What is the Purpose of Pickling Seamless Steel Pipes?

Passivation and Pickling seamless steel pipes is a chemical reaction. First, the oxide scale and rust on the steel surface can be removed through the pickling solution, and the passivation process is completed at the same time. It can effectively prevent the oxidation of seamless steel pipes and achieve the purpose of anti-corrosion.

Before pickling and passivating seamless steel pipes, oil, degreasing, and surface drawing compounds and other impurities must be removed. The surface of the seamless steel pipe after pickling and passivation turns into a uniform silvery white color, which greatly improves the corrosion resistance of stainless steel.

Seamless steel pipe phosphating is the seamless steel pipe immersed in phosphating liquid (some acid phosphate-based solution), deposited on the surface to form a layer of water-insoluble crystalline phosphate conversion film process, phosphating is a chemical and electrochemical reaction to form a phosphate chemical conversion film process, the phosphate conversion film is called phosphating film, so as to prevent metal corrosion to a certain extent.

It is used as a primer before painting to improve the adhesion and anti-corrosion ability of the paint film layer; it is used for friction reduction and lubrication in metal cold working processes.

The “phosphating and saponification” of seamless steel pipes refers to a process of re-saponification after phosphating. It is generally used in machining processes such as drawing or stretching. After the phosphating film is generally 8-12 microns, it enters the saponification solution and is then pulled or stretched.

The purpose of saponification of seamless steel pipes is to further increase the lubrication performance.

The brief process of pickling, phosphating and saponifying seamless steel pipe operating procedures: pickling → high pressure washing → phosphating → high pressure water washing → saponification → drying → transportation and stacking.

The process flow of pickling passivation seamless steel pipe

Seamless steel pipe pickling Passivation Seamless steel pipe secondary cold drawing is the raw material (capillary or finished pipe)→ head → pickling → phosphorus saponification (that is, lubrication)→ cold drawing, if there is a second cold drawing, do not need to annealing depends on what kind of steel.

Generally, low carbon steel does not need to be annealed. After cold drawing → lubrication → cold drawing → annealing → straightening → cutting → finished product inspection → packaging and storage. Those with high quality requirements should undergo pickling and passivation treatment.

Seamless pipe pickling passivation process In order to ensure the quality of pickling passivation, pickling passivation first need to consider the method of pickling passivation solution soaking, in the case that it is not convenient to use liquid soaking, to consider the method of brushing pickling passivation paste, but it is not appropriate to use the method of brushing pickling passivation solution. When the method of soaking with pickling passivation solution is used, the customary process of pickling passivation and testing of steel pipes is as follows :→ pickling → washing → Passivation (pool wash)→ pre-treatment → Pickling passivation (two-in-one) liquid (pool wash)→ scouring → Post-treatment → Pickling passivation (two-in-one) paste (pool wash)→ pre-treatment to remove the splash, solder, solder, dust and others on the surface of the weld and base metal.

The role of pickling passivating seamless steel pipes

In the process of prefabrication, welding, testing and heat treatment, the surface of the pipe (carbon copper pipe, stainless steel pipe) will accumulate iron oxide, welding slag, grease and other dirt, so that the corrosion resistance of the pipe changes.

After cleaning the pipe with acid washing liquid, the dirt on the surface of the pipe can be removed. After passivation treatment, a layer of anti-oxidation protective film can be formed on the surface of the steel pipe, so that the corrosion resistance of the steel pipe can be improved to ensure the normal operation of the production process.

Attention points when pickling and passivating seamless steel pipes

(1) Seamless steel pipe can not be pickled with a more corrosive formula, otherwise local corrosion will occur. But austenitic stainless steel can be pickled using the same process as pickling body stainless steel.

(2) The formula containing chloride ions has a faster pickling speed and is only used for the initial pickling of thick oxide film. After the initial pickling, the second pickling process is carried out with other pickling processes. Chlorine ions can easily cause spot corrosion of stainless steel. When preparing pickling solution, try to use distilled water to prevent the mixing of chloride ions.

(3) When scrubbing, rolling, or pickling with pickling paste, the pickling surface should always be kept moist and cannot be dried. Otherwise, the local acid concentration will be too high, which will produce cloudy patterns.

(4) In various pickling processes, attention must be paid to strictly controlling pickling temperature, time and other process conditions, otherwise there will be insufficient pickling, over pickling, and even workpiece corrosion and scrapping.

Why do ordinary seamless steel pipes need to be pickled?

For hot-rolled pipe materials or in-process pipes after intermediate heat treatment, the iron oxide scale on the inner and outer surfaces should be removed before cold processing of ordinary seamless pipes. The existence of iron oxide scale, on the one hand, affects the quality of subsequent lubrication; on the other hand, because its hardness is higher than the base metal, it will be pressed into the surface of the seamless steel pipe during cold working, causing defects. The result is: friction increases during processing deformation, tool wear intensifies, and the surface quality of the seamless steel pipe decreases, making the cold working process unable to proceed normally and effectively.

Therefore, it is very important to remove the tube material and the oxidized iron sheet on the surface of the product. In the cold processing production of seamless steel pipes, the removal of iron oxide sheet is widely used by chemical methods, that is, pickling method is generally used for carbon steel seamless pipes and low alloy seamless steel pipes, and pickling or alkali acid composite washing method is used for high alloy seamless steel pipes.

The production and process of seamless steel pipe is more, but also more complex, for the production of seamless steel pipe to use pickling and passivation, the purpose of doing so to increase the seamless steel pipe a layer of protective film, making the seamless steel pipe more strong and durable, so as to make the advantages more prominent.