43. Why is it effective to swing the steel pipe or circulate the solution during pickling?

When performing acid pickling on steel pipes, three key observations emerge: First, oscillating the pipes or using steam to agitate the pickling solution significantly enhances the pickling rate compared to static placement. For instance, in a reciprocating pickling frame, swinging the pipes at 30 cycles per minute increases the pickling speed by approximately 70%. Alternatively, using hot air to stir the solution improves the pickling rate by about 20%. Second, the scouring action reduces hydrogen deposition on the pipe surface, decreasing hydrogen diffusion into the metal matrix. This minimizes acid embrittlement and maintains mechanical strength. Simultaneously, the scouring process removes steam bubbles, impurities, iron salts, and oxide scales, resulting in a cleaner pipe surface. Third, agitated solutions maintain uniform composition, extending the solution's service life.