Flanges are crucial pipeline components, and many people tend to neglect cleaning them once they are installed, believing that it serves no purpose. However, post-installation cleaning of flanges is of utmost importance.

When flanges rust or become dirty, they are prone to damage, leading to pipe leaks. Therefore, it is essential to prioritize flange cleaning after installation. Only through effective cleaning can the lifespan of flanges be extended, and the occurrence of pipe leaks be prevented.

Carbon steel flanges may encounter cleaning issues after the process of heat treatment and tempering. For instance, improper stacking of carbon steel flanges or the wrong selection of alkaline quenching and quenching oil can result in surface rust. In such cases, the flanges are susceptible to damage.

Therefore, it is crucial to pay attention to these aspects during the cleaning process. The specific cleaning techniques are as follows:

1. Alkaline Cleaning

The residual heat from quenching carbon steel flanges can cause surface blackening. However, there are visible light-colored areas on the outer ring, including red and light blue regions, which enhance flange rigidity. To facilitate the threading process, a phosphate coating is applied to metal wires and round bars without rinsing, followed by direct heat treatment.

By doing so, the preparatory work for alkaline cleaning is essentially completed. Subsequently, the flanges are cooled in quenching oil and cleaned with alkaline detergent. The flanges themselves are tempered at a temperature of 550 degrees Celsius. During this process, the appearance of red areas on the screws is caused by alkaline corrosion of carbon steel, and it is possible to detect some calcium compounds and chlorides.

2. Dirt Flushing

After quenching carbon steel flanges, they are cleaned with a silicate-based detergent. Solid substances may appear on the surface, which can be analyzed using an infrared spectrometer. The results usually indicate the presence of iron oxide and inorganic silicates.

3. Acid Pickling and Rust Removal

Black streaks commonly occur on carbon steel flanges, which are also a form of rust. During removal, it is important to note that even after careful cleaning before heat treatment, these streaks may still be present post-tempering. Therefore, strict adherence to standards is necessary during this step.

Failure to pay attention to these details during the cleaning process can make it challenging to remove rust from the surface of carbon steel flanges and can potentially damage the flange structure. The analysis of black streaks using an infrared spectrometer typically reveals higher concentrations of calcium and sulfur.

By conducting a strong folding test with filter paper soaked in isopropanol with a small amount of acetic acid, the black spots remain on the paper, allowing for the separation of black substances from the carbon steel flanges. Analysis of the filter paper using an infrared spectrometer confirms that sulfur, calcium, manganese, iron, and chromium are the primary elements. The choice of acid pickling method depends on these key elements, as different methods yield different results.

This is some essential knowledge about cleaning carbon steel flanges. Did you find it informative?