47. What is the purpose of cleaning?

After acid washing, steel pipes must be immediately immersed in flowing cold or hot water to remove residual acids, iron salts, and carbon particles that hinder hot-dip galvanizing. Tests show that sulfuric acid solution leaves 7g/m² of iron salts, while hydrochloric acid solution reduces this to 2.3g/m². Post-acid washing cleaning can further decrease iron salt content to 0.5-1g/m². Hot water cleaning is particularly effective, as it also removes hydrogen from the pipe's core. This demonstrates that proper cleaning is a critical step in ensuring the quality of hot-dip galvanized steel pipes.