Cu-Zn Alloy Plated Steel Pipe Threaded Joint
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Solution Overview
Problem
Threaded joints for steel tubes in oil country tubular goods face challenges with galling resistance and corrosion, particularly when using green dope or solid lubricating coatings, which can lead to crevice corrosion and reduced leak and galling resistance.
Innovation Solution
A threaded joint with a Cu-Zn-M1 alloy plating layer, optionally accompanied by a Cu or Ni undercoating and a Sn-M2 alloy overlay, along with a lubricating coating, to enhance galling resistance and prevent crevice corrosion, while maintaining leak resistance without the need for heavy metal-containing greases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If green dope or solid lubricating coating is applied to improve galling resistance, then galling resistance is improved, but crevice corrosion occurs and corrosion resistance deteriorates
Solution Approach 1:
The patent divides the protective coating into multiple distinct layers: a base plating layer (Cu, Ni, or Zn) applied to the threaded joint surface, and a separate lubricating coating applied on top. This segmentation allows each layer to perform its specialized function - the base layer provides corrosion resistance while the top layer provides lubrication - thereby resolving the contradiction between galling resistance and corrosion resistance
Solution Approach 2:
The patent employs a composite coating structure combining different materials with complementary properties. The base plating layer uses metals with good corrosion resistance (Cu, Ni, Zn), while the lubricating coating uses materials with low friction coefficients. This composite approach enables simultaneous achievement of corrosion protection and galling resistance that single-material coatings cannot provide
2Adaptability or versatility
If repeated makeup and breakout operations are performed to enable periodic inspection, then adaptability is improved, but seal defects and galling occur due to strong friction
Solution Approach 1:
The patent applies a lubricating coating in advance on the threaded portions before any makeup operations begin. This preliminary lubrication layer is designed to withstand repeated friction during multiple makeup and breakout cycles, maintaining seal quality and preventing galling throughout the service life of the joint
Solution Approach 2:
The patent changes the surface friction parameter by applying a lubricating coating with low coefficient of friction on the threaded portions. This parameter change enables the joint to withstand repeated makeup and breakout operations without generating excessive friction that would cause seal defects or galling
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 excellent galling resistance and corrosion protection, allowing for repeated use without seal defects or galling, even in severe environments, and prevents crevice corrosion when green dope or lubricating coatings are applied.
Implementation Method 1
a threaded joint with a Cu-Zn-M1 alloy plating layer, optionally accompanied by a Cu or Ni undercoating and a Sn-M2 alloy overlay, along with a lubricating coating, to enhance galling resistance
Implementation Method 2
provides excellent galling resistance and corrosion protection, allowing for repeated use without seal defects or galling, even in severe environments, and prevents crevice corrosion when green dope or lubricating coatings are applied
Data Source
Figure 1~3
AI summary
A pin-box type threaded joint for steel tubes having a contact surface (30) including a threaded portion and a nonthreaded metal-to-metal contact portion has improved leak resistance, galling resistance, and corrosion resistance particularly to crevice corrosion. The contact surface of at least one of the pin and the box is coated with a first plating layer (34) made of a Cu-Zn alloy or a Cu-Zn-M1 alloy (wherein M1 is at least one element selected from Sn, Bi, and In). Optionally, an undercoat (32) of one or both of a Ni plating layer (32a) and a Cu plating layer (32b) and an overcoat of a Sn-M2 alloy plating layer (36) (wherein M2 is one or more elements selected from Bi, In, Ni, Zn, and Cu) may be formed below and above the first layer, respectively. A solid lubricating coating (38a) and a viscous liquid or semisolid lubricating coating (38b) may also be formed atop the plating layer as a lubricating coating (38).