How can one prevent the occurrence of excessive corrosion after the acid washing of stainless steel

To prevent excessive corrosion after the acid washing of stainless steel pipes, the following aspects can be considered:

Selecting the appropriate acid washing agent

Choose the acid based on the material: Different models of stainless steel pipes have different material compositions, so an appropriate acid washing agent needs to be selected. For example, 304 stainless steel can use a mixed acid washing agent composed of nitric acid and hydrofluoric acid, while for 316 stainless steel containing molybdenum, the concentration of hydrofluoric acid in the acid washing agent should be appropriately adjusted to ensure the acid washing effect and prevent excessive corrosion.

Controlling the concentration of the acid washing agent: Strictly control the concentration of each component in the acid washing agent according to the process requirements. For example, if the nitric acid concentration is too high, it will accelerate the corrosion rate and easily lead to excessive corrosion. Generally, the nitric acid concentration should be controlled at 10% - 20%, and the concentration of hydrofluoric acid should be controlled at 1% - 3% for better acid washing effect and to prevent excessive corrosion.

Precisely controlling the acid washing process parameters

Controlling the acid washing temperature: Temperature has a significant impact on the acid washing speed, so it should be controlled reasonably according to the composition of the acid washing agent and the material of the stainless steel pipe. For example, when using a mixed acid washing agent of nitric acid and hydrofluoric acid, the acid washing temperature is generally controlled at 40 - 60℃. If the temperature is too high, the acid washing reaction will be too intense, increasing the risk of excessive corrosion.

Strictly controlling the acid washing time: The acid washing time should be determined based on the thickness of the oxide scale on the surface of the stainless steel pipe and its material. Generally, for general oxide scale stainless steel pipes, the acid washing time is controlled at 15 - 30 minutes. If the time is too long, the metal will be overly dissolved, thereby causing excessive corrosion.

Strengthening monitoring during the acid washing process

Real-time monitoring of acid liquid components: During the acid washing process, use chemical analysis instruments to regularly detect the changes in the concentration of each component in the acid washing agent and replenish the consumed acid liquid components in time to ensure that the concentration of the acid washing agent is within a reasonable range.

Observing the acid washing reaction: Assign a dedicated person to monitor the reaction of the stainless steel pipe during the acid washing process, such as the speed and quantity of bubbles produced. If the reaction is too intense, immediately remove the stainless steel pipe from the acid liquid and take corresponding measures to adjust the acid washing process parameters.

Doing a good job in the treatment after acid washing

Timely cleaning: After acid washing, immediately use a large amount of clean water to rinse the stainless steel pipe to thoroughly clean the residual acid on the surface to prevent the residual acid from continuing to react with the metal and cause excessive corrosion.

Carrying out passivation treatment: The cleaned stainless steel pipe should be promptly subjected to passivation treatment to form a dense passivation film on its surface, enhancing corrosion resistance and effectively preventing further corrosion of the stainless steel pipe surface by external factors, avoiding the occurrence of excessive corrosion.