1. Dipping method:
Stainless steel pipelines, elbows, small pieces, etc. are most suitable for this method, and the treatment effect is the best. Because the treatment part can be fully immersed in the pickling passivation liquid, the surface reaction is complete, and the passivation film is dense and uniform. As the reaction concentration of the solution decreases, new liquid is continuously replenished. Its shortcomings are limited by the shape and capacity of the acid tank. It is not suitable for large-capacity equipment and pipelines that are too long and too wide. Long-term use will not reduce the effect due to solution volatilization and other reasons. A special site, acid tank and heating equipment are required.
2. Paste method:
Stainless steel pickling passivation paste is currently widely used in China and is supplied by a series of products. The main components are composed of nitric acid, hydrofluoric acid, corrosion inhibitor, thickener, etc. in a certain proportion. Ship standard "stainless acid pickling passivation paste" CB / T3595-94 has specific inspection rules, manual operation, suitable for on-site construction, suitable for stainless steel chemical ship welding seam treatment, welding discoloration, deck top, corner dead angle, backside of escalator and large area of paint passivation in the tank .
The advantage of the paste method is that it does not require special equipment and venues, no heating equipment, flexible on-site operation, one-time pickling and passivation is completed, and strong independence; the shelf life of the passivation paste is long, and a new passivation paste is used for each application process For sexual use, the reaction will stop after the passivation of the surface layer is completed. It is not easy to over-corrode and is not limited by the subsequent flushing time. Weak links such as welds can also strengthen the passivation. The disadvantage is that the workers have poor operating environment, high labor intensity and high cost, and the treatment effect on the inner wall of the stainless steel pipeline is slightly poor, which needs to be combined with other methods.
3. Spray method:
It is suitable for pickling and passivation of a single product in a fixed site, a closed environment, or a device with a simple internal structure, such as the spray pickling process on the plate production line. For stainless steel chemical tankers, it can be used for pickling the inner walls of liquid cargo tanks. The advantage is that the continuous operation speed is fast, the operation mode is simple, the corrosion of the worker is small, and the pipeline can be pickled again during the pipetting process. The solution utilization rate is high. This method has many restrictions, such as:
1. All scaffolds in the tank must be removed, the tank and piping system must be cleaned, and there should be no residues or impurities in the pipeline.
2. All deep well pumps, valves, tank washing machines and other liquid cargo systems of the whole ship must be debugged and ready for use.
3. If the pickling liquid stays in the cabin for a long time, the reaction will cause excessive corrosion of the stainless steel. Therefore, it must be continuously operated. The shipyard must cooperate highly and prepare a large amount of cleaning water at any time. as a result of.
4. The waste acid and waste water discharge must be placed in a larger container or temporarily replaced by a tank, but should be neutralized and discharged as soon as possible to avoid corrosion of the cabin.
5. With the increase of reaction time and the increase of solution impurities, the effective components of the pickling solution gradually decrease, and the concentration of the solution must be checked at any time and the new solution must be added in time.
6. The residence time of spray liquid on the deck, the four walls, the dead corner, the back of the escalator and other parts is shorter, and the pickling effect is slightly worse than the bottom plate.
