surface, and a box which includes a box contact surface; and a Zn—Ni alloy plating layer which is formed on at least one of the pin contact surface and the box contact surface. The chemical composition of the pipe main body contains, in mass %, C:0.01 to 0.60%, Cr:0 to 8.0% and Fe:80.0% or more. In addition, when a region containing C in an amount that, in mass %, is 1.5 times or more greater than the C content of the pipe main body is defined as a C-concentrated layer, the thickness of the C-concentrated layer in the wall thickness direction of the pipe main body is within the range of 0 to 1.50 μm.