Corrosion protection coating for Water pipeline

2023,12,08

During the year-round operation of water supply pipelines, due to physical, chemical, electrochemical, and microbiological effects, rust scale gradually forms along the inner wall of the pipeline. As the pipeline age increases, the rust scale continuously thickens, resulting in a decrease in the water flow section. The water inside the pipeline flows along the rust scale, and the hygiene condition of the rust scale will directly affect the water quality of the water supply.

Since the existence of water supply projects around the world, people have been tirelessly exploring and researching the corrosion mechanism, anti-corrosion methods, coating structures, etc. of buried metal pipelines, and various anti-corrosion systems have been formed. The pipes used in the water supply network are generally divided into metal pipes and non-metal pipes. From the current pipeline network, large diameter pipes generally use metal pipes, including cast iron pipes, ductile iron pipes, and steel pipes. Small diameter pipes generally use non-metallic pipes, including nylon pipes and PPR pipes for water supply. However, some pipes and fittings are still connected by steel pipes or steel fittings. Due to the lower winter temperatures in the north, both trunk pipelines and urban pipeline networks are generally buried underground, which requires high anti-corrosion requirements for the pipeline network. Good anti-corrosion can avoid water leakage caused by pipeline corrosion, increase friction inside the pipeline, and pollute water quality. On the contrary, it can bring great trouble to the pipeline network, indicating how important pipeline anti-corrosion is for the pipeline network.

1. Corrosion of pipelines

Corrosion is a type of damage caused by the chemical and electrochemical reactions of metals in the surrounding medium. Metal corrosion can be divided into chemical corrosion and electrochemical corrosion according to their properties. Chemical corrosion is the process in which a metal directly comes into contact with a medium and undergoes chemical reactions, resulting in the dissolution of metal ions. Electrochemical corrosion is the electrolysis process that occurs in a primary battery composed of metals and electrolytes. Metals generally undergo electrochemical corrosion in electrolyte solutions such as soil, water, or moisture. The causes of external corrosion of buried pipelines are quite complex, generally summarized into the following three reasons:

1. Electrochemical corrosion - Due to the complex mixture of solid, liquid, and gaseous substances in soil, which has the characteristics of electrolyte solutions, the exposed metal in buried pipelines forms a primary battery with the soil electrolyte, leading to electrochemical corrosion of the metal.

2. Corrosion of pipelines by stray currents - due to external leakage, stray currents in the soil pass through the pipeline, resulting in electrolysis and causing pipeline corrosion.

3. Corrosion caused by bacterial action - According to research, the corrosion behavior of different types of bacteria varies under different conditions when microorganisms participate in the corrosion process.

Investigation and research on corrosion of buried pipelines have shown that damage to the insulation layer on the outer wall of buried pipelines is the main cause of soil corrosion. In order to ensure long-term safe production of pipelines, in response to the characteristics of soil corrosion, the following ways can be taken to prevent the occurrence of corrosion and reduce the degree of corrosion:

(1) Select corrosion-resistant pipes;

(2) Increase the transition resistance between the pipeline and the soil, reduce the corrosion current, and use insulation layers such as epoxy coal tar anti-corrosion coating, adhesive tape, epoxy powder, and three-layer PE to increase the resistance of the insulation layer and improve its density (without pinholes), thereby minimizing the corrosion current;

(3) Using electrical protection (cathodic protection and sacrificial anode protection), general electrical protection should be combined with insulation layer protection to reduce the consumption of protection current.

2. Corrosion prevention of pipelines

The outer wall is mostly coated with epoxy in China. In recent years, China has successively researched and developed anti-corrosion technologies such as polyethylene cold wound tape (two-layer structure), Visco Elastic Coating Materials/fusion bonded epoxy powder coating, Cold Applied Polymer Tape and Heat Shrinkable Sleeves, achieving good anti-corrosion effects. However, in practical applications, the shortcomings of these anti-corrosion technologies have also been exposed, such as poor adhesion of two-layer polyethylene jackets, low mechanical properties of fusion bonded epoxy powder layers, and difficulty in ensuring the construction quality of polyethylene adhesive tapes. Therefore, some European countries have developed and successfully applied heat shrink material technology since the 1980s, This is currently considered the most advanced external anti-corrosion technology for pipelines internationally. HDPE polyethylene coating is widely recognized as one of the most promising anti-corrosion materials due to its excellent physical and mechanical properties, good chemical corrosion resistance, extremely low water and oxygen permeability, and low environmental pollution. However, the poor adhesion between non-polar polyethylene coatings and polar steel pipe surfaces has not been effectively resolved yet.

The most commonly used inner walls are solvent-free epoxy anti-corrosion coatings and IPN interpenetrating network anti-corrosion coatings.

3. Anti corrosion process of pipelines

Pipeline coating: Coating the outer wall of buried metal pipelines can significantly improve their service life.

1. Rust removal process. The rust removal process is more convenient than other anti-corrosion processes. Simply use sandpaper, wire brush, or electric grinder to remove floating rust, welding slag, oil stains, and loose substances on the surface of the coated workpiece, and wipe it clean until it is flat and dry before applying. It should be emphasized that the surface of the coated workpiece must be cleaned of floating rust, oil stains, and other debris, otherwise it will affect the adhesion and coating quality of the coating.
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2. Coating process. Brushing, spraying, rolling and other methods can be used for coating. a. Ordinary anti-corrosion type (two bottoms and two sides). One primer → One primer → One topcoat → One topcoat. Dry film thickness approximately 200 μ M. Wet film thickness is about 250 μ M, Liquid Epoxy Coatings covered Epoxy Primer,High Temperature Epoxy Primer,Field-Applied Coatings Materials.

Author:

Ms. Tao

E-mail:

forever@caepforever.com

Phone/WhatsApp:

++86 19182078675