The purpose of protective caps is to prevent corrosion on bolted connections or to slow down such damaging processes. Since there are a large number of different products on the market, the selection of a suitable protective cap is of crucial importance.
Not all protective caps are the same.
They may appear similar at a cursory glance but these protective systems can vary greatly. What goes on inside a cap and its structural composition play a great role here. The choice of the wrong protective cap not only does little to counteract corrosion processes but can in the worse cases even accelerate such processes. Experts divide corrosion into different categories. A particularly aggressive type of corrosion is the so-called crevice corrosion which occurs in areas where two surfaces are in close contact with each other and where humidity can accumulate. The crevice formed between the two surfaces has a very small volume and the process of crevice corrosion is triggered in such a crevice even at extremely low levels of corrosion. An acidic, low-oxygen medium which is many times more aggressive than the processes in surface corrosion is formed very quickly in the crevice. Unlike other types of corrosion, crevice corrosion is also triggered at lower temperatures and in a less acidic medium. The purpose of the following example, in which the effect of crevice corrosion was not taken into account, is to show the consequences of choosing an unsuitable protective cap.