Understanding corrosion
Corrosion of an instrument is almost never an isolated accident: it is the meeting of a material, a geometry, a medium and a stress. This module explains the five mechanisms encountered in central sterilization.
Educational content. It does not replace or modify the current MEDLANE instructions for use supplied with the devices: the applicable pre-disinfection, cleaning, disinfection, drying, lubrication and sterilization parameters are stated there, and nowhere else.
Recognising what is at work
Each mechanism is described on the same grid: what it is, where it may appear, contributing factors, prevention principles.
Crevice corrosion
- What it is
- Localised attack developing in a confined space where the medium stagnates and where the passive layer no longer regenerates under the same conditions as on a free surface.
- Where it may appear
- Interstices of an architecture: joints, overlapping areas, underside of a ratchet, contact between two assembled parts.
- Contributing factors
- Stagnant medium in an enclosed space.
- Residues left in hard-to-reach areas.
- Prolonged residual moisture.
- Prevention principles
- Handle articulated instruments in the open position so that interstices remain accessible.
- Avoid any prolonged storage in a damp state.
Galvanic corrosion
- What it is
- Attack appearing when two materials of different natures are in electrical contact within the same conductive medium: the less noble one is preferentially attacked.
- Where it may appear
- Contacts between dissimilar materials, in particular when they are gathered in the same tray or container in a damp environment.
- Contributing factors
- Contact between materials of different natures.
- Simultaneous presence of a conductive medium.
- A damaged instrument mixed with sound instruments.
- Prevention principles
- Avoid prolonged direct contact between dissimilar materials during reprocessing.
- Isolate an instrument showing surface alteration before returning it to the cycle.
Pitting corrosion
- What it is
- Point-wise breakdown of the passive layer producing a narrow cavity that progresses in depth, often without visible alteration of the surrounding surface.
- Where it may appear
- Exposed surfaces, areas where a droplet or deposit remained in place until drying.
- Contributing factors
- Media containing halide ions.
- Drying of a deposit or droplet on the surface.
- Locally degraded surface condition.
- Prevention principles
- Remove residues before drying and rule out media that are aggressive to the passive layer.
- Control the quality of the water used at the end of the cycle, in accordance with the instructions in force.
Intergranular corrosion
- What it is
- Attack favouring the grain boundaries of the metallic structure, originating in the metallurgical and thermal history of the material rather than in its use.
- Where it may appear
- Areas subjected to heat input, in particular near assemblies.
- Contributing factors
- Uncontrolled heat input on the part.
- Material composition and treatment.
- Prevention principles
- It is prevented in manufacturing, through grade selection and control of heat treatments, not through reprocessing.
Stress corrosion cracking
- What it is
- Cracking resulting from the combined action of a sustained mechanical stress and a corrosive medium: neither alone would be sufficient.
- Where it may appear
- Areas under permanent tension: branches held closed, constrained joints, fillet radii.
- Contributing factors
- Mechanical stress sustained over time.
- Corrosive medium present at the same time.
- Prevention principles
- Do not reprocess or store a ratcheted instrument closed under load.
- Report any crack found at inspection and withdraw the instrument from the cycle.
General principles. No concentration, duration, temperature or product grade is published here: such values belong to the current MEDLANE instructions for use and to the facility's own procedures.
Naming before concluding
Six observation categories, with no diagnostic conclusion: an alteration is qualified on the part itself, with a verified source image. No damage photograph is published until a real, validated MEDLANE image exists.
Discoloration
Change in surface tint, with no apparent loss of material.
Illustration pending
Pitting
Point-wise cavities, sometimes isolated, on an otherwise intact surface.
Illustration pending
Deposits
Material added to the surface, whose origin must be identified before any conclusion.
Illustration pending
Scratches
Linear mechanical marks altering the surface condition.
Illustration pending
Joint damage
Excessive play, stiffness or irregular movement.
Illustration pending
Corrosion
Alteration of the metal surface itself, to be qualified according to the mechanism.
Illustration pending
What is examined after cleaning
An educational reading of MEDLANE's documented inspection: it describes observation points, not release criteria.
- 01Visible cleanliness of surfaces, joints and serrations
- 02No bent, broken, cracked or worn parts
- 03Unobstructed cannulas and trocars
- 04Continuous edges, free of nicks
- 05Smooth articulation without excessive play
- 06Correct operation of locks and ratchets
- 07Correct reassembly of dismountable instruments
- 08Condition of the cutting edges
MEDLANE documentation · Notice d'utilisation MEDLANE — dispositifs médicaux ré-stérilisables (version 15) · 2020-09
Not all laser processes are equivalent
Technical literature warns generically against laser engraving processes liable to alter an instrument's surface. That generic warning does not describe the MEDLANE process.
MEDLANE marking is performed in-house by a thermal annealing process, which creates contrast without removing material — to be distinguished from engraving, which removes material from the surface. The processes do not have the same effect on the part and cannot be treated as equivalent.
See the MEDLANE marking process →