“EP Technology ™”
Stainless Steel Electrocleaning, Passivating and Polishing System
Traditional electropolishing processes are effective methods of surface cleaning, which result in removing oxides and iron from the metal surface. They improve the Cr-Fe ratio of the surface layers and alter the surface appearance by smoothing (electrochemically polishing) the surface. These processes, while reasonably effective:
The Electropolish - EP Technology™ advantage….
Clean, Passivate & Polish
The benefits of using EP Technology™
also include the ability to electroclean and Passivate effectively and rapidly without any
noticeable etching or polishing of the component surface.
Excellent high finishes:
Electropolishing with EP Technology™
provides the highest quality electropolished surfaces, along with excellent surface smoothing
resulting in extremely high Cr-Fe ratios and capable of producing an RA
improvement of up to 60%.
Proven, cost effective performance:
The EP Technology™
process is well proven over the past 12 years with
installations in Australia, New Zealand and USA. It is now being made
available for Electrocleaning and electropassivation as well as
Safe and environmentally friendly:
The key benefit of EP Technology™ is that it is safe, cost effective and environmentally friendly. It uniquely addresses both OH&S and EPA compliance costs, as well as bath monitoring and maintenance costs.
Stainless Steel Electro-Cleaning
Cleaning methods for stainless steels
Stainless Steel is often chosen for industrial and architectural
applications because it withstands corrosion, is long lasting, easily
fabricated, requires minimal maintenance and looks good.
Figure 2. Seaside balustrade cleaned using the Electropolish process, giving long term corrosion resistance
The process is benign, safe to the materials being treated, safe for the operator and the environment. There are no noxious fumes and it is totally silent. Unlike traditional abrasive or acid cleaning methods there is no scratching, discolouration or etching of the surface.
At Electropolish we are proud to have developed an effective cleaning solution for architectural stainless steel. Our process is now well proven on major infrastructure restoration projects. We have confidence in our ability to provide an excellent solution, backed with experience and friendly service.
Cleaning methods for stainless steels
The traditional methods of treating surface corrosion of stainless steels
utilise either mechanical cleaning, application of various acid solutions or
electropolishing (3). ASTM A380 and ASTM 967 standards provide a series of
options for cleaning and passivation of stainless steel surfaces, including
Mechanical linishing, buffing and polishing is generally slow, dirty, noisy,
labour intensive and expensive.
Acid pickling and passivation(4) can be achieved by either immersing the
component in a bath of mixed Nitric and Hydrofluoric acids for a significant
time or applying commercially available “Pickling” or “Passivation” pastes. In
general these solutions are highly effective in dissolving surface rust, iron
contamination and oxidation products. Generally, acid pickling can return the
corrosion resistance to the same level as the original parent metal.
Electropolishing is an effective method of surface cleaning, which also results
in removing oxides and iron from the metal surface. It also preferentially
dissolves iron and hence improves the Cr-Fe ratio of the surface layers. It
alters the surface appearance by smoothing, “electrochemical polishing” of the
surface significantly improves the corrosion resistance.
Electrocleaning is based on a similar process to electropolishing but it is
portable and applied locally. This process has significant advantages over each
of the above methods if applied correctly. Firstly, there is no dirt, buffing
compounds or noise involved. The surface appearance is not altered by either
mechanical abrasion, etching or polishing, it is simply returned to its original
condition, clean and bright.
Passivation is the process of forming a natural, protective, corrosion resistant
layer on stainless steel surfaces.
This is promoted by cleaning the surface of dirt, grease & oil, salts and iron
contaminants. Water, detergents and mechanical cleaning techniques can readily
remove dirt, oils and salts on the metal surface. Iron and iron oxides are not
so readily removed with standard cleaning methods, hence pickling and
passivating solutions containing phosphoric, citric, nitric and hydrofluoric
acid are often used for this purpose.
How our process works
The electrochemical cleaning process
The Electropolish process involves applying an electric current through an
electrolyte to the work piece in order to clean the metal surface, Figure 3. The
electrochemical process itself is not new and is rather simple.
Figure 3. Electrochemical cleaning process
The Electropolish process has involved significant development of each aspect of the process, especially the ability to clean large and complex surfaces quickly and efficiently without etching or visibly altering the surface condition.
What it does
Our process performs several functions in the one operation:
Figure 4. Balustrades cleaned using the Electropolish process.
