How to deal with limescale buildup on seamless steel pipes for fire protection service

Seamless steel pipes for fire protection are familiar to all. They are long steel products with hollow cross-sections and seamless peripheries. Resistant to weakly corrosive media such as air, steam and water, as well as chemical corrosive media including acids, alkalis and salts, they are also known as stainless acid-resistant steel pipes.

As hollow round long steel tubes, fire-fighting seamless steel pipes are widely applied in industrial pipelines and mechanical structural components for petroleum, chemical, medical, food, light industry, mechanical instrumentation and other industries. Moreover, under equal bending and torsional strength, they feature lighter weight, so they are also extensively used to manufacture mechanical parts and engineering structures.

However, oxide scale will form on fire-fighting seamless steel pipes after long-term service. Many people lack sufficient knowledge and operational skills to handle this issue. To facilitate your operation, the common treatment methods are introduced as follows:

1. Flushing

   Prior to pickling, flush the fire-fighting seamless steel pipes thoroughly to remove sludge, scale and other impurities inside heat exchangers. This improves pickling efficiency and reduces acid consumption.

2. Pickling

   Flood the pipes with acid solution for static soaking for 2 hours, followed by continuous dynamic circulation cleaning for 3 to 4 hours. Alternate forward and reverse circulation every 0.5 hours during the process. After pickling, the acid solution can be reused if its pH value is higher than 2; otherwise, it shall be diluted, neutralized and drained off.

3. Alkaline Washing

   After pickling, prepare alkaline solution with sodium hydroxide (NaOH), trisodium phosphate (Na₃PO₄) and softened water in a certain proportion, then carry out dynamic circulating alkaline washing to achieve acid-base neutralization and prevent further corrosion of the pipes.

4. Water Rinsing

   After alkaline washing, repeatedly rinse the pipes with clean softened water for 0.5 hours to completely flush out residual substances inside the tubes.

5. Record Keeping

   Accurately record the duration of each step during cleaning and inspect the cleaning effect.

For daily service of fire-fighting seamless steel pipes, proper maintenance knowledge is essential. Regular maintenance guarantees stable operation. When limescale accumulates, the above cleaning procedures can be adopted to clean the pipes.