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Corrosion of Roller Shutter WhatsApp Image 2020-05-08 at 12.30.49 PM, HEW…

- - - - Normally made of Aluminum Alloy
        
        High strength-to- weight ratio
        
        Light weight
        
        Resilient
- - - - Depassivation of film on the metal surface
      - Presence of aggresive ions
        
        Halogen ions such as Chloride ions, Cl⁻ from the rainwater
      - Stagnancy of electrolyte
        
        Rainwater or chemically active electrolytes remain still on parts of the roller shutter
- - - - Observe the corrosion condition to differentiate type of corrosion experienced by the roller shutter
  - - - Utilizes ultrasound waves by transmitting and receiving the sound waves on the roller shutter and analyze the the reflected sound energy to detect the shape, location and depth of the pits
        
        Calculation of pitting factor
        
        Pitting factor = P/d
        
        P= deepest pit length, d = penetration thickness average of uniform corosion
- - - - Passive film breakdown sue to corrosion potential increases ⩾ Eₚᵢₜₜ
        
        Pitt growth
  - - - Anodic region inside the pit is formed and cathodic region outside the pit
        
        Excess positive charge inside pit is then balanced by migration of aggressive ions into the pit
        
        Fe²⁺↔Cl⁻
        
        Metal ions diffuse outward and H⁺ ions diffuse inward
        
        Increase in acidity inside the pit
- - - - e.g. Stainless Steel
  - - - Prevent moisture and oxygen from reacting with the metal
  - - - reduce high energy sites that promote chemical reaction