Brief introduction of national standard for hot dip galvanized pipe

Hot dip galvanized pipe-A layer of zinc is coated on the surface of the steel pipe, so that the steel pipe has strong corrosion resistance while maintaining the original steel properties. At present, hot-dip galvanized pipes are widely used in all walks of life, especially in the transportation projects of natural gas, gas and heating. But one thing to say is that since 2000, hot-dip galvanized pipes have been banned from being used for the transportation of domestic water.

So, what are the requirements for hot-dip galvanized pipes in major industries? Or what is the standard of hot dip galvanized pipe? The following small series will introduce you.

1. Hot-dip galvanized pipes have requirements for steel pipes used. According to national regulations, the raw materials of hot-dip galvanized pipes must conform to the brand and chemical composition of black pipes specified in GB3092. At the same time, the tensile strength, yield effect, elongation and shrinkage of the black pipe must meet the national requirements. No matter which mechanical properties are unqualified, it can be determined that this black pipe is unqualified, that is to say, this black pipe cannot be used for hot dip galvanized pipe.

Secondly, it is up to the steel pipe manufacturer to choose furnace welding or electric welding for the black pipe used for hot dip galvanizing, but the hot dip galvanizing method must be adopted for the black pipe.

Thirdly, the national standard stipulates that the thickness of galvanized layer must be uniform. The method to judge whether the thickness of galvanized layer is uniform is to soak the galvanized steel pipe sample in copper sulfate solution, and the continuous soaking times must be more than 5 times. Galvanized steel pipe does not change red, indicating that the galvanized layer is qualified; If it is found that the galvanized steel pipe turns red, it means that the thickness of galvanized layer is uneven or the galvanized quality is unqualified.

Fourthly, there are requirements for the surface quality of galvanized steel pipes in industry standards. The surface of galvanized steel pipe is smooth. Galvanized pipes with a small amount of roughness or zinc nodules on the surface can be judged as qualified; However, if there are black spots or bubbles on the surface of galvanized pipe, it can be directly judged that galvanized pipe is unqualified.

The above four standard requirements are the most important standard requirements for hot-dip galvanized pipes, and only steel pipes that fully meet the standards can be used for hot-dip galvanized pipes.

Classification characteristics:

Galvanized steel pipes are divided into cold compress pipes and hot compress pipes. The former has been banned, while the latter is advocated by the state.

hot-dip galvanizing

Hot dip galvanized pipe is an alloy layer formed by the reaction between molten metal and iron matrix, which combines the matrix with the coating. Hot dip galvanizing is to pickle the steel pipe first. In order to remove iron oxide from the surface of steel pipe, it is washed in the tank of ammonium chloride or zinc chloride aqueous solution or mixed aqueous solution of ammonium chloride and zinc chloride after pickling, and then sent to the hot dip plating tank. Hot dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. Complex physical and chemical reactions occur between the steel tube matrix and the molten plating solution, forming a zinc-iron alloy layer with dense structure and corrosion resistance. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix. Therefore, it has strong corrosion resistance.

1. Uniformity of galvanized coating: After the steel pipe sample is soaked in copper sulfate solution for 5 times continuously, it will not strain red (copper plating color).

2. Surface quality: The galvanized steel pipe surface should have a complete galvanized layer, and there should be no unpainted black spots and bubbles, and small rough surfaces and local zinc nodules are allowed.

3. Weight of galvanized layer: According to the requirements of the buyer, the weight of galvanized steel pipe can be used to measure the zinc layer, and the average value should be not less than 500g/ m2, and any sample should be not less than 480g/ m2.

Cold galvanized pipe

Cold galvanizing is electro-galvanizing, and the amount of galvanizing is very small, only 10-50g/m2, and the corrosion resistance is much worse than that of hot galvanized pipes. In order to ensure the quality, most regular galvanized pipe manufacturers do not use electro-zinc plating (cold plating). Only those small enterprises with small scale and outdated equipment adopt electro-zinc plating, and of course the price is relatively cheaper. At present, the Ministry of Construction has officially eliminated cold galvanized pipes with backward technology, and it is not allowed to use cold galvanized pipes as water and gas pipes in the future. The zinc layer is electroplated and separated from the steel pipe matrix independently. The zinc layer is thin, simply attached to the steel pipe matrix, and easy to fall off. Therefore, its corrosion resistance is poor. It is forbidden to use cold galvanized steel pipes as water supply pipes in new houses.

Use:

Now the iron pipes for gas, greenhouses and heating are also galvanized pipes. Like water pipes, galvanized pipes will produce a lot of rust and scale. The yellow water not only pollutes the sanitary ware, but also is mixed with bacteria that breed on the unsmooth inner wall. Due to corrosion, the content of heavy metals in water is too high, which seriously harms human health. In 1960s and 1970s, developed countries began to develop new pipes and gradually banned galvanized pipes. China Ministry of Construction and other four ministries and commissions also issued a document explicitly prohibiting galvanized pipes from 2000. At present, galvanized pipes are rarely used for cold water pipes in newly-built residential areas, and galvanized pipes are used for hot water pipes in some residential areas.

Finally, there is a requirement in the national steel industry that black pipes must be strictly inspected before hot dip galvanizing. After galvanizing, the galvanized pipe must also be inspected and trimmed. It can be said that the quality and quality of the hot-dip galvanized pipes currently on the market are completely reliable as long as they are produced by regular manufacturers, and friends can buy and use them with confidence.

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