Correctly assess and analyze surface changes in pitting corrosion
- Aaron Papadopoulos
- Jun 16
- 2 min read
In practice, changes can occur on the surface of medical devices over time due to mechanical, chemical, and/or physical (e.g., thermal) influences. The causes of these surface changes, unless they were already caused during use, are usually to be found in the reprocessing process. If surface changes occur, a systematic approach must be taken to eliminate and prevent them:
Determine the type, origin, and cause
Assess the risks
Implement the manufacturer's recommendations for elimination, if necessary
Initiate preventative measures, followed by a requalification if necessary
The above-mentioned systematic approach is used to describe the most common surface changes in metallic instruments made of stainless steel (SR steel) and/or plastic or rubber products.
Checklists help to guide with a systematic approach:
Pitting Corrosion on Metallic Surfaces
SR steel can develop pinhole-like corrosion pits, which are often microscopic and surrounded by reddish-brown or iridescent corrosion products. These deposits are usually arranged in a circle around the pit. Do not confuse these with material-related cavities or foreign inclusions in inferior steels, or with contact corrosion in stainless steel/stainless steel material combinations.
Type of surface changes, origin, and causes
Pitting corrosion in stainless steel is caused by the action of halide ions (bromides, iodides), especially chlorides. These ions can locally penetrate the passive layer of instrument steels and initiate the formation of corrosion pits. Persistent organic residues such as blood, pus, or secretions can also be a cause.
A concentration or drying of chloride-containing liquids can be responsible for pitting, for example, due to an excessively high chloride content in the final rinse water or due to physiological saline solutions on instruments. Another cause can be found in brand-new instruments – due to the even thinner passive layer, these are more sensitive to chloride-containing media than instruments that have been in use for longer and have a built-up passive layer.
Recommendations for Removal
Using an acidic basic cleaner according to the manufacturer's instructions allows the corrosion products to be dissolved. Remaining corrosion pits should, if necessary, be removed by mechanical reconditioning at the manufacturer's or repair service. In cases of deeper pitting corrosion, permanent repair is often no longer possible – in this case, the instrument must be replaced.
Prevention Measures
Chloride-induced pitting corrosion can be largely avoided by using low-chloride water, minimizing organic residues, or other influences from chloride-containing liquids, such as physiological saline solution on instrument steel.
Assessment of Potential Risks
For patient and user safety, affected instruments must be immediately removed from the instrument cycle. To maintain the value of the instruments, it is necessary to eliminate the cause of pitting. Corrosion pits pose a hygiene risk and can be the starting point for stress corrosion cracking.
want to know more? Then directly get access to chapter 12 of our red brochure in its current edition:
About the author
Aaron Papadopoulos is a member of the AKI since 2018 and is one of the representatives of the process chemical manufacturers in the group. He works within Ecolab Deutschland GmbH in Strategic Marketing for the Healthcare Division taking care of endoscopy and instrument reprocessing.
Commentaires