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LP 900-050

Contact Corrosion

Unbenanntes DokumentIn choosing a KOENIG Expander® you must consider that the material of the sealing plug and the material of the production piece can show different electrical potentials. In the presence of an electrolyte (e.g. 5% Water-NaCi solution), this potential difference causes electrochemical attack on the least noble of the metals in contract - galvanic corrosion. In this case, either the base material or its surface protection will become the anode and will be transferred to the pure metal of the cathode. The corrosion speed or the current density will be determined by the relative surface area or volume of the anode and cathode as illustrated below.

  Cathode
     
  Anode
Large Anode Area → Low Current Density at the Anode → Slow CorrosionSmall Anode Area → High Current Density at the Anode → Fast Corrosion

Effect of Galvanic Corrosion

The following table shows the expected galvanic corrosion behavior of KOENIG Expander®s in common base materials allowing for the relative surface areas of both metals, which influences the speed of corrosion.

  KOENIG Expander® series
Base Material MB 600 MB 700 MB 850 SK HK 55 LP 900 LK 600 LK 950
Steel, carbon/low alloy, plain
2
2
2
2
2
2
2
2
Steel, carbon/low alloy, Zn plated, chromate
2
2
1
2
2
2
2
2
Steel, carbon/low alloy, phosphatized
2
2
2
2
2
2
2
2
Nitrided or case hardening steel
behavior depends on the method used
Stainless steel, DIN 1.4305, AISI 303
1
1
3
3
3
2
1
3
Stainless steel, DIN 1.4005, AISI 416
1
1
3
3
3
2
1
3
Cast iron, GG DIN 1691, plain
2
2
2
2
2
2
2
2
Cast iron, GG DIN 1691, Zn plated, chromate
2
2
1
2
2
2
2
2
Cast iron, GG DIN 1691, phosphatized
2
2
2
2
2
2
2
2
Ductile cast iron, GGG DIN 1693, plain
2
2
2
2
2
2
2
2
Ductile cast iron, GGG DIN 1693, Zn plated, chromate
2
2
1
2
2
2
2
2
Dual cast iron, GGG DIN 1693 phosphatized
2
2
2
2
2
2
2
2
Aluminium alloy,          Ws-Nr. 3.3211, AA 6061
2
2
2
2
2
2
2
2
Aluminium alloy,          Ws-Nr. 3.0615, ~AA 6262
2
2
2
2
2
2
2
2
Aluminium alloy,          WS-Nr. 3.1354, AA 2024
2
2
2
2
2
2
2
2
Aluminium alloy,          WS-Nr. 3.4365, AA 7075
2
2
2
2
2
2
2
2
Cast aluminium alloy, WS-Nr. 3.2371, AA 356-T6
2
2
2
2
2
2
2
2
Cast aluminium alloy, Ws-Nr. 3.2373
2
2
2
2
2
2
2
2
Cast aluminium alloy, Ws-Nr. 3.2381
2
2
2
2
2
2
2
2

Key to the galvanic corrosion behavior of KOENIG Expander®s in the presence of an electrolytic medium installed in base materials per the above table:

1. Not accelerated
2. Lightly accelerated
3. Accelerated

Suggestions to prevent galvanic corrosion

  • Chose materials with no or low potential difference.
  • Use corrosion reducing designs, i.e. if possible prevent the accumulation of fluids on the outer surface of the workpiece.
  • By using suitable surface coatings, corrosion attack can be considerably reduced..

Salt spray testing per DIN 50021 can be done in our lab.


Subject to technical alterations.