Classification and process description of galvanized pipes

Classification of galvanized pipes: Galvanized steel pipes are divided into cold-plated pipes and hot-dip pipes.

1. Hot-dip galvanized pipe

     Hot-dip galvanizing makes the molten metal react with the iron matrix to produce an alloy layer, thereby combining the matrix and the coating. Hot-dip galvanizing first pickles the steel pipe. In order to remove the iron oxide on the surface of the steel pipe, after pickling, It is cleaned in an aqueous solution of ammonium chloride or zinc chloride or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to a hot-dip plating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life.  2. Cold galvanized pipe

     Cold galvanizing is electroplating. The amount of galvanizing is very small, only 10-50g/m2. Its corrosion resistance is much worse than that of hot-dip galvanized pipes. Most regular galvanized pipe manufacturers do not use electroplating in order to ensure quality. Zinc (cold plating). Only small businesses with small scale and old equipment use electro-galvanizing. Of course, their prices are relatively cheaper. At present, the Ministry of Construction has officially issued a notice to eliminate cold-dip galvanized pipes with backward technology. In the future, cold-dip galvanized pipes are not allowed to be used. Galvanized pipes are used as water and gas pipes.

3. Hot-dip gi steel pipe      The steel pipe matrix undergoes complex physical and chemical reactions with the molten plating solution to form a corrosion-resistant zinc-iron alloy layer with a tight structure. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, it has strong corrosion resistance.

4. Cold galvanized steel pipe

     The zinc layer is an electroplated layer, and the zinc layer is layered independently from the steel pipe base. The zinc layer is thin, and the zinc layer simply adheres to the steel pipe base and easily falls off. Therefore, its corrosion resistance is poor. In new residential buildings, the use of cold-dip galvanized steel pipes is prohibited. As a water supply pipe.

 Steel pipes must undergo pre-plating treatment before galvanizing:

     That is, pickling, cleaning, rinsing, dipping in solvent, and drying. The welded pipe is hoisted by a crane to the pickling tank for pickling (about 2 tons per hoist). Pickle with about 26% hydrochloric acid solution. In order to prevent excessive pickling and acid mist volatilization, add 0.5~1.0g/L corrosion inhibitor and fog suppressor to the pickling solution, and pickle at room temperature. The pickling time is generally The time is 30 to 60 minutes. In order to ensure that the steel pipe can be pickled evenly, a crane is used to lift the steel pipe 2 to 3 times during the pickling process to improve the pickling effect. When the acid concentration drops to 100g/L, it should be supplemented or replaced, and the iron content reaches 220~260g/L and is discharged as waste acid. The pickled steel pipes are hoisted by a crane to the cleaning tank for cleaning to remove the residual acid and iron salts accumulated on the surface of the steel pipes after pickling. Then they are hoisted to the washing bench and rinsed with 0.7~0.8Mpa water. After the water drips dry, The steel pipe is lifted into the solvent tank for dip coating. The dipping time is about one minute. The solvent uses 600~650g/L zinc chloride, 80~100g/L ammonium chloride and 1~2g/L OP-10 surfactant. In order to improve the pre-plating effect of the steel pipe in solvent, the solvent is always kept weakly alkaline, and then it is lifted from the crane to the drying furnace bench and entered into the drying furnace for drying. The drying temperature is 100~130 degrees and the time is generally 6~10 minutes.

     Optimization of sulfate galvanizing The biggest advantage of sulfate galvanized pipe is that the current efficiency is as high as 100% and the deposition rate is fast, which is unmatched by other galvanizing processes.

Optimization of sulfate galvanized pipes:

     Because the crystallization of the coating is not fine enough, the dispersion ability and deep plating ability are poor, so it is only suitable for plating pipes and wires with simple geometric shapes. The sulfate electroplating zinc-iron alloy process optimizes the traditional sulfate galvanizing process. Only the main salt zinc sulfate is retained, and the remaining components are discarded. An appropriate amount of iron salt is added to the new process formula to form a zinc-iron alloy coating from the original single metal coating.

     The reorganization of the process not only brings forward the advantages of high current efficiency and fast deposition rate of the original process, but also greatly improves the dispersion ability and deep plating ability. In the past, complex parts could not be plated, but now both simple and complex parts can be plated, and the protective performance is also 3 to 5 times higher than single metal. Production practice has proven that when used for continuous electroplating of wires and pipes, the coating grains are finer and brighter than the original ones, and the deposition rate is fast. The coating thickness reaches the requirement within 2 to 3 minutes.

Application range of galvanized pipes:

     Galvanized steel pipes are divided into two types: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing has a thick zinc layer and has the advantages of uniform coating, strong adhesion, and long service life. The cost of electroplated galvanizing is low, the surface is not very smooth, and its corrosion resistance is much worse than that of hot-dip galvanized pipes.

     In order to improve the corrosion resistance of steel pipes, general steel pipes are galvanized. Galvanized steel pipes are divided into two types: hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing has a thick zinc layer, while electro-galvanizing has low cost and the surface is not very smooth.

     Most of the old houses use galvanized pipes, and the iron pipes used for gas and heating are also galvanized pipes. Galvanized pipes are used as water pipes. After a few years of use, a lot of rust and scale are produced in the pipes, and the yellow water flowing out not only pollutes the Sanitary ware, and mixed with bacteria that breed on the rough inner wall, rust causes excessive heavy metal content in the water, seriously endangering human health.

     In the 1960s and 1970s, developed countries in the world began to develop new pipes and gradually banned galvanized pipes. China's Ministry of Construction and four other ministries and commissions have also issued documents clarifying that galvanized pipes will be banned from 2000. At present, galvanized pipes are rarely used in cold water pipes in newly built residential areas, and hot water pipes in some residential areas use galvanized pipes.