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Metal / Corrosion - Contact Corrosion

 Type of Surface Change        

  • When using only stainless steel instruments (stainless steel = standard non-rusting/rustproof steel, also known as surgical stainless steel), small dot-type or ring-shaped, brownish-blue discolorations with slight corrosion in the contact areas can occur. This type of contact corrosion is frequently mistaken for pitting. Upon closer examination, however, it becomes clear that there is no hole in the center of the corrosion spot. Rather, the surface structure is slightly rubbed smooth in these places.
  • However, the classic variant of contact corrosion occurs in a material combination involving stainless steel and non-ferrous metals (German silver, brass, copper). Depending on the situation, this leads to corrosion deposits in the contact areas and, mostly, beyond them.

Origin & Causes        

  • When using only stainless steel instruments, contact corrosion has so far been observed only after the washing cycle. Microfriction at the contact points leads to partial abrasion of the passive layer. Thus, the corrosion protection is temporarily removed in these places, which in turn leads to the surface changes described above. (This surface change could easily be classified also as "fretting corrosion".)
  • In the classic material combination (stainless steel in contact with non-ferrous metals), when the instrument stock typically contains old and new instruments, this type of corrosion occurs during cleaning as well as during sterilization due to a damaged and/or non-closed chromium or nickel layer (e.g. in the case of hollow handles or retractors).

Treatment Recommendations        

  • When only stainless steel instruments are used, there is no need to remove contact corrosion symptoms because such surface changes, due to their low severity (i.e. quantity of deposits involved), pose no risk either to the affected instruments or to other, unaffected items. Experience shows that such surface symptoms usually disappear after a few processing cycles. If acid media (neutralizing agents) are used, these deposits usually dissolve at once, which in turn accelerates the passivation process.
  • If contact corrosion occurs as a result of protective layer damage in nickel- or chromium-plated instruments, there is usually no remedy (for example, in the form of repair).

Preventive Measures        

  • Avoid vibration when cleaning stainless steel instruments (e.g. by ensuring that the cleaning/disinfecting apparatus, or washer-disinfector, stands firmly on level ground).
  • Replace nickel- or chromium-plated instruments with severely damaged (scaly, peeled-off) protective layers with stainless steel instruments at once.

Risk Assessment        

  • As experience shows, no risks exist either for affected or for unaffected items when only stainless steel instruments are used, since the low amount of deposits is insufficient for causing damage. Neither is there any patient hazard in this case.
  • However, when both stainless steel and non-ferrous instruments are used, considerable damage can be caused to intact instruments, depending on the extent of the protective layer damage involved.
  • Damaged instruments may cause allergenic reactions (nickel allergy) if deposit particles of sufficient quantity come off and remain in the wound.