When we wanna talk about localized corrision, the first type of this detrimental phenomenon that comes to mind is “the pitting corrosion”. All inspectors who have worked in refineries have encountered localized pitting corrosion in stainless steel materials. A common type of corrosion that will occur on the surface of austenitic stainless steels due to the presence of chloride ions in the aqueous phase. But the important issue is to investigate and interprete this type of corrosion in carbon steel material. The type of pitting corrosion in carbon steel material is typically different from the pitting corrosion that occurs in stainless steel material in terms of morphology. In carbon steel material, the pits usually have a larger size and can expand from the small pit to larger cavities by joining each other. Investigating the cause of pitting corrosion in carbon steel material is very important, because sometimes corrosion experts only rely on reporting a uniform corrosion rate. For example, for the analysis of corrosion coupons that are replaced periodically in refineries, the operators usually report the uniform corrosion rate and pictures of the coupon after retrieving and after washing and weighting. So, if there are some pits on the surface of the coupon, it seems that it is necessary to further examine the coupons in the laboratory by the aid of a microscope. Even the surface inside the cavities can be further investigated with the help of elemental analysis by EDAX in order to conduct a root cause failure analysis. In research works, coupons at the end of the experiment are usually mounted and cutted from the pits location so that the shape of the hole and its distribution can be better investigated. Of course, doing this work in industrial environments is not an easy task, but by knowing the type of pits and measuring the pitting growth rate as a very dangerous type of corrosion, better analyzes of the condition of the equipment and pipelines can be provided. Hereafter, i am going to repost valuable data regarding different types of pitting that we may experience in our industry. You can visit my #researchgate page for some research papers regarding failure analysis in has refineries, via the following link: https://lnkd.in/eJbvFg5Q
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Corrosion Engineer
9moThank you for your informative post! It's very useful!