Pretreatment of stainless steel pipe fittings before pickling

After rolling of stainless steel pipe fittings, it’s surface of the scale and the collective combined with strong, difficult to remove, if directly for pickling, the effect is not very good, so can be a pretreatment measures first, and then the oxidant, activator of mix acid cleaning can be more effective to remove oxide skin stainless steel.

There are two kinds of pretreatment methods for stainless steel pipe fittings: alkali dip and shotblast.

1, alkali leaching

Base leaching is the structure of a tube that is immersed in an alkaline molten salt or solution which changes the oxide skin. Base leaching can be classified as molten salt alkali and solution alkali leaching. Stainless steel surface intact by the molten salt leaching, acid pickling metal loss is relatively small, and can greatly shorten the pickling time, improve the efficiency of production, the molten salt to keep in high temperature condition, high energy consumption, molten salt leaching of another disadvantage is the need for specialized alkali trough, alkali bath temperature cycle is long, large energy consumption. Some manufacturers are not able to produce in a continuous production, and the solution base immersion process is chosen. The principle of solution alkalinity is the same as that of molten salt, but the temperature is lower than the boiling point of the solution, and the corresponding length is correspondingly. In alkaline aqueous solution of potassium permanganate (temperature is about 100 ℃) soaked although save energy, but the production efficiency is low, only as a supplementary means.

2, shot peening method

Shot peening method is to use shot nine machines will pill grain accelerated to a certain speed, and spray at a certain Angle to the rotation of the surface of the pipe, under the impact of the pill grain, the surface of the steel to produce elastic deformation, scale almost no elastic deformation capacity, so the scale is broken and loose, fall off. General carbon steel and low alloy steel pipe scale thicker, the weaker with substrate with shot peening method of scale removal can be clean, but the stainless steel pipe scale thin, dense, adhesive strength with substrate, it is difficult to clear the scale by shot peening method is clean, can only as a pretreatment before pickling means much for annealing martensite steel, ferritic steel, and do not allow the alkali pretreatment of immersion precipitation hardening stainless steel pipe fittings. The pellet is chosen to have a certain hardness, the steel pellet that is resistant to fracture. The material, diameter, the speed of the shot and the amount of pills will affect the surface of the cleaned pipe. The shotblast method is divided into two kinds: single root expansion shot blasting and disc spray shot, and the production efficiency is considered, and the scale production is appropriate to choose the disc type.

The advantages of shotblasting method: high efficiency, energy saving, small occupation area, no pollution environment, suitable for mass production. The drawback is that it is a one-off investment.

Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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