Importance of chemical cleaning in hydraulic piping?

Before commissioning hydraulic piping, chemical cleaning is used to remove mill scale, rust, and welding slag from the interior surfaces. This prevents contamination, which can damage valves, pumps, and cylinders in the first few hours of operation. Even if the pipe is well-made, it will never be completely clean inside. The mechanical flushing can't always remove the oxide or scale layers that are tightly adhered. This means a system may pass visual inspection but still be at risk of premature failure. The chemical cleaning fills in that gap. Skipping this step is one of the most costly and common mistakes made when commissioning hydraulic systems.

Why is it important to clean the piping before starting up?

Hydraulic systems are operated at very tight clearances. The internal components of a piston pump may be run to tolerances as fine as a few microns for a servo valve's spool. The components are prone to wear down if there is any hard matter in the fluid. This could be mill scale from a pipe, rust from storage, or weld spatter.

It's not always an immediate failure. It's more likely to be a gradual degradation, with seal surfaces losing their finish or worn-out pump barrels. When symptoms like erratic pressure or sluggish actuator responses, or increasing noise levels, appear, the damage has already been done. This is addressed by chemical cleaning at the source before fluids circulate through precision components.

What is inside a "clean," brand-new pipe?

Even piping that is stored and installed properly typically contains:

• Mill scale is an oxide layer that forms during hot rolling steel. It is loosely bound and susceptible to flaking when subjected to flow or vibration.
• Rust—from storage, transport, or humidity exposure before installation
• Welding spatter and slag—residues of field welding pipe joints
• Preservative coatings and cutting oils—applied to the metal during fabrication in order to prevent corrosion.
• Construction debris—dust, sand, or foreign materials introduced during installation

These are not visible after the piping has been assembled and closed, so they do not need to be cleaned.

What is the difference between chemical cleaning and mechanical flushing?

Many commissioning teams use hydraulic fluid, or low-viscosity oil that is circulated at high speed to transport loose particles to filters. Flushing is important and necessary but has limitations. It only removes contaminants that are loose, not those chemically attached to the pipe walls.

Even under turbulent flushing, mill scale can adhere to the system. It will then gradually release over several weeks or months as the system vibrates. This is why systems that "passed" flushing cleanliness checks can still develop contamination-related failures well after startup.

The chemical cleaning process uses alkaline or acid solutions in combination with mechanical circulation to dissolve these layers and separate them before the pipe is connected to sensitive components or before it's final connection.

Chemical cleaning sequences

1. Degreasing—removes organic residues and cutting oils using alkaline or solvent-based solutions
2. Acid pickling—A dilute acid solution dissolves mill scale and corrosion (usually hydrochloric acid or citric for stainless steel systems).
3. Rinsing—thorough flushing of the cleaning chemicals with water or a compatible fluid.
4. For stainless steel pipes, passivation restores the protective layer of chromium oxide.
5. Before hydraulic fluid is added, neutralization and drying ensures that no reactive residues remain.

If you skip any of the steps, residual chemical activity can attack seals and fluid additives in the future.

The consequences of not using chemical cleaners

Costs of contaminated piping are rarely apparent on the first day, which is why this step can be skipped due to schedule pressure. Real costs are revealed later and tend to be more than the time savings.

Component wear accelerates. Pumps and valves circulating abrasive particles cause sliding surfaces to wear in three directions, reducing component life below the rated hours.

Valve sticking, erratic control. The fine-scale particles can lodge in the servo valve and proportional clearances without being caught by the standard filter. This causes intermittent sticking, which is difficult to diagnose.

Premature seal failure. Particulates that are hard embed themselves in the dynamic seal surfaces and create leak paths, which widen with time. This failure mode is often misattributed to contamination rather than seal material selection.

Filter loading can cause unplanned downtime. Filter clogging can occur in a very short time with systems that have not been cleaned. The fluid is slowly carrying loose scale into the filter stage.

Warranty and reliability disputes. When component manufacturers investigate failures that occur early, contamination due to uncleaned piping can be a common root cause. This can complicate warranty claims when commissioning records do not show a documented cleansing process.

Chemical cleaning is not negotiable.

Chemical cleaning is not required for every hydraulic system, but in certain cases it is essential.

• Long pipe runs, with multiple field weldings where the slag and scaling accumulation is greatest
• High-pressure systems are used in environments where clearances between components and contamination are the tightest.
• The servo and proportional valves are more sensitive to contamination by fine particles than standard directional valves
• Systems using specialty fluids or fire-resistant fluids where the filtration may behave differently and particulate tolerance may be lower
• Reusing cleaned and commissioned pipes or new construction is preferable to major piping replacements.

Chemical cleaning: Best practices

To get the most out of chemical cleaning, you need to be disciplined in the process and not just run the chemicals down the line.

• Use particle counting or patch tests to test cleanliness before and after visual inspection.
• Choose the right cleaning solution for the material of the pipe. Carbon steel, stainless steel, and galvanized pipes all require different alkaline or acid formulations.
• Keep sensitive components such as pumps and valves away from the circuit until you have verified that your cleanliness target has been met.
• Since residual cleaning chemicals may react with fluid additives or even attack elastomeric sealings, it is important to fully neutralize and thoroughly rinse the hydraulic fluid before adding any fluid.
• Document the cleaning results and process for both commissioning records as well as any future warranty or failure investigations.

It's easy to ignore chemical cleaning when commissioning deadlines are tight, because it doesn't create immediate and visible problems. Hydraulic systems are not forgiving when it comes to internal contamination, especially within the tolerances that they work with. The piping is one of the biggest—and most overlooked sources -- of this contamination. It is more cost-effective to invest in a chemical cleaning program that is verified by real cleanliness tests rather than visual checks.

1. Does chemical cleaning need to be done if the pipes look clean?

Yes. Even when there are light oil or preservation coatings, mill scale, rust, and welding residues can be difficult to see. Visual inspections cannot confirm that there is no chemically bonded contamination, which chemical cleaning can remove.

2. What is the difference between hydraulic flushing and chemical cleaning?

Flushing is a method of removing loose particles by circulating fluid at high speed. It is usually done after chemical cleaning. Chemical cleaning is the use of acid or alkaline solution to dissolve contaminants that are chemically bonded on the pipe walls and which flushing cannot remove.

3. Can stainless steel hydraulic pipes be cleaned without chemicals?

No. Chemical cleaning is important, but not less so, for stainless steel systems.

4. How can the cleanliness of a chemically cleaned surface be verified?

Standard methods include particle counting and patch tests against ISO cleanliness codes. This gives a quantitative result, rather than relying solely on visual inspection, which is unable to detect fine particulate contaminants.

5. How much does chemical cleaning impact the timeline for commissioning?

It adds time upfront, typically measured in days depending on system size and pipe run length, but this is generally far shorter than the downtime caused by contamination-related component failures discovered after startup.