Application of galvanized steel pipe

Product Application

Hot-dip galvanized steel pipes are widely used in manufacturing industries such as construction, machinery, coal mining, chemical industry, electric power, railway vehicles, automobile industry, highways, bridges, containers, sports facilities, agricultural machinery, petroleum machinery, prospecting machinery, and greenhouse construction.

Galvanized steel pipes are welded steel pipes with a hot-dip or electroplated zinc layer on the surface. Galvanizing can increase the corrosion resistance of steel pipes and extend their service life. Galvanized pipes have a wide range of uses. 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, oil heaters, condenser coolers, coal distillation and washing oil exchangers for chemical coking equipment, and pier pipe piles and support frames for mine tunnels.

Detailed Introduction

Hot-dip galvanized pipe

Hot-dip galvanized pipe is to make the molten metal react with the iron matrix to produce an alloy layer, so that the matrix and the coating are combined. Hot-dip galvanizing is to pickle the steel pipe first. In order to remove the iron oxide on the surface of the steel pipe, after pickling, it is cleaned in an ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride, and then sent to the hot-dip coating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life. The hot-dip galvanized steel pipe matrix undergoes complex physical and chemical reactions with the molten plating solution to form a corrosion-resistant and tightly structured zinc-iron alloy layer. The alloy layer is integrated with the pure zinc layer and the steel pipe matrix, so it has strong corrosion resistance.

Cold-dip galvanized pipe

Cold-dip galvanized pipe is electro-galvanized, with a small amount of galvanizing, only 10-50g/m2, and its corrosion resistance is much worse than that of hot-dip galvanized pipe. In order to ensure quality, most regular galvanized pipe manufacturers do not use electro-galvanizing (cold-dip galvanizing). Only small enterprises with small scale and outdated equipment use electro-galvanizing, and of course their prices are relatively cheaper. The Ministry of Construction has officially issued a document to eliminate cold-dip galvanized pipes with backward technology, and cold-dip galvanized pipes are not allowed to be used as water and gas pipes. The galvanized layer of cold-dip galvanized steel pipes is an electroplated layer, and the zinc layer and the steel pipe substrate are independently layered. The zinc layer is thin, and the zinc layer is simply attached to the steel pipe substrate and is easy to fall off. Therefore, its corrosion resistance is poor. In newly built houses, it is forbidden to use cold-dip galvanized steel pipes as water supply pipes.

Uses

Instructions

Galvanized pipes are often used. 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 large amount of rust will be generated in the pipes. The yellow water flowing out not only pollutes the sanitary ware, but also contains bacteria that grow on the rough inner wall. The rust causes excessive heavy metal content in the water, which seriously endangers human health.

Production steps

The process flow is: black pipe-alkali washing-water washing-acid washing-clean water rinsing-immersion aid-drying-hot dip galvanizing-external blowing-internal blowing-air cooling-water cooling-passivation-water rinsing-inspection-weighing-warehousing.

Technical requirements

1. Brand and chemical composition

The brand and chemical composition of steel used for galvanized steel pipes shall comply with the brand and chemical composition of steel used for black pipes specified in GB/T3091.

2. Manufacturing method

The manufacturing method (furnace welding or electric welding) of black pipes is selected by the manufacturer. Galvanizing adopts hot dip galvanizing method.

3. Threads and pipe joints

(a) For galvanized steel pipes delivered with threads, the threads shall be machined after galvanizing. The threads shall comply with the provisions of YB 822.

(b) Steel pipe joints shall comply with the provisions of YB 238; malleable cast iron pipe joints shall comply with the provisions of YB 230.

4. Mechanical properties The mechanical properties of steel pipes before galvanizing shall comply with the provisions of GB 3091.

5. Uniformity of galvanized layer Galvanized steel pipes shall be tested for uniformity of galvanized layer. The steel pipe specimen shall not turn red (copper color) after being immersed in copper sulfate solution for 5 consecutive times.

6. Cold bending test Galvanized steel pipes with a nominal diameter not exceeding 50mm shall be subjected to cold bending test. The bending angle is 90° and the bending radius is 8 times the outer diameter. No filler is used during the test, and the weld of the specimen shall be placed on the outside or upper part of the bending direction. After the test, there shall be no cracks or zinc layer peeling on the specimen.

7. Water pressure test The water pressure test should be carried out on the black pipe, and eddy current testing can also be used instead of water pressure test. The test pressure or eddy current testing comparison sample size should comply with the provisions of GB 3092. The mechanical properties of steel are important indicators to ensure the final performance (mechanical properties) of steel.

Rust removal method

1. First, use solvent to clean the steel surface to remove organic matter on the surface.

2. Then use tools to remove rust (wire brush) to remove loose or tilted scales, rust, welding slag, etc.

3. Use pickling.

Galvanizing is divided into hot-dip and cold-dip. Hot-dip is not easy to rust, while cold-dip is more likely to rust.