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Seamless Steel Pipe Pickling Passivation

Date:2019-05-30    keywords:seamless steel pipe, pickling, passivation

Seamless steel pipe pickling passivation process steps


Washing→degreasing to oil→washing→second oil removal→hot water washing→acid washing→water washing→neutralization→water washing→chromic anhydride immersion second time ash→water washing→passivation→hot water washing→drying→checking→sealing → Brush primer → custody


Operation process


Washing: rinsing the inner and outer sludge of the pipe with a normal temperature water of not less than 0.5 MPa, degreasing and degreasing; 
Heating with 3% caustic soda solution to 80°C for 2h → water washing; 
Using normal temperature water with a pressure not lower than 0.5 MPa Rinse → second degreasing and de-oiling; 
Use trisodium phosphate, sodium carbonate, water glass, petroic acid 6% to 70°C~90°C for 30 min → hot water wash; 
Soak with warm water at 50°C ~ 60°C for 3 ~ 5 min → acid Washing; 
Immersing with 15% sulfuric acid and 0.2% inhibitor solution at room temperature for 2h → water washing; 
Rinsing residual acid and ink ash on the inner and outer walls of the tube with water not lower than 0.5 MPa, so that the pH reaches 6-7 , rinsing → neutralization; 
Immersed in 5% to 6% uranium carbonate at room temperature for 10-15 minutes → water washing; 
Conditions as above → nitric acid 18% → chromic anhydride 5% to 6% immersion for 1-2 minutes to ash → chromic anhydride 20%→25% immersion for 1~2h for the second time ash→water washing; 
Immersion for 2~3min under normal temperature conditions,→passivation; 
Dynamic immersion for 10~15min with sodium nitrite 5%~6%, sodium hydroxide 3% → Hot water washing; 
Repeatedly immersed in hot water of 50°C - 60°C for 15 min → drying; 
Rapid drying with clean hot compressed air → inspection; 
Visual inspection of the inner and outer surfaces of the tube, available hands Tube irradiation or anatomical inspection of the inner cavity of the tube can also be wiped with a white cloth, no obvious rust and black ash → sealing; 
The tube is first covered with a layer of plastic cloth and then a layer of recycled cloth → brush primer; 
Immediately brush the first primer → storage Seamless pipe pickling passivation; 
The acid-washed passivated tube is placed in a dry and well-ventilated place to prevent excessive humidity or rain, so as to avoid rust again. 


Pickling passivation seamless steel pipe must pay attention to matters

a. Pickling solution and passivation solution should be checked frequently, and the content should be determined. Always keep the specified content (measured in the pickling tank and the passivation tank at 4 points, and analyze the acid solution and the passivation solution. If the content is not enough, Will affect the pickling passivation effect).
b. When pickling, it is strictly forbidden to mix the acid solution with the neutralizing solution and the passivation liquid. Especially when mixed with the passivation solution, it will produce a highly toxic chlorine-containing gas, which seriously pollutes the environment and affects the health of the operator.
c. Pickling and passivation work must be carried out continuously in steps and cannot be stopped in the middle.
d. Pickling solution and passivation solution should not be discharged arbitrarily. Because it contains chloride ions and carbonate ions, if it is not handled well, it will cause great damage to crops. Therefore, it is necessary to neutralize the acid solution and the passivation solution, and the pH can reach the discharge standard before it can be discharged.
e. The disadvantage of the pickling and derusting process is that the rust-removed pipe will be re-rusted after drying, although it is repeatedly washed by hot and cold water, if it does not cover the primer quickly (or other surface treatment) Corrosion is becoming more and more serious with the extension of time, so it is necessary to passivate after pickling, so that it can form a thin passivation film on the steel surface to protect the passivation of the seamless steel pipe. effect.
f. The speed of pickling and derusting of steel pipes should meet the general requirements. There is no "over-corrosion" phenomenon. If the pickling time is too long, it will destroy the smooth surface of the steel.
g. The materials used in the pickling, passivation and degreasing process of the pipes are all corrosive, toxic and explosive chemical solvents, so the operator must abide by the relevant anti-corrosion, anti-virus and fire-proof operating procedures.


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