Microbiologically Induced Corrosion

Water can enter into the pipelines in various ways, either at pre-commissioning phase (hydrotesting) or during commissioning and use. Even if the operating temperature is above the dew point, one must not forget that due to factors, such as but not limited to, existing of low points and temperature fluctuation and operation age of the line, water can be collected inside the pipe. It is also interesting to note that as long as water exists (even as water pockets) within the line, the likelihood of both electrochemical and electrochemical-microbial corrosion in the form of internal corrosion, manifested as pitting, will highly increase.

In addition, one has to know that there are two approaches towards microbial corrosion cases” study of the case as per system” and “study of the case as per material”l. In other words, if one knows under what conditions for instance carbon steel corrodes by microbes, it doesn’t matter if the system in which carbon steel has been used in, is a pipeline or a tank and whether if it is in a power plant or a gas refinery.

On the other hand, Hydrotesting (or alternatively, hydrostatic testing) is an industrial practice that is of frequent use in industry. The main characteristic of hydrotesting is that it is a “leak” and “strength” test. There are many factors that can be involved in making a system vulnerable to microbiologically influenced corrosion (MIC). Of the four principle corrosion mechanisms that can be expected to see, MIC is the mostprobable/ important one in a post-hydrotest failure. More ever, when pigging is done (intelligent pigging for instance) it is quite possible that it will increase the risk of MIC as well.