Certain types of stainless steel are not suitable for lengthy immersion times in a strong acid pickle for austenitic grades, as they are susceptible to acid attack. Typical materials, subject to over-pickling, are the sulphur containing machining grades (e.g. 303) and low nickel grades (400 series). ANOPOL special pickling solutions are available for these less resistant materials.
A clean stainless steel surface will generate its own passive oxide layer when exposed to oxygen. It is this oxide layer that gives stainless steels their corrosion resistant qualities. It is, however, possible to accelerate the formation of this layer with ANOPOL chemical passivation processing.
Chemical passivation is not always necessary, but is important where surfaces are possibly starved of oxygen, as in the case of pipework or enclosed vessels. Where items are pickled and likely to be employed in corrosive atmospheres, such as components in chemical processing plants, at marine and coastal locations, chemical passivation following pickling is highly recommended. Additional passivation following electropolishing is not necessary due to the excellent oxide layer formation present after electropolishing.
Pickling and passivating of stainless steels is not restricted to immersion in treatment tanks, although this method is widely used. Where fabrications are too large for immersion or require treatment in-situ, ANOPOL spray-on systems can be employed. The results are compatible with the finish obtained by immersion methods.
Where only localised areas require treatment, for example heat affected surfaces resulting from welding; ANOPOL pickling paste products can be applied with a brush.
ANOPOL has extensive pickling and passivating facilities. Additionally, ANOPOL can supply all the necessary equipment, including water treatment, together with the necessary chemicals to those companies wishing to carry out in-house pickling and passivation, or provide resources and trained personnel to complete onsite surface treatment for customers.
Cleaning, pickling and passivating products are available in liquid and gel/paste form.