Electrochemical (anodic) cleaning
Electrochemical (anodic) cleaning of stainless steel surfaces contaminated with rouging is based on the concept of electropolishing.
As a reversal of the electroplating process, electropolishing uses a suitable electrolyte and an application of direct current to remove material (metal atoms) on the µm scale from a workpiece surface, which serves as the anode, by means of electrolytic metal oxidation.
Electrochemical removal processes can be applied successfully and reproducibly in both an immersion bath method and in a suitable wiping technique (as a mobile version). The qualitative surface conditions of stainless steel chambers in terms of corrosion behaviour and cleanability are significantly improved in these controlled electrochemical treatments.
Before any specific on-site cleaning measures are actually carried out, the equipment operator, equipment manufacturer and the technicians from the electropolishing specialist come together in an engineering meeting to plan the technical, safety-related and organisational procedure and discuss the necessary preparations.
Operator representatives in charge of work safety and hygiene are also involved in the preparations, and are given the necessary data and information by the electropolishing specialist.
Because all of the work that needs to be performed is completely isolated by film enclosures installed ahead of time (see Figure 13), this measure can be carried out on a sterilization chamber without interrupting MPPU/CSSD operations, and a full continued supply of sterile goods can be ensured using the other devices.
Electrochemical cleaning involves a controlled wetting of the interior surfaces with a suitable electrolyte using a mobile hand tamping unit in combination with a fleece body and an embedded cathode. In the designated working area of the chamber surface serving as the anode, a time-dependant targeted removal of material from the surface takes place on the scale of 5–10 µm in a controlled electrical anode/cathode field by means of electrochemical oxidation (= electropolishing).
On-site rehabilitation of an interior surface on a chamber using electrochemical (anodic) cleaning
图13b:工作空间划分 Workspace partitioning
The electropolishing process ensures that all films or residues are carefully removed from the stainless steel surface without leaving behind any residues. In addition, and virtually at the same time as the targeted electrochemical material removal, a micro-smoothing of the surface (reduction of surface roughness) also takes place. As a result of this, and depending on the material characteristics (of the original surface), one can usually expect to see a significant improve- ment in surface quality with regard to corrosion-resistance.
Figure 14: Schematic illustration of the surface contour before (dark blue topography) and after (light blue topography) 
在应用电化学物质去除和不锈钢表面无残留清洗之后，随后使用符合DIN EN 285（给水）规范的水进行冲洗步骤。在接下来的工作步骤中，通过湿化学钝化的方式建立了钝化层。在最后一步中，用符合DINEN285规范的水（给水）彻底冲洗腔室，并测量电导以监测清洗过程，清洗溶液的所有剩余痕迹都是安全和经验证已去除。
After the applied electrochemical material removal and the resulting residue-free cleaning of the stainless steel surface, a rinsing step is subsequently carried out with water that meets the specifications of DIN EN 285 (feed water). In the work step that then follows, the passive layer is built up by means of wet-chemical passivation. In a final step involving a thorough rinsing of the chamber with water that meets DIN EN 285 specifications (feed water) and the measurement of electrical conductance to monitor the rinsing progress, all remaining traces of the cleaning solution are safely and verifiably removed.
Throughout the entire procedure, all treatment parameters, such as surface roughness before and after cleaning, temperatures, pH and electrical conductance of the solutions, are documented in detail. Once the apparatus has been functionally re-qualified by the equipment manufacturer, the steam sterilizer can be completely handed over to the customer for use again after a total treatment time of approx. 1–2 days.
Figures 15a and 15b: Steam sterilizer before (left) and after electrochemical (anodic) cleaning (right)
Following completion of the electrochemical cleaning, the chamber's interior surfaces exhibit homogeneous surface conditions with microscopically smooth, reflective/glossy properties. In addition, the surface smoothing which has taken place on a microscopic scale (massive reduction in actual surface area) results in significantly improved corrosion properties and better cleaning behaviour for any new films and discolourations that form in the future.
Electrochemical cleaning also optimises and simplifies the subsequent regular care of a chamber's interior surface.