Corrosion Mechanisms in Stainless steel pipe

The time of issue:2014-6-3 11:43:41       Author:

Compared to welded steel pipe, stainless steel pipe are more useful for corrosion resistant and can work satisfactorily in most environments. In general, the constituent elements of stainless steel pipe can be affected by the limit of corrosion resistance, that is, each grade of stainless steel pipe has different response when exposed to a corrosive environment. Therefore, when selecting the proper grade of stainless steel for a given application, we should be careful.

Pitting corrosion, which is localized form of corrosion, may be caused when exposing the stainless steel pipe to specific environments, most notably those containing chlorides. In the most cases of structural applications, the extent of pitting is superficial and the reduction in section of a component is negligible. But, architectural features can be stained by corrosion products. We should adopt a less tolerant view of pitting for services, for example, ducts, piping and containment structures.

The extremely low availability of oxygen of the welded steel pipe can lead to crevice corrosion which is a localized form of attack. The crevice corrosion may be only caused when a build-up of chlorides can occur. Whether the crevice corrosion is serious or not depends on the geometry of the crevice, that is, the crevice is narrower and deeper, and then the corrosion will be more severe. Crevices usually occur when the stainless steel pipe is under the environment of nuts and washers or around the thread of a screw or shank of a bolt. In addition, crevices can also occur in welds which fail to penetrate and under deposits on the steel surface.

The last kind is bimetallic corrosion which is also called as galvanic corrosion. That those dissimilar metals are in contact in a common electrolyte may lead to the bimetallic corrosion. What is more, the relative areas of the metals in contact, as well as the temperature and the composition of the electrolyte, will be depended on the rate of corrosion. Commonly, the rate of attack can be affected by the area of the cathode in relation to that of the anode. The previous experience in similar sites can be useful when the conductivity of the electrolyte is low. However, it is difficult to predict these effects.

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