Multilayer Zn-Ni Thread Coating for Low-Torque Seizure Resistance
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Solution Overview
Problem
Existing coatings for tubular threaded elements in the oil and gas industry face challenges such as corrosion, dilapidation, and increased screwing torque, leading to risks of seizure and leakage.
Innovation Solution
A multilayer coating system comprising a first layer of electro-deposited zinc-nickel, a second layer of oxalation-type conversion, and a third layer of polyurethane or epoxy matrix with lubricating particles, which enhances lubrication, stability, and anti-corrosion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid deposit coating is applied to prevent corrosion and seizing, then anti-corrosion protection and lubrication are improved, but the coating is subject to corrosion and delamination in aggressive environments
Solution Approach 1:
The patent applies a composite coating system consisting of multiple layers: a zinc-nickel alloy layer combined with a polymeric topcoat containing lubricating particles. This composite structure allows the metallic layer to provide corrosion protection while the polymeric layer provides environmental stability and sustained lubrication, preventing delamination and corrosion of the underlying metal deposit.
Solution Approach 2:
The patent modifies the coating system by changing the chemical composition and physical properties of the coating layers. Specifically, it uses a zinc-nickel alloy with specific ratios (7-14% nickel) combined with a polymeric matrix containing solid lubricating particles, transforming the coating from a simple metallic deposit to a sophisticated multi-functional composite material with enhanced stability.
2Ease of operation
If grease is applied to reduce friction and prevent seizing, then lubrication is improved, but grease is extruded and released into the environment causing blockages
Solution Approach 1:
The patent replaces the extrudable grease with a solid lubricating system embedded in a polymeric matrix. The lubricating particles (such as PTFE, graphite, or MoS2) are distributed throughout the topcoat and provide sustained lubrication through solid-state mechanisms, eliminating the need for grease that would be extruded and cause environmental blockages.
Solution Approach 2:
The patent substitutes the mechanical lubrication system (grease film) with a solid-state lubrication system. The lubricating particles embedded in the polymeric topcoat provide low-friction surfaces through solid-state mechanisms, replacing the need for extrudable grease while maintaining effective lubrication during screwing operations.
3Strength
If high axial load is applied during screwing operations, then connection strength is improved, but the risk of seizure in threaded areas increases
Solution Approach 1:
The patent introduces a lubricating topcoat as an intermediary layer between the metallic coating and the contacting surfaces. This topcoat contains solid lubricating particles that reduce the coefficient of friction, allowing high axial loads to be applied during screwing operations without causing seizure, while still achieving strong mechanical connections.
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 coating system achieves a stable and durable friction coefficient less than 0.2, reducing the risk of seizure and improving screwing capacity, while also providing enhanced anti-corrosion protection and improved adhesion in wet conditions.
Implementation Method 1
a first layer comprising a solid coating comprising Zinc-Nickel electrodeposited on said at least a portion of the surface of the threaded end
Implementation Method 2
a second oxalation type conversion layer above the first layer
Implementation Method 3
a third layer comprising a polyurethane or epoxy matrix loaded with lubricating solid particles above the second layer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A threaded tubular element (1, 2) for use in drilling, operating hydrocarbon wells, transporting petroleum and gas, transporting or storing hydrogen, carbon capture or in the field of geothermal energy, comprising a metal body (5) and at least one threaded end (3, 4) comprising at least one threaded portion (14,15), the threaded end (3, 4) comprising a multilayer coating (10) on at least one portion of the surface of the threaded end (3, 4), characterised in that the multilayer coating (10) comprises a first layer (11) comprising a solid zinc-nickel coating electrodeposited onto the at least one portion of the surface of the threaded end (3, 4), a second oxalate conversion layer (12) above the first layer (11), a third layer (13) comprising a polyurethane matrix or an epoxy matrix filled with solid lubricating particles above the second layer (12).