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What kind of corrosion and erosion are there?

Posted on: 17th, April 2018

Corrosion and erosion can weaken the structural integrity of a pipeline and make it an unsafe medium for transporting potentially hazardous materials, which our UT5000 Gauge can identify.

What kinds of corrosion and erosion are there?

Uniform Corrosion

This form of corrosion can also be called general corrosion, and is the most common form of corrosion. It is caused by several individual electrochemical processes that occur consistently over the whole of the surface considered. The problems caused by this type of corrosion are;

  • Loss of metal thickness
  • Loss of weight per unit

Pitting Corrosion

This form of corrosion is particularly menacing. The attack is in the form of highly localized holes that can penetrate inwards extremely rapidly, while the rest of the surface remains intact. A component can be perforated in a few days with no appreciable loss in weight on the structure as a whole.

When looking at pitting and the way in which it works, it is most aggressive in solutions containing chloride, bromide or hypochlorite ions, opposed to Iodides and fluorides which are significantly less harmful. Stainless steels are particularly sensitive to pitting corrosion, but other metals, such as passive iron, chromium, cobalt, aluminium, copper and their alloys are also prone to this form of damage.

Erosion-corrosion

This is caused by the flowing movement between a corrosive fluid and a metal surface. This process leads to the formation of grooves valleys, wavy surfaces and holes. Each form of this type of corrosion will have a directional appearance on the metal surface that will mimic that of the fluid. Most metals and alloys can be affected, particularly soft materials (e.g. copper, lead, etc.) or those whose corrosion resistance depends on the existence of a surface film (aluminium, stainless steels).

This form of corrosion will be particularly worse in two-phase liquids (containing suspended solid particles or gas bubbles), the impact of the particles can damage or even eliminate the protective layers or passive films that are normally stable in the absence of particles, and the local corrosion rate is then markedly accelerated. This phenomenon is called abrasion-corrosion.

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