Langfang New Powder Coating Co., Ltd.
Summary: There are many related standards for the application of epoxy powder coatings on pipelines, both domestically and internationally. This article provides a comprehensive comparison and explanation of standards from ISO, Canada, and China, to facilitate understanding and application of these standards by industry professionals.
- Pipeline transportation and railway, road, waterway, and air transportation are the five main modes of transportation currently. Compared to other transportation methods, pipeline transportation offers advantages such as low cost, high efficiency, short construction period, safety, and environmental friendliness, as well as the ability to traverse various areas. With the development of modern industry, pipelines have become an ideal transportation tool, offering a cost-effective, safe, and efficient transportation solution. Pipeline installation requires traversing complex terrains, and the pipeline environment is constantly changing, with corrosive gases and water present in the transported medium. Corrosion has always been a major challenge in pipeline transportation. Currently, common measures include cathodic protection and coating protection.
Currently, epoxy powder coatings play a crucial role in protecting pipelines, whether used as a single-layer epoxy coating, a multi-layer epoxy coating (such as double or triple layers), or in combination with three layers of polyethylene or polypropylene anti-corrosion coatings.
How can epoxy powder coatings better meet the requirements for pipeline corrosion protection? This document summarizes relevant domestic and international standards to facilitate understanding and application.
Among the standards summarized above, the Canadian standard has a significant influence, and many other standards reference and cite it. This standard was first published in 1992 and has undergone updates in 1998, 2002, 2006, and 2010. With each update, the standard's content has been enriched, and some indicators for epoxy powder coatings have also been adjusted. The ISO standard is a newer standard, but it is expected to eventually replace the Canadian standard and become the most influential international standard, which will be adopted by the domestic and international pipeline corrosion protection industry.
We will compare the relevant indicators specified in these standards regarding epoxy powder coatings, to identify the differences and commonalities in the requirements for epoxy powder coatings outlined in these standards.
Requirements for epoxy powder coating powder
1、Particle size distribution
In the table above, 150μm sieve corresponds to 100 mesh, and 250μm sieve corresponds to 60 mesh. These standards for epoxy powder are based on the concept of "fusion," so generally, pipes must be preheated. If it is purely electrostatic spraying, this particle size may seem too coarse. Regarding particle size distribution, it only specifies that ≤3.0 powder should be on the 150μm sieve and ≤0.2 powder should be on the 250μm sieve. For modern epoxy powder technology, these requirements are clearly too simple. For epoxy powder coatings, controlling and managing particle size is very important. The particle size of epoxy powder has a significant impact on the flowability of the powder, the electrostatic properties of the powder, the powder loading rate, the porosity of the powder coating, and the construction performance of the powder. Now, laser particle size analyzers are typically used to control particle size. This allows for control of both the average particle size and the amount of coarse and fine particles. The average particle size can be controlled between 45~55μm, and the amount of coarse particles can be controlled using the values specified in the standard.<15μm）的量应控制在10%以下，因为超细粒子一般易于漂浮，带电差，基于此原因在喷涂时超细粒子很难被吸附于管道上，从而被集尘装置抽走而到达布袋除尘器或滤芯除尘器，这些粒子已没有再利用的价值，而被防腐厂家做为垃圾倒掉。
2、Volatile Content
Due to the similar detection methods used in these standards for volatile content, the control limits are generally set at ≤0.6%. This indicates that excessive volatile content significantly impacts the density of epoxy powder coatings. The Canadian standard recommends using a titration method to measure volatile content, with a limit of ≤0.5%. This must be carefully controlled throughout the powder coating production and storage stages. This includes monitoring the water content of raw materials, the humidity of the production environment, and the hygroscopic properties of epoxy powder raw materials. Proper sealing during storage is also essential to effectively control volatile content.
3、Density
Foreign standards are typically determined by the manufacturers of powder coatings and should not exceed the specified range. Domestic standards are set at 1.3～1.5g/cm.3The density of epoxy powder is significantly affected by the color filler in the epoxy powder, which means the epoxy powder's resin content. In fact, for epoxy powder, its performance indicators are not necessarily lower density, which is why a specific density range has been designated in China. This is to prevent individual epoxy powder manufacturers from producing substandard products, which could affect product quality. Since other performance indicators can be controlled, there is no need to rely solely on density as a control measure.
