Ductile Iron Pipe External Coating for Buried Corrosion
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Solution Overview
Problem
Ductile cast iron piping members buried in soil face unique corrosion challenges due to varying soil conditions, requiring effective corrosion protection that existing Zinc and Aluminium coatings alone cannot adequately address, especially in aggressive environments.
Innovation Solution
A method involving a first layer of thermally sprayed Zinc-Aluminium pseudo alloy coating combined with a second layer of modified Cashew Nut Shell Liquid (CNSL) resin-based paint, which provides enhanced corrosion resistance, toxicity-free, and low VOC properties, forming a hard and tough film for improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single layer of Zinc or Aluminium coating is applied, then the coating process is simple and cost-effective, but the corrosion resistance is insufficient in aggressive soil environments
Solution Approach 1:
The patent applies a composite coating structure consisting of a Zinc-Aluminium alloy layer (5-15% Aluminium by weight) combined with a bitumen-based paint layer. This composite structure leverages the cathodic protection properties of Zinc-Aluminium alloy while the bitumen layer provides additional barrier protection against aggressive soil environments, thereby enhancing overall corrosion resistance beyond what single-layer coatings can achieve.
Solution Approach 2:
The Zinc-Aluminium alloy coating serves multiple functions: it provides cathodic protection through sacrificial anode action, forms a protective barrier layer, and when combined with bitumen paint, creates a multi-functional coating system that addresses both electrochemical and physical corrosion mechanisms in diverse soil conditions.
2Reliability
If a thicker coating layer is applied to improve corrosion protection, then the corrosion resistance increases, but the material consumption and cost increase
Solution Approach 1:
The patent uses a composite coating system where a relatively thin Zinc-Aluminium alloy layer (providing cathodic protection) is combined with a bitumen paint layer. This composite approach achieves superior corrosion protection compared to thick single-layer coatings, as the two materials work synergistically to protect the substrate with optimized material consumption.
Solution Approach 2:
The patent optimizes the Aluminium content in the Zinc-Aluminium alloy to 5-15% by weight, which provides adequate corrosion resistance without excessive material consumption. This parameter optimization ensures effective protection while controlling coating thickness and material usage.
3Duration of action of stationary object
If standard Zinc-Aluminium coating is used, then the application process is straightforward, but the coating lacks sufficient adhesion and durability in aggressive environments
Solution Approach 1:
The patent combines Zinc-Aluminium alloy coating with bitumen-based paint to create a composite system where the bitumen layer enhances adhesion and durability. The bitumen acts as a binder that seals the porous structure of the metal coating, preventing corrosive agent penetration and improving overall coating longevity in aggressive environments.
Solution Approach 2:
The patent applies different materials with specific properties to different functional requirements: the Zinc-Aluminium alloy provides cathodic protection at the metal-coating interface, while the bitumen paint layer provides environmental barrier and adhesion enhancement at the coating-exposure interface, optimizing performance at each interface.
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 significantly increases the lifespan of ductile iron pipes by offering superior corrosion resistance, acid and alkali resistance, water repellence, and anti-microbial properties, while being economical and environmentally friendly, effectively protecting against corrosion in diverse soil and ambient conditions.
Implementation Method 1
The development of special sacrificial anodic coating to protect the substrate from corrosion is possible. A coating with an alloy of metallic Zinc and Aluminium performs excellently for corrosion resistance.
Implementation Method 2
ease in application coupled with optimum corrosion protection ability are the factors that restrict the use of Zinc or Aluminium individually. Although, Zinc is used individually for general corrosion protection, Aluminium is not used individually. The coating with an alloy of Zinc and Aluminium overcomes the above limitation
Data Source
Figure 1(a)~1(b)
AI summary
The present invention relates to improvement of the outside anticorrosive treatment of ductile cast iron piping members, through the development of a Pseudo Alloy metallic film along with modified paint on the external surface, more particularly the present disclosure relates to the improved corrosion resistant to ductile cast iron piping members, specially when used in buried condition, the coating method that can form an anticorrosion pseudo metal alloy layer in the peripheral surface along with a modified Cashew Nut Shell Liquid (CNSL) paint.