How can corrosion of stainless steel pipelines for process gas in petrochemical acidic water stripping units be prevented?
Thread Content
The image below shows the pipeline corrosion in a stainless-steel process gas unit for the acid water stripping of a petrochemical plant, where volatile components in the acid water (such as H₂S, NH₃, and CO₂) are transferred from the liquid phase to the gas phase. The pipe originally had a wall thickness of 8 millimeters, and after more than 3 years of use, its thickness decreased to around 4 millimeters. What protective methods can be used to avoid corrosion?
To address the corrosion issue in the process pipelines of acidic water stripping units, the following protective measures can be taken: 1. **Material upgrade** – Consider replacing the existing materials with more corrosion-resistant ones, such as **duplex stainless steel (2205/2507)** or **nickel-based alloys (such as Incoloy 825)**, to enhance resistance to H₂S, NH₃, CO₂, and chloride-induced stress corrosion. 2. **Process optimization** - Strictly control the operating parameters of the stripping tower (temperature, pressure, pH value) to prevent acidic gases from condensing and creating a wet corrosion environment. - Optimize the water injection or corrosion inhibitor injection process to reduce the concentration of corrosive substances. 3. **Coating/Lining Protection** A **corrosion-resistant alloy lining (such as titanium lining)** or a **polymer coating (such as PTFE)** is used on the inner wall of the pipeline to isolate corrosive agents. 4. **Structural design improvements** – Avoid low-flow areas to prevent water accumulation and solid deposition. - Optimize the pipeline layout by reducing U-turns and dead corners, thereby lowering the risk of localized corrosion. 5. **Monitoring and Maintenance** - Conduct regular **ultrasonic thickness testing** and corrosion probe monitoring to establish a corrosion rate database. - Implement **proactive replacement** of severely thinned pipe sections to prevent sudden leaks. 6. **Corrosion inhibitors**: Specialized corrosion inhibitors are selected based on the composition of the medium, and their continuous or intermittent injection is used to reduce the corrosion rate. It is recommended to prioritize **analysis of the causes of corrosion** (such as medium composition, temperature, flow rate, etc.), select a comprehensive protection strategy based on economic considerations, and strengthen daily process monitoring and maintenance. .