Welded steel pipes with hot-dip or electro-galvanized layers on the surface. Galvanizing can increase the corrosion resistance of steel pipes and extend their service life. Galvanized pipes are widely used. In addition to being used as pipeline pipes for general low-pressure fluids such as water, gas, and oil, they are also used as oil well pipes and oil pipelines in the petroleum industry, especially offshore oil fields, and as oil heaters and condensation in chemical coking equipment. Pipes for coolers, coal distillate wash oil exchangers, pipes for trestle pipe piles, support frames for mine tunnels, etc.
Galvanizing methods for steel pipes: There are two categories: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing includes wet method, dry method, lead-zinc method, redox method, etc., and their processes are different.
The main difference between different hot-dip galvanizing methods is the method used to activate the surface of the pipe body to improve the galvanizing quality after acid leaching cleaning of the steel pipe. The dry method and redox method are mainly used in current production.
The surface of the zinc layer of electro-galvanizing is very smooth, dense, and uniform in structure; it has good mechanical properties and corrosion resistance; the zinc consumption is 60% to 75% lower than that of hot-dip galvanizing. Electro-galvanizing is technically complex, but this method must be used for single-sided coatings, double-sided coatings with different coating thicknesses on the inner and outer surfaces, and thin-walled pipe galvanizing.
Development of zinc layer materials
To meet the increasing requirements of various usage conditions and extend the service life of galvanized steel pipes, zinc layer materials are constantly developing. The main new coatings are:
(1) Iron-zinc alloy coating. That is, the steel pipe is heat-treated after galvanizing. For example, diffusion annealing at 500-550℃ for 10-15 minutes can extend the service life of galvanized pipes in oil fields by nearly 9 times;
(2) Galvanized layer containing multiple elements or trace alloy elements. For example, adding an appropriate amount of nickel can increase the corrosion resistance by more than 10 times compared with pure electroplated galvanized pipes;
(3) Composite coating. That is, according to the requirements of the use conditions, the galvanized layer of the steel pipe is coated with appropriate organic materials so that it can further meet one of the requirements in terms of corrosion resistance, high-temperature resistance, severe cold resistance, wear resistance, impact resistance, and increased elasticity. Several higher requirements. If colored coating is used, it also has decorative and logo effects.
Post time: Jan-17-2024