Corrosion

A common problem affecting power plants in particular

Turbine

Corrosion is a fact of nature – and an expensive one, at that. NACE International, the leading authority on corrosion, initiated in 2002 a study to estimate the costs caused by corrosion in the United States. This study concluded that the overall annual cost amounted to 276 billion dollars (read more here).

In power plants, corrosion is the primary factor leading to costly and critical downtimes. The water-steam circuits in fossil and nuclear power plants are inherently prone to corrosion, as metal components are constantly in contact with water. Measures to monitor or prevent corrosion are crucial in this context.

Metrohm offers a range of instruments and methods for measuring parameters related to corrosion.

Regulatory compliance

As corrosion can occur at any time given the continuous contact between metal parts and water, power plants must closely monitor corrosion. This includes several parameters and indicators.

Various DIN and ASTM standards deal with how this monitoring should be performed. These standards describe in detail how corrosion rates should be calculated and how the electrochemical tests should be performed, among other things.

> Overview of standards relating to corrosion

Causes and types of corrosion

On a metal surface, corrosion as an electrochemical process involves oxidation (e.g., dissolution of the metal) and reduction (e.g., of oxygen). In this process, the corroding metal deteriorates.

Corrosion occurs in various forms and types. Depending on the environment and the physical circumstances, we might observe:

  • uniform corrosion,
  • pitting corrosion (i.e., causing localized pits or pin holes in the material),
  • crevice corrosion (i.e., where a liquid promoting corrosion is stagnant),
  • galvanic corrosion (between two dissimilar metals in a corrosive electrolyte), or
  • microbiologically induced corrosion.
> Metrohm has a series of Application Notes on corrosion. Read more …

Corrosion causation and inhibition

Regardless of the type of corrosion, power plants must ensure that corrosion occurs as little as possible or not at all.

To achieve this, they can, on the one hand, monitor substances and parameters that indicate corrosion, such as conductivity, pH value, or the presence of corroding anions and cations.

On the other hand, power plants can make sure that corrosion inhibitors that are added are present in sufficient amounts (e.g., zinc ions, phosphate, or phosphonates for steel and steel alloys or triazoles for copper and copper alloys).

> Read more about corrosion inhibition

Corrosion monitoring by electrochemistry: Metrohm Autolab solutions

The simplest and most straightforward way to quantify corrosion is to determine the weight loss of a metal sample in the test medium over time. However, this type of testing takes a long time and requires a great deal of work, and extrapolating this weight loss to reliably predict the lifetime of a system is not so easy (e.g., in the case of pitting corrosion).

Electrochemical testing such as linear polarization (LP) and electrochemical impedance spectroscopy (EIS) provides a viable alternative to weight-loss testing. These methods allow quick characterization of electrochemical systems and provide more detailed information about corrosion phenomena.

> Learn more about Electrochemical Impedance Spectroscopy

> Learn more about Metrohm Autolab instruments for electrochemistry

Further applications and products

pH value and conductivity monitoring

The ADI 2045TI Process Analyzer from Metrohm Process Analytics can be used to analyze several parameters in multiple sample streams.

Learn more about the ADI 2045TI

ASTM D8045: Acid number in crude oil

Acidity is conducive to corrosion. Monitoring of the acid number in raw materials therefore helps to prevent corrosion and thus keep maintenance costs low. ASTM D8045 describes the monitoring of the acid number in crude oil and petroleum products.

Learn more …

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