Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Pitting Factor

Last updated: August 15, 2018

What Does Pitting Factor Mean?

This can be described as the ratio between the depths of the deepest pit of corrosion divided by the penetration average, all calculated from the material's lost weight.


Corrosionpedia Explains Pitting Factor

One tool used to determine a metal's pitting factor is a pit gauge that maps the entire surface area and requires a skilled technician to operate, interpret and maintain. Other tools used are the machinist's depth gauges, dial indicator pit gauges and micrometer barrels. When the pit lengths are determined, it is the work of the inspectors to calculate the pitting factor from the available data. The inspectors then present their findings and control of the wear.

The effects on pitting corrosion resistance with nitrogen and molybdenum alloying have seen an improved passivated metal. The alloying helps to repair the passive layer whenever pitting attacks. This helps to stop the nucleation of the pit by preventing the aggressive anions like the chlorides from reaching the surface. The oxide-diffusion layer interface is the point where the anion prevails for the growth of the oxide. The pits have increased amounts of alloying element ions at the initiation of the attack. Nitrogen enhances the effects of molybdenum, which in turn influences its concentrations at the surface. This is explained by the ammonium ion production that increases the pH. Nitrogen increases iron dissolution while chromium dissolution decreases.


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