4、Curing time
The curing time is related to the formulation of the epoxy powder, directly affecting the chemical crosslinking speed of the epoxy powder. For epoxy powders, neither too fast nor too slow curing is desirable. Fast curing can affect the wetting of the epoxy powder on the steel pipe substrate during melting, which in turn affects properties such as adhesion and corrosion resistance. Slow curing can affect the efficiency of applying the epoxy powder to the steel pipe. Therefore, curing time is a critical parameter that corrosion protection plants closely monitor. Generally, the curing time is jointly determined by the epoxy powder manufacturer and the pipe coating manufacturer. Domestic standards require ≥12 seconds. When using 3PE or 3PP anti-corrosion layers, the curing time of the epoxy powder must be determined, taking into account the production process of the anti-corrosion plant. It is essential to ensure that the epoxy powder coating does not fully cure before the epoxy powder is applied to the steel pipe and before the adhesive is squeezed and wrapped. Otherwise, it will affect the overall peeling strength of the coating.
5、Curing time
The speed of curing directly affects the production efficiency of pipe coating manufacturers. This is typically determined through negotiation between epoxy powder manufacturers and pipe coating manufacturers. Proper curing conditions are crucial for achieving the desired performance characteristics of the epoxy powder coating. Generally, epoxy powder manufacturers provide a curing curve to pipe coating manufacturers to facilitate adjustments to their production processes.
6、Thermal Properties
Thermal properties include the heat release of epoxy powder, the Tg1 and Tg2 values of epoxy powder coatings, and the Tg3 and Tg4 values of epoxy powder coatings. The heat release indicates the cross-linking density of the coating, while Tg1 reflects the storage stability of the epoxy powder, and Tg2, Tg3, and Tg4 reflect the heat resistance of the epoxy powder coating. Additionally, the degree of curing of the epoxy powder coating can be measured by comparing the heat release of the coating with the heat release of the powder, or by calculating the difference between Tg4 and Tg3.
Requirements for epoxy powder coating coatings
7、Adhesion
The typical testing periods for adhesion are 24h, 48h, and 28d. Short-term adhesion testing is used to quickly assess the adhesion of coatings and epoxy powder, while 28d testing is used as a type test to control and differentiate the quality of epoxy powder coatings and epoxy powder materials. The water temperature is determined based on the operating temperature of the pipeline. Obviously, higher temperatures and longer durations require higher quality for epoxy powder coatings.
8、Cathodic Disbondment
"The ability to resist cathodic delamination is a crucial indicator for epoxy powder coatings. This is because cathodic protection is an essential measure for preventing corrosion of pipelines. However, due to the effect of cathodic current, electrochemical reactions occur at defects in the coating, which can lead to a decrease in adhesion and detachment of the epoxy powder coating. To overcome this, stringent requirements for the cathodic delamination resistance of epoxy powder coatings are essential. The extent of cathodic delamination increases with increasing temperature, increased applied voltage, and longer duration."
9、Bending resistance
After applying epoxy powder coating to steel pipes, they will undergo lifting and transportation. These pipes may also be subjected to bending and forming, which inevitably causes deformation. Assessing the bending resistance of epoxy powder coatings is crucial to prevent damage during these processes. Due to variations in the location and environmental conditions of pipe installation, as well as different temperature requirements, standards specify measurements at 0°C, -18°C, and -30°C. In epoxy powder coatings, a balance between bending resistance, adhesion, and impact resistance is essential. Therefore, if the required standards are met, excessive bending resistance is not a concern.
10、Impact Resistance
Due to the inevitable collisions that occur during storage, transportation, and installation after coating application on pipes, it is crucial for epoxy powder coatings to exhibit good impact resistance under such external forces, preventing damage. This impact resistance is highly dependent on environmental temperature, typically decreasing as the temperature drops. Therefore, standards specify testing under extreme conditions, such as -30℃.
In addition to the indicators listed above, other relevant parameters include the porosity, water absorption rate, corrosion resistance, abrasion resistance, electrical strength, and volume resistivity of the coating. Due to space constraints, a complete list is not provided here.
Considering the domestic and international standards for epoxy powder coatings used in pipeline corrosion protection, the standards are continuously updated and incorporate new products and technologies in epoxy powder coatings. The requirements for epoxy powder coatings are becoming increasingly strict and comprehensive. Initially, only short-term indicators such as adhesion and electrochemical corrosion were controlled and tested. However, there is a growing emphasis on long-term testing to enhance the corrosion resistance and extend the service life of pipeline corrosion coatings. This requires epoxy powder coating manufacturers to continuously research and develop new technologies and conduct large-scale testing to produce high-quality products that meet the evolving requirements of the pipeline corrosion industry.