Flushing and Pickling Operations: Cleaning and Protection Strategies in Hydraulic Systems

Flushing and Pickling Operations: Cleaning and Protection Strategies in Hydraulic Systems

Flushing and Pickling Operations: Cleaning and Protection Strategies in Hydraulic Systems

Flushing and Pickling operations are indispensable applications for the healthy operation of modern hydraulic systems. Implementation of these processes with the correct parameters, especially in systems that require initial commissioning, large-scale revisions or high precision; It prevents breakdowns, increases energy efficiency and reduces operating costs.

The level of cleanliness within the system is critical for the long-lasting, efficient and safe operation of hydraulic systems. In this context, flushing and pickling (chemical cleaning and passivation) processes stand out as processes that directly affect the performance and life of the system, especially in new system commissionings, major maintenance processes or contaminated systems.

What is Flushing?

Flushing is the process of cleaning with high-flow, low-viscosity oil to remove particles, metal shavings, production residues, aged oil, sediment and other contaminants from a hydraulic system. In this process, the system is operated at a flow rate well above normal operating conditions, resulting in turbulent flow instead of laminar flow. Thus, the particles accumulated in the line are removed and made filterable.

Flushing Process Stages

1. Preparation: A flushing unit suitable for the cleaning system is prepared. Generally, special flushing oils with low viscosity are used.
2. Connection: The flushing unit is connected to the system line to be cleaned. The return line is routed so that it is filtered.
3. Heating: The oil is heated to a certain temperature (e.g. 50–60°C) so as not to damage the system materials.
4. High Flow Circulation: Turbulence is created by circulating with high flow in the system. This allows the removal of deposits within the line.
5. Filtration and Monitoring: The filter in the return line is constantly monitored. According to ISO 4406 coding, the process continues until the desired cleaning class is achieved.

Flushing Success Criteria

• Cleanliness Class: Achieve the target cleanliness level set in accordance with ISO 4406:1999 (e.g. 18/16/13).
• Filter ΔP Value: The pressure difference on the filter should be fixed; if it continues to increase, it means that the system is still dirty.
• Analysis Report: The level of cleanliness should be documented with particle count reports.

Pickling (Chemical Cleaning and Passivation)

Pickling is a chemical cleaning process applied especially in steel and pipelines to remove chemical contaminants such as rust, oxide layer, welding residues and to passivate the surface. Reacted dirt on the inner surfaces is removed using acidic solutions in controlled concentrations that do not harm the system. Then, the re-oxidation of the surface is prevented by the passivation process.

Pickling Process Steps

1. Circuit Preparation: The line is insulated and a system suitable for the chemical is installed.
2. Pre-flush: Large particles are removed beforehand.
3. Chemical Circulation: The acidic solution is circulated in the system for a certain period of time.
4. Neutralization: Basic neutralizing liquid is applied to stop the effect of the chemical.
5. Passivation: Passivation solution is applied to protect against corrosion.
6. Final Rinse: The system is rinsed and dried with deionized water.

Differences Between Flushing and Pickling