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Metal / Corrosion - Pitting Corrosion

Type of Surface Change

Pinprick-like corrosion holes in stainless steel, frequently surrounded by microscopically small, sparkling, reddish-brown or multi-color corrosion spots, often associated also with circular corrosion deposits around the corrosion hole. (Not to be confused with material-specific cavities or foreign-matter inclusions that may occur in minor-quality instrument steels, or with contact corrosion symptoms when only stainless steel instruments are used.)
     
Origin & Causes        

  • In stainless steels, caused by exposure to halide ions (bromides, iodides), especially chlorides that locally break through the passive layer of instrument steels, thus causing pitting.
  • Frequently, pitting is due to the use of liquids with a high chloride content or, specifically, to dry residues of such liquids adhering to the instrument surfaces, e.g. if the final rinse water contains too many chlorides or if saline residues remain on the instruments.
  • Brand-new instruments are particularly susceptible to attack by media containing chlorides due to their still thin passive layer, while instruments that have been in use for some time are more resistant because they have developed a thicker passive layer.

Treatment Recommendations       

Corrosion products can be dissolved with an acid-based cleaner in accordance with the manufacturer's instructions. The remaining corrosion holes may be treated mechanically (reworking either by the manufacturer or a qualified repair service provider). 

Preventive Measures       

Chloride-induced pitting can usually be prevented by using low-chloride water and minimizing instrument exposure to other liquids containing chlorides, such as saline solutions.

Risk Assessment        

  • Severely corroded instruments should be immediately withdrawn from service (and the instrument processing cycle) for reasons of patient and user safety!
  • To retain your instruments' value, the causes of pitting corrosion must be eliminated.
  • Corrosion holes can pose a hygienic hazard and may lead to stress corrosion cracking as well.