Worldwide Pipe Meets Industry Standards
English Views: 10 Author: Site Editor Publish Time: 2024-12-23 Origin: Site
The manufacturing process of hot-dip seamless steel pipes includes acid pickling, washing with ammonium chloride or zinc chloride solutions, and finally hot-dip galvanizing. Here is a more detailed description of the process:
Purpose: Acid pickling is the first step in the manufacturing process, aimed at removing iron oxides, dirt, rust, and other impurities from the surface of the steel pipe. If these impurities are not removed, they can affect the quality of the subsequent galvanizing, causing uneven coating or even peeling.
Process:
The seamless steel pipe is first immersed in an acid pickling bath, usually using diluted sulfuric acid or hydrochloric acid solutions, which effectively dissolve the iron oxide on the surface of the pipe.
The temperature, acid concentration, and soaking time are controlled depending on the specific requirements of the pipe, typically around 30-60°C, with acid concentrations ranging from 5%-20%.
After the steel pipe is soaked for a certain period, most of the oxide layer and rust are removed, and the pipe surface becomes clean and shiny.
Purpose: After acid pickling, the steel pipe surface may still contain residues of the pickling acid. These residues must be completely washed away to prevent them from affecting subsequent processing.
Process:
The steel pipe is first rinsed with clean water to remove any pickling acid. This is typically done using a series of water washing tanks to ensure complete removal of the acid solution.
After washing, the pipe is rinsed again with clean water to ensure no acid remains, as any residual acid can cause corrosion.
Purpose: This step is aimed at further cleaning the surface of the steel pipe and preparing it for the next step of hot-dip galvanizing. The chloride solution helps remove any remaining moisture, acid, or other impurities while ensuring a high-quality surface for the upcoming galvanizing process.
Process:
The steel pipe is immersed in or sprayed with a solution of ammonium chloride (NH₄Cl) or zinc chloride (ZnCl₂), or a mixture of both. This step ensures that any residual moisture or acid is removed, preventing the formation of bubbles or uneven coating during the hot-dip galvanizing process.
The ammonium chloride solution prevents reactions between the zinc bath and the oxide or other impurities on the pipe surface, while the zinc chloride solution promotes better penetration and adhesion of the zinc.
The concentration, temperature, and soaking time of the chloride solution are also controlled. Typically, ammonium chloride concentrations range from 10%-20%, and zinc chloride concentrations are between 30%-40%. The immersion time generally ranges from several minutes to more than ten minutes, depending on the pipe's specific requirements.
Purpose: The hot-dip galvanizing process is the core step to provide the steel pipe with a protective zinc layer. This zinc layer not only enhances the pipe's corrosion resistance but also extends its service life, particularly for pipes exposed to harsh environments such as moisture and salt.
Process:
After acid pickling and chloride treatment, the seamless steel pipe is ready for hot-dip galvanizing in a bath of molten zinc.
The molten zinc bath is typically heated to temperatures between 450°C and 480°C. The steel pipe is immersed in the bath for a certain period, during which the surface forms a uniformly thick zinc layer.
During the hot-dip process, the zinc reacts with the steel surface to form a zinc-iron alloy layer, followed by a pure zinc layer. The zinc-iron alloy layer is crucial for corrosion resistance and helps protect the pipe from external corrosion.
The immersion time is critical. Too short an immersion time will result in a thin zinc layer, while too long will result in an excessively thick or uneven zinc layer. Immersion times typically range from a few seconds to several minutes, depending on the pipe size, shape, and required zinc layer thickness.
Purpose: After hot-dip galvanizing, the steel pipe needs to cool and solidify to ensure the zinc layer adheres firmly to the surface.
Process:
The steel pipe is removed from the zinc bath and enters the cooling section, where it is typically cooled using air or water.
As it cools, the zinc layer hardens and forms a stable outer layer. The cooling rate and method are adjusted according to the pipe's specifications and the required thickness of the zinc layer.
If the zinc layer is too thin or uneven, it can lead to peeling or localized corrosion of the steel pipe.
By combining acid pickling, chloride treatment, and hot-dip galvanizing, the hot-dip seamless steel pipe acquires excellent corrosion resistance and a long service life. This makes it widely used in various engineering projects, especially in pipeline systems for industries like petroleum, chemical engineering, and construction.
