Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers



Last updated: October 29, 2019

What Does Decobaltification Mean?

Decobaltification is a corrosion process in which cobalt is selectively leached from cobalt-base alloys.

It creates problems in the tooling/machining industries where cobalt is leached by many of the amino alcohols and amine-based additives found in almost all water-miscible machining fluids. Cobalt leaching is hazardous to carbide tools as well.

Decobaltification is at the heart of three potentially costly problems:

  • Reduced performance and life of the tool
  • Health problems in some workers, causing dermatitis and respiratory distress
  • Disposal of contaminated wastewater

Corrosionpedia Explains Decobaltification

In the decobaltification process, the less noble metal is removed from the alloy by microscopic-scale galvanic corrosion. A porous material with very low strength and ductility is the result. Regions that are selectively corroded are sometimes covered with corrosion products or other deposits, and since the component keeps the original shape, the attacks may be difficult to discover.

Cobalt alloys are components in tool steels. Stellite is an alloy containing cobalt and chromium, and sometimes other metals. Stellite-type alloys that are used for tools are responsible for:

  • Hardness
  • Wear resistance
  • Excellent cutting

When a tool loses its binder, the surface is weakened and may be subject to accelerated wear. The weakened surface structure compromises the bond between the tool and any coating applied to it.

In the case of hard metal machining, decobaltification can be controlled by adding inhibitors to the fluid, such as triazoles. While this is effective initially, the inhibitor becomes depleted as the fluid is used and loses its effectiveness. However, inhibitors do little to control cobalt leaching during the manufacture of tungsten carbide tools, and during carbide grinding, where metal fines are a problem.


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