Pitting corrosion of stainless steel

Are you interested in pitting corrosion of stainless steels, from the company — supplier Alekhlas? Here you will find the necessary information on the topic.

The mechanism of the phenomenon

Pitting corrosion or pitting is a form of localized corrosion that produces effects on the surface of the steel in the form of spots or pits. Such corrosion can occur in stainless steels in neutral or acid solutions containing halides, above all chlorides (Cl-), which are very abundant in sea water.

Pitting corrosion attacks most often occur at points where the passive layer might be weakened, for example, slag inclusions, a damaged surface or defects in the passive layer. As soon as the attack begins, the penetration into the material can be carried out in the shortest time.

The problem with pitting corrosion attacks depend primarily on the chloride content, pH value (acidity) and temperature. If pitting has occurred, and if the environment it is not too corrosive for steel, the spontaneous recovery of the passive layer can occur in the presence of oxygen.

The content of chloride is often referred to as ppm (parts per million = 0,0001%). Some typical values of Cl:

Fresh water: 0−200 ppm (0−0,02 wt.%)

Brackish water: normally up to 15,000 ppm (1.5% wt.)

Seawater: normally 15 000−21 000 M. D. (1,5−2,1% wt.)

Natural seawater is more aggressive than would be expected from its content in chloride. The reason for that what will happen biological activity. Therefore, chlorination as a biocide, is often used to prevent the growth of microorganisms in sea water.

Supplier — the company Alekhlas — offers to purchase assortimente metal, made of different grades of stainless steels. Products can be purchased at a price formed on the basis of European and world standards. Possible, wholesale and retail, for regular customers a flexible system of discounts.

Ways of preventing pitting corrosion

If adding chlorine of 0.5−2 ppm occur occasionally (e.g. 2 x 30 minutes / 24 hours), the risk of pitting corrosion can be reduced. Intermittent chlorination is fully sufficient to prevent the growth of microorganisms. However, chlorine can cause increased risk of pitting corrosion due to oxidizing ability. The use of continuous chlorination increases this risk, so it is preferable to intermittent chlorination.

Several alloying elements have a positive effect on the material’s resistance to pitting:

Chromium (Cr) +

Molybdenum (Mo) +++

Nitrogen (N) +++

One way to assess the resistance of stainless steels to pitting corrosion is the equivalent resistance that can be calculated from the chemical composition of steel. The higher the value, the better the resistance.

There are several different methods of testing the resistance of steel to pitting.

Often used to determine the critical pitting temperature. This is one of the most difficult tests for the pitting-corrosion of stainless steel because of the acid solution in combination with chlorides and oxidizing capacity.

Supplier — the company Avecho offers various types of stainless steel domestic and foreign production. Products are offered at affordable prices from the manufacturer. Supplier guaranteed timely delivery at any address specified by the consumer.