The first stage of chemical cleaning removes oils, greases, and manufacturing residues from the internal pipe surfaces. Alkaline degreasing solutions are circulated through the system at controlled temperatures and flow rates, preparing the pipework for the pickling stage.

Acid-based pickling dissolves rust, mill scale, and oxide deposits from the internal surfaces of carbon steel pipework. The pickling solution is circulated under controlled conditions to ensure complete coverage, particularly in complex circuits and confined sections.

Following pickling, a neutralising solution is circulated to raise the pH of the system and halt the acid reaction. This prevents flash rusting and prepares the pipe surfaces for passivation.

A passivation solution — typically sodium nitrite-based — is applied to form a stable, corrosion-resistant film on the internal pipe surfaces. This protective layer significantly extends the time before re-contamination can occur during the period between cleaning and commissioning.

The system is purged with dry compressed air or nitrogen to remove residual moisture before hydraulic oil flushing begins. Thorough drying is critical to prevent water contamination of the hydraulic fluid and corrosion of sensitive components.

High-velocity oil flushing is performed using low-viscosity hydraulic fluid to generate turbulent flow — dislodging and carrying remaining particulates through the filtration system. Flushing continues until the required cleanliness level is achieved and confirmed by particle counting.

HydraPro targets and certifies cleanliness to NAS 3 (equivalent to ISO 4406 – 14/12/10) for critical hydraulic systems including rolling mills, precision machine tools, and sensitive offshore equipment. Particle count verification is performed using online counters, and full documentation is provided with each completed job.