Carbon steel and copper
Iron oxides (rust), welding skin, mill scale and annealing skin. Copper oxides can be removed by adjusting the cleaning method for decoppering (only during post-commissioning cleaning). With post-commissioning cleaning, hardness salts (such as calcium carbonate, lime) are also removed.
Cleaning with inhibited hydrochloric acid is a common method in which the material is completely pickled, and rust, welding and mill scale are removed. If, besides flash rust, older rust is also present (Fe2O3), hydrofluoric acid or another additive is added to prevent corrosion by iron III (Fe3+). The passivation is carried out with ammonium citrate and an oxidizer.
During cleaning, a large amount of waste water is generated because of the the intermediate rinsing phases, which can be processed using the DND principle (Detoxification, Neutralization, Dewatering).
- Removes iron oxides (rust) as well as welding skin, mill scale and annealing skin;
- Lower operating temperature (40-50°C);
- Very suitable for heavily rusted material;
- Can dissolve copper oxides if present (by means of an adjusted cleaning procedure);
- In some cases, the only suitable method.
- Large amounts of waste water;
- Use of corrosive chemicals during the pickling step;
- Cannot be used if stainless steel material is present;
- Cannot be used on higher alloyed steels that include chromium or P91/P92;
- Longer cleaning time;
- Less friendly to people and the environment;
- With incorrect use, there is a risk of corrosion of the base material.