Corrosion damage caused by unreasonable structure
Thread Content
In the catalytic cracking unit of a large refinery, there are 64 kilometers of aluminum pipelines; in suitable locations, these aluminum pipes are grouped together and fixed inside channel steel, with the flanges of the channel steel facing upward. During testing, many of the aluminum tubes could no longer withstand pressure. Inspection revealed numerous erosion pits, some of which were perforated. Commentary: Using channel steel to support aluminum pipes is a common design approach. But here, the potential corrosive effects of such a design on aluminum tubes are overlooked. Channel steel with the flanges facing upward tends to collect water, as well as various types of trash and dirt. It is expected that aluminum pipes immersed in such wastewater containing various corrosive substances will suffer severe corrosion and perforation. Therefore, if channel steel supports are to be used, measures should be taken to prevent water accumulation, and installing drainage holes is a simple and effective method. Make sure the size and number of drainage holes are sufficient. To ensure smooth drainage and prevent blockages. Additionally, care must be taken during construction to prevent the aluminum tubes from being contaminated. Preventing liquid stagnation is an important principle in structural design. Because the accumulation of fluid leads to an intensification of corrosive conditions in the local area. Therefore, the inside of the container and piping systems should be streamlined and slightly inclined downstream and toward the outlet to facilitate liquid flow and discharge; a drain valve should be installed in the recessed sections.
I’ve learned that combining design, construction, and operation is the best way to maximize the protection of equipment and pipelines.
I think what you mentioned is one aspect; another factor to consider is electrochemical corrosion. Aluminum is more reactive than iron, so it will sacrifice itself first. In long-distance pipelines, reactive metals are used as sacrificial materials
Regarding the corrosion inspection of underground pipelines, there are currently issues such as inadequate supervision and a lack of appropriate methods. There is also insufficient attention paid to the inspection and supervision of the construction quality of underground pipelines; this often leads to stress being applied to them, and they lack protection due to being covered with construction sand. They might even be forgotten after being buried, and regular inspections fail to detect such situations
We know that aluminum is a reactive metal, and its electrode potential is lower than that of iron when there is no passivation film. In dry air, a dense oxide film about 50 angstroms thick forms immediately on the surface of aluminum, preventing further oxidation and allowing it to resist water ； Additionally, aluminum is amphoteric, meaning it is soluble in strong bases as well as in dilute acids. Therefore, in this case, if the appropriate measures are taken, electrochemical corrosion will not occur since the pipeline does not come into contact with water.