What it does not do
Any pre-existing defects such as scratches or pits from prior corrosion, will be
treated, but not removed.
Fig 1: Electrochemical measurement of a stainless steel tube.
Electrolytes of 1.0M and 5.0M NaCl solutions are prepared from distilled water
and reagent grade chemicals. All potentials are referred to saturated calomel
electrode (SCE). Prior to testing the surface is cleaned with ethanol. The
surface is locally contacted by the electrolyte and is controlled by an
electrochemical control unit.
Once calibration is completed, the
instrument decreases the potential by 120 mV. By running potentiostatic tests
for 10 seconds, the relative corrosion resistance is determined. Typical results
are shown in Fig. 6. If the current shows typical passive behaviour it can be
concluded that the tested area exhibits a pitting potential that is comparable
or higher than the area where the instrument was calibrated. If the current
shows a strong increase, it can be concluded that pitting is initiated. Hence,
the tested area exhibits a corrosion resistance that is significantly decreased
compared to the area where the calibration was performed.
The above technique, as well as direct determination of the pitting potential have been used extensively in the determination of the appropriate processes for surface preparation, electrocleaning, neutralisation and rinsing.
Comparison with alternative cleaning methods
Utilising the electrochemical test technique described above, the effectiveness
of several standard cleaning methods used on stainless steels has been compared.
The results are summarised in Figure 7.
Figure 7. Comparison
of the corrosion resistance of different cleaning methods.
Cleaning of weldments
Cleaning of stainless steel weldments is important in order to achieve adequate corrosion resistance after welding with particular emphasis being given to the Heat Affected Zones (HAZ). Methods such as mechanical and chemical cleaning are typically used. Electrochemical methods have also been employed where pickling pastes are considered dangerous for OH&S reasons.
Figure 2. Surface oxidation, depleted zone and interference colours of stainless steel welds
The high temperature heat affected zones (HAZ)
of weldments are considered (1) to be chromium depleted, with an attendant
reduction in corrosion resistance. The surface oxidation and chromium depleted
zone and interference colours are represented in Figure 2.
Testing was conducted to identifying the corrosion resistance of the different parts of the weldment, using some common methods of treating the welds. The material tested was standard 2B mill finish grade 316L stainless steel.
• Mechanical cleaning was conducted by buffing using a 3M Scotchbrite pad.
• Acid cleaning was performed using pickling paste of 15% phosphoric acid and 0.9% Hydrofluoric acid.
• Electrocleaning was performed using the Electropolish portable electrocleaning process.
Post weld cleaning
Corrosion tests were also conducted on weldments. The parent metal, low
temperature HAZ, high temperature HAZ and weld metal, were tested after various
forms of cleaning.
Figure 5. Effect of cleaning methods on a stainless steel weldment.
Pickling with commercial pickling paste
significantly improves the corrosion resistance compared with that of the
as-welded material. The electrocleaning process not only recovered, but can
improve the corrosion resistance to a level above that of the original parent
It is concluded that electrocleaning is at least as good as pickling and can even improve the corrosion resistance of weldments.
It is fast and efficient when compared with
pickling and suffers none of the drawbacks of the existing methods. The
Electropolish system offers significant operational cost savings as well as
greatly reduced OH&S requirements.
Safe and environmentally friendly:
A key benefit of the Electropolish system is that it is safe, cost effective and environmentally friendly. It uniquely addresses both OH&S and EPA compliance costs, as well as bath monitoring and maintenance costs.
(1)The ec-pen in quality control: Determining the corrosion resistance of stainless steel on-site
M. Büchler, C.-H. Voûte, D. Bindschedler, and F. Stalder
SGK, Swiss Society for Corrosion Protection, Technoparkstr. 1, CH-8005 Zürich, Switzerland
(2) Estimating the Pitting Resistance of Low-Alloy Stainless Steels
M. Berner, & S. Mischler, Laboratoire de Métallurgie Chimique, Ecole Polytechnique Fédérale de Lausanne
C.-O. A. Olsson, Avesta Research Centre, Outokumpu, Sweden
Australian Stainless Steel Development Association ASSDA website:
(3) Surface treatments
(4) Pickling and passivation
(5) 2B, 2D and BA Cold Rolled Finishes
(6) Crevices and Corrosion
(7) Stainless Steel Fabrication: Common Traps to Avoid
(8) Surface Finish No.4
(9) Fabrication and Special Finishing Methods
(10) Preventing coastal corrosion - teastaining