Calcareous

Definition - What does Calcareous mean?

Calcareous refers to a sediment or soil which contains or is formed from calcium carbonate or calcite. Calcareous or calcium carbonate is used to prepare calcareous coatings that are used as a cathodic protection. This coating forms a layer of calcium carbonate and other salts deposited on the substrate's surface. When a surface is cathodically polarized, as in cathodic protection, it forms a layer which is as a result of the increased pH adjacent to the protected surface.

Petropedia explains Calcareous

The chemistry and structure of calcareous depend on its nucleation and growth kinetics, which, in turn, are determined by variables like:

  • Potential
  • Current
  • Time
  • Pressure
  • Temperature
  • Seawater chemistry
  • Velocity
  • Substrate surface condition

When calcium and magnesium are supersaturated in seawater, they form calcium carbonate (CaCO3), magnesium carbonate (MgCO3) and magnesium hydroxide Mg(OH)2. These solid products, known as calcareous deposits, promote a physical barrier against oxygen diffusion, hence decreasing the corrosion rate. The different forms of calcareous deposits have different structure and form under different parameters.

Several factors influence the formation of calcareous deposits, including:

  • Potential
  • Current
  • pH
  • Temperature
  • Pressure
  • Seawater chemistry
  • Flow
  • Time

There is an increasing interest within oil and gas production in placing most of the production on the seabed. In that connection, there is a need for subsea heat exchangers. Normally, materials used underwater are made of steel protected with cathodic protection. Steel is a relatively cheap material. In addition to lowering the immune state potential, the use of cathodic protection leads to precipitation of calcareous deposit, due to increased interfacial pH. This layer functions as a barrier against the corrosive environment, leading to a decrease in current demand.

However, a calcareous deposit also hinders thermal conductivity, which is unwanted in connection to a heat exchanger. Thus, it is important to find a solution in which calcareous deposits do not precipitate on the surface.

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