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Causes of Small-diameter Seamless Steel Pipe Rust and How to Deal With It

Date:2019-07-11    keywords:seamless steel pipe,small diameter pipe,rust
Seamless steel pipes are widely used in our lives and are also suitable for all major factories, so the specifications and specifications are very high, especially the outer diameter of seamless steel pipes, which is small today. Let me introduce you to the factors that affect the accuracy of the outer diameter of seamless steel tubes.

1. Always slag. First, raise the temperature to the upper limit of the process temperature so that the zinc slag is separated from the zinc liquid, so that the zinc slag sinks to the bottom of the tank and is taken up by a zinc spoon or a special slag machine. The plated parts falling into the zinc liquid should be salvaged in time.
2. To prevent the iron in the plating agent from being brought into the zinc tank with the workpiece, the plating agent should be processed in the online regeneration cycle, and the ferrous content should be strictly controlled. It is not allowed to be higher than 4g/l, and the PH value is always maintained at 4.5-5.
3. Heating and heating should be uniform to prevent local overheating.

The hot-dip galvanized layer has a much better protective effect on steel than a paint or plastic layer. When hot-dip galvanizing, zinc and steel are diffused to form a zinc-iron intermetallic compound layer, that is, an alloy layer. The alloy layer is metallurgically bonded to steel and zinc, and is more firmly bonded than lacquer and steel. The hot-dip galvanized layer exposed to the atmosphere will not fall off for decades and will be completely corroded.

The outer diameter tolerance of seamless steel pipe depends on the sizing method, the operation and accuracy of the sizing equipment, and the sizing process system.

The sizing method is the primary factor in determining the outer diameter engineering. For longitudinally sizing and seamless steel pipes, the outer diameter accuracy can reach about 1%, while the cross-rolled sizing seamless steel pipe can achieve an outer diameter accuracy of 0.5%.

The influence of the process regime on the accuracy of the outer diameter depends mainly on the rolling temperature and temperature stability of the sizing machine. The rolling temperature is high, and the shrinkage of the seamless steel pipe after rolling is large, and the negative deviation from the outer diameter is likely to occur. On the contrary, the rolling temperature is low and may exceed the positive deviation, which may become a defective product and cause waste.

In addition, the manufacturer should continuously adjust the rolling mill according to the size specifications, steel grade, temperature condition and tool wear of the sizing seamless steel pipe to create favorable conditions for seamless steel pipe production, thus ensuring its outer diameter precision.

The geometrical accuracy of seamless steel tubes is determined by the tolerances of the outer diameter and wall thickness, while the inner diameter observation is generally not specified. Although the inner diameter accuracy is more important than the outer diameter accuracy in many cases, since there is no device with a fixed inner diameter in the production of hot rolled seamless steel tubes, there is no clear regulation on the inner diameter accuracy, however, In general, it can be assumed that the actual and relative accuracy of the inner diameter is a function of the outer diameter and wall thickness accuracy.

Add a small amount of calcium chloride (calcium chloride absorbs water vapor in the air to dry) in the first tube, and put a small-diameter seamless steel tube into the tube. A small-diameter seamless steel pipe was placed in the second test tube, and the small-diameter seamless steel pipe was immersed in the boiled and rapidly cooled distilled water, and the vegetable oil was injected to form an oil layer on the water surface. A small-diameter seamless steel pipe was placed in the third test tube, and a small amount of distilled water was added to immerse a part of the small-diameter seamless steel pipe in water. Three tubes were observed and recorded for a week. From the experimental results, we can find that the small-diameter seamless steel tubes in the first and second test tubes are not rusted, but the small-diameter seamless steel tubes in the third test tube are rusted, and the surface of the nails appears reddish brown. rust. It can be seen that the rust of small-diameter seamless steel pipes requires the participation of water and oxygen.

The corrosion process of steel products is a complex chemical reaction process. The rust is usually reddish brown, and different forms of rust are formed under different conditions. The rust is mainly composed of iron oxide hydrate (Fe2O3·nH2O) and iron hydroxide [Fe(OH)3]. The rust structure on the surface of the steel is loose, and it cannot prevent the internal iron from coming into contact with oxygen, water vapor, etc., and eventually the iron is completely rusted.

We understand the rusting conditions of small-diameter seamless steel pipes. It is only necessary to isolate steel products from water and oxygen to prevent steel corrosion. Therefore, the easiest way to prevent iron rust is to keep the surface of the steel product clean and dry. To prevent rusting of steel, a protective layer can also be formed on the surface, such as oiling, painting, firing enamel, spray molding, and the like. In daily life, people often paint paint on cars, buckets, etc., and the machine needs to apply mineral oil. In addition, a layer of metal that is not easily rusted, such as zinc, tin, chromium, nickel, etc., may be plated on the surface of the steel by electroplating or hot plating. These metal surfaces are capable of forming a dense oxide film that prevents iron products from rusting by contact with substances such as water and air. In addition, it is also possible to alloy steel to change the internal structure of the steel, for example, adding stainless steel to a metal such as chromium or nickel to form stainless steel, which effectively increases the rust resistance of the steel product.

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