Influence of Corrosive Atmosphere on Aging

SO₂ Sulphur dioxide

Corrosion of silver, aluminum, and bare copper

Phenomenon accelerated by high temperature and relative humidity.

• Blackening of exposed silver surfaces

• Appearance of dendrites on electronic and power circuits

• Increased resistance of disconnecting contacts exposed to air

• Excessive device temperature rise

• Short-circuiting of circuits resulting in non-operation of the control unit

• 3C1: 0.037

• 3C2: 0.11

• 3C3: 1.85

• 3C4: 4.8

H₂S Hydrogen sulphide

Sulphurization of silver. Phenomenon accelerated by high temperatures.

• Major blackening of exposed silver surfaces

• Appearance of dendrites on electronic and power circuits

• Increased resistance of disconnecting contacts exposed to air

• Excessive device temperature rise

• Short-circuiting of circuits resulting in non-operation of the control unit

• 3C1: 0.0071

• 3C2: 0.071

• 3C3: 2.1

• 3C4: 9.9

Cl₂ Chlorine

Corrosion of metal parts

• Oxidation

• Inter-granular corrosion of stainless steel

• Increase in friction

• Possibility of mechanical rupture

• Breaking of stainless-steel springs

• 3C1: 0.034

• 3C2: 0.034

• 3C3: 0.1

• 3C4: 0.2

NH₃ Ammoniac

• Attacks polycarbonates

• Corrodes copper

• Cracking of polycarbonates

• Blackening of copper

• Possibility of rupture

• Increased temperature rise

• 3C1: 0.42

• 3C2: 1.4

• 3C3: 14

• 3C4: 49

NO₂ Nitrogen oxide

Corrosion of metal parts

Oxidation

Increased temperature rise

• 3C1: 0.052

• 3C2: 0.26

• 3C3: 1.56

• 3C4: 5.2

Oily atmospheres

Attacks polycarbonates

Cracking of polycarbonates

• Possibility of rupture

• Increased temperature rise

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(1) ppm = parts per million in volume

3C1

Rural zones or urban zones with low industrial activity

Negligible

No impact on service life because concentrations are very low.

Implement the standard program.

No particular recommendation

3C2

Urban zones with scattered industrial activity and heavy traffic

Low level

Moderate impact on service life.

Implement the standard program.

No particular recommendation

3C3

Immediate vicinity of industrial pollution

Example: paper mills, water treatment, chemicals, synthetic fibers, smelting plants

Significant level

• Major impact on device service life, particularly concerning temperature rise.

• No impact on electronic components with varnished boards.

Implement the standard program.

No particular recommendation

3C4

Inside polluting industrial premises

Example: paper mills, water treatment, chemicals, synthetic fibers, smelting plants

High level

• Significantly reduced service life if no particular precautions are taken.

• For electronic systems, no impact on varnished boards and gold-plated contacts

• Carry out more frequent periodic checks.

• Change the grease on the disconnecting contacts by Condat Pyratex EP2 fluorinated grease.

• Install the switchgear in a room offering protection from the pollution

• Use fixed rather than drawout devices