Fabricators have traditionally applied pickling paste after welding stainless steel to restore the oxide film that gives stainless steel its corrosion resistance. Pickling paste is often a cocktail of nitric acid and hydrofluoric acid, which is considered to be highly dangerous and toxic.
As an alternative to pickling paste, Metal Science Technologies have released mepBLITz, a mobile electrochemical machine that electropolishes the welds. The mepBLITz is an industrial mobile electro-polishing machine, which uses a food grade phosphoric acid with several sequestering agents for polishing.
The hydrofluoric acid in pickling paste can penetrate the skin and deeper tissues, binding to calcium and causing tissue damage, including decalcification of bone, if immediate first aid measures are not taken. Symptoms of exposure to hydrofluoric acid may not be immediately evident but can be fatal. Hydrofluoric acid penetrates tissues quickly and interferes with nerve function. The resulting burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.
Pickling paste is prohibited for OH&S reasons on many commercial sites but it is still used by fabricators as there is no viable labour-efficient alternative.
The mepBLITz at 2400watts works quickly and has a cooling system and can be used straight onto hot welds, which further increase its speed. The mepBLITz works on TIG and MIG welds. The correct OH&S requirements for workers handling pickling paste are onerous in process, time and cost, and while they reduce the health risk they do not remove it. There are a number of restrictions on storage and use of pickling paste. The pickling process should generally include a pre-treatment, an after-treatment and a waste treatment in order to reach the required result and meet the environmental requirements.
Scanning electron microscopy has shown that pickling paste chemicals have an etching effect and can increase the surface roughness profile, resulting in an obvious contamination problem. This can appear to the naked eye as a dull stain. An effective way to post-weld finish stainless steel is electro-polishing. Electro-polishing is an electrochemical process that increases the density of chromium throughout the weld surface and has the ability to create the oxide film. Electropolishing provides maximum dense and durable passive film.
The mepBLITz is considered to be safe, rapid and convenient, providing the stainless steel fabrication industry an alternative to the traditional pickling and passivation methods or the mechanical removal by linishing.