Acid-Grafted Polyethylene Topcoat for Steel Pipe Joints
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Solution Overview
Problem
Existing methods for coating field-welded joints of polymer-coated steel pipes are complex and lack effective solutions for providing durable, corrosion-resistant coatings at construction sites, often requiring multiple layers and time-consuming processes.
Innovation Solution
A method involving a curable polymer coating followed by a topcoat layer comprising a non-elastomeric polyethylene and an elastomer, both grafted with an acid grafting agent, applied directly to the welded pipe segments without intermediate layers, offering strong adhesion and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-layer field joint coating structure (adhesive blend composition + polyethylene outer layer + through-cured epoxy layer) is used, then good mechanical and corrosion protection is achieved, but the coating process becomes too complicated for construction site application
Solution Approach 1:
The patent combines the adhesive blend composition and polyethylene outer layer into a single polymer composition layer applied over the epoxy coating. This merging of two separate layers into one integrated layer simplifies the coating structure while maintaining the protective functions of both the adhesive and polyethylene components.
Solution Approach 2:
The patent extracts and eliminates the intermediate adhesive blend composition layer from the complex three-layer field joint coating structure. By removing this intermediate layer and integrating its function into the polymer composition, the coating process becomes simpler and more suitable for construction site application.
2Strength
If multiple intermediate layers are used to achieve strong adhesion between the topcoat and factory coating, then bonding strength is improved, but the application process becomes time-consuming and complex
Solution Approach 1:
The patent applies the polymer composition to the epoxy coating while the epoxy is still in its reactive state, before complete curing occurs. This preliminary action allows the polymer composition to bond directly to the epoxy without requiring intermediate adhesive layers, reducing both complexity and application time while maintaining strong adhesion.
3Ease of manufacture
If a simplified two-layer coating structure is used, then the application process is streamlined, but adhesion strength and mechanical properties may be compromised
Solution Approach 1:
The patent uses a composite polymer composition consisting of polyethylene and elastomer components in specific proportions (60-85 wt% polyethylene, 15-40 wt% elastomer). This composite material provides both the simplicity of a two-layer structure and the mechanical strength required for durable coating adhesion.
Solution Approach 2:
The patent optimizes the molecular weight distribution and composition ratios of the polymer components to achieve the desired balance between application simplicity and mechanical performance. By controlling parameters such as polyethylene molecular weight (10,000-500,000) and elastomer content, the coating achieves adequate peel strength while maintaining process simplicity.
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 method provides a straightforward, durable coating with excellent peel strength, environmental stress crack resistance, and Shore D hardness, meeting the requirements of Class A three-layer polyolefin coatings, while simplifying the application process and enhancing protection against corrosion and mechanical damage.
Implementation Method 1
an first coating layer comprising a curable polymer and a topcoat layer comprising an acid-grafted polymer composition comprising a non-elastomeric polyethylene and an elastomer
Data Source
AI summary
The present invention relates to a method of joining polymer coated steel pipes comprising the steps of—providing polymer coated pipe segments with an uncoated length on both ends of the segments; —welding the polymer coated pipe segments together; —applying a curable polymer (A) onto the uncoated length of the welded pipe segments to form an first coating layer; and—applying a polymer composition (B) onto the first coating layer to form a topcoat layer with a thickness of 0.5 to 10 mm, wherein the polymer composition (B) has a melt flow rate MFR2 of 1.0 to 6.0 g/10 min, determined according to ISO 1133 at a temperature of 190° C. under a load of 2.16 kg, and includes a base resin comprising (B-1) a non-elastomeric polyethylene in an amount of 60 to 85 wt % of the total polymer composition being produced in a process using a single-site catalyst, and (B-2) an elastomer comprising a copolymer of ethylene and at least one polar comonomer, wherein component (B-1) or components (B-1) and (B-2) have been grafted with an acid grafting agent and the use of polymer composition (B) as topcoat layer with a thickness of 0.5 to 10 mm in a coating of coated steel pipe field-joints, a method of coating a steel pipe and the use of polymer composition (B) for the coating of steel pipe joints or steel pipes.