Stainless Steel Welded Pipe Acid Pickling Passivation

Austenitic stainless steel welded pipe has good corrosion resistance, high temperature oxidation resistance, good low temperature performance and excellent mechanical. It is widely used in chemical, petroleum, power, nuclear, aerospace, Marine, pharmaceutical, light industry, textile and other departments. It’s main application purpose is for corrosion resistance. The corrosion resistance of stainless steel relies mainly on the surface passivation membrane, if the film is incomplete or flawed, steel will corrode. acid pickling passivation treatment is the common way in real project, this way the corrosion potential of stainless steel is leveled up. In a stainless steel equipment and parts in the forming and assembling, welding, weld inspection, such as inspection, pressure test in the process of its construction and tag with surface oil, rust, dirt non-metallic, low melting point metal pollution, paint, welding slag and splash content etc, these substances affect the surface quality of stainless steel equipment and parts, destroyed the surface oxide film and reduce the general corrosion resistance and resistance to local corrosion of steel performance (including pitting, joint gap. Stainless steel welded pipe surface cleaning, acid pickling and passivation, in addition to the utmost to improve the corrosion resistance, it also has the effect of prevent product contamination and aesthetic. In "steel pressure vessel" regulation, "there is a requirement for anti-corrosion stainless steel and the surface of the container of the composite plate manufacture should be pickling passivation". This rule is made for petroleum chemical industry, pressure vessel, because the equipment is used for direct contact with the corrosive medium phase, starting from guarantee corrosion resistant corrosion resistance, acid pickling passivation is necessary. For other industrial sectors, such as not for anti-corrosion purpose, only based on the requirement of clean and good looking, there is no need for pickling passivation of stainless steel material. But pickling passivation is needed for the weld of the stainless steel equipment. Requirement is very strict when used in nuclear engineering, some chemical plant and others.
Stainless steel welded pipe corrosion ability is mainly relied a thin layer of the passivation film (about 1 nm) covered on the surface, 1 n the membrane corrosion dielectric isolation is the basic barrier of stainless steel protection. Passivation of stainless steel has the dynamic characteristic, it should not be defined as completely no corrosion process, it is a diffusion barrier layer, the anode reaction speed is reduced greatly. Usually in a reducing agent (such as chloride ions) keeps destroying the membrane, and exist in oxidizer (such as air) can maintain or repair the membrane.
Stainless steel welded pipes work pieces deposit in the air may form oxidation film, but this kind of membrane protective is imperfect. Standard process is to clean thoroughly, including alkaline cleaning and pickling, reoccupy oxidant passivation, to ensure the integrity and stability of the passive film. One of the purposes of pickling is to create favorable conditions for blunt treatment, guarantee the forming quality of passivation film. Because acid pickling can corrode 10 microns thick layer of surface of stainless steel, acid dissolving rate of defective parts of the chemical activity of higher than on the surface of the parts, so the pickling can make the entire surface evenly balanced, some original cause corrosion hidden trouble was removed. But more importantly, through pickling passivation, it is made of iron and iron oxide ratio of chromium and chromium oxide. To dissolve and remove the poor chromium layer, the surface enrichment of the chromium in stainless steel, the rich chromium passivation membrane potential can be up to + 1.0 V (SCE), close to the potential of precious metals, improve the stability of corrosion. Different passivation Richard will shadow.