How to Prevent Flash Rusting in Pipelines?

Since the beginning of the 21st century, China's economy has maintained robust growth, driving an increasing demand for various fuels, natural gas, and petroleum products. Compared to road and water transportation, pipeline transmission offers advantages such as high efficiency, cost-effectiveness, safety, and continuous operation, making it the preferred method for long-distance transportation.

To ensure the economic viability and safety of pipeline construction and operation, the fundamental requirements and development trends for pipeline steel include high strength, high toughness, large deformation capacity, thick-walled design, high corrosion resistance, and excellent weldability. Pre-welding technology currently represents one of the most advanced techniques in the production of large-diameter, thick-walled pipelines. However, due to constraints such as operational and welding processes, rust spots may appear at welds after applying anti-corrosion coatings, compromising weld quality and thereby reducing pipeline integrity.

When water-based coatings are applied to pipeline welds and allowed to dry naturally, water remains on the metal substrate for extended periods, causing rapid rust formation at welds—a phenomenon termed “flash rust.” Flash rust is an electrochemical phenomenon related to the dissolution and precipitation of iron compounds. Since water-based coatings are conductive, they form charge migration pathways between areas with potential differences. Under the combined action of water and oxygen, corrosion occurs.

Measures to prevent flash rust on welds:

1.  Coating thickness: Thicker coatings at welds increase flash rust risk, as excess thickness hinders moisture evaporation.

2.  Accelerated drying: Higher temperatures and lower humidity effectively prevent flash rust formation.

3. Coating pH: Higher pH values reduce flash rust susceptibility; adjusting pH to approximately 9.5 is optimal.

4. Resin systems: Self-drying systems like styrene-acrylic or 100% acrylic emulsions are most prone to flash rust, whereas water-soluble acrylic and polyester resin systems exhibit lower susceptibility.

5. Use of flash rust inhibitors: Properly formulated flash rust inhibitors can effectively prevent flash rust formation.

In the coatings industry, preventing flash rust in water-based coatings is not inherently challenging. However, during actual application, various factors can affect the efficacy of flash rust inhibitors. For instance, standard inhibitors may struggle to suppress flash rust at weld seams. Selecting targeted, suitable flash rust inhibtors is crucial. This approach not only effectively resolves flash rust issues but also enhances the long-term water resistance of the paint film and improves internal corrosion protection performance.