Requirements for the Cleanliness of Air Compressor Piping

The Basic Objectives of Cleanliness

The key to maintaining the cleanliness of air compressor piping is minimizing the impact of internal residues on the compressed‑air system. The piping should be free of visibly detectable weld spatter, rust, sand, machining debris, oil contamination, fragments of sealing materials, and standing water. For systems in continuous operation or those with stringent air‑quality requirements, additional attention should be paid to controlling particulate matter, oil mist, and moisture.

Major Pollutants and Control Requirements

• Solid particles:The inner walls of the piping shall be free of loose scale, metal chips, sand particles, and dust to prevent their ingress into valves, cylinders, instruments, and gas‑using equipment.
• Oil Stain:The inner surface of the pipeline shall be free of any visible oil film or oil droplets to prevent oil contamination of the compressed air and to avoid adverse effects on downstream processing equipment.
• Moisture:After installation and purging, accumulated water should be minimized, and during operation, condensate should be controlled using drainage systems and drying equipment.
• Construction residues:Sealant, scraps of PTFE tape, welding slag, and burrs on pipe ends shall be thoroughly removed to prevent blockages or abrasion.

Cleaning Requirements During the Installation Phase

During pipe fabrication and installation, pipe ends shall be kept sealed to prevent the ingress of soil, rainwater, and foreign debris. After cutting, beveling, and welding, all spatter, scale, and burrs must be removed. When storing pipes, avoid open‑air stacking to prevent internal moisture absorption and contamination. Until installation is complete, pipes should not be left open for extended periods; where necessary, temporary plugs or end caps may be used.

Purging and Flushing Requirements

Compressed air pipelines that have been newly installed or overhauled typically require purging. Purging shall be carried out in sections using compressed air or a method approved by the project, until the outlet airflow is free of visible particles and contaminants. During purging, avoid sensitive instruments, control valves, and end‑use pneumatic equipment; if necessary, remove or isolate the relevant components beforehand. Upon completion of purging, promptly restore the system and perform leak testing.

Acceptance Inspection Method

• Visual inspection:Inspect the pipe openings, low-point drain outlets, and the upstream side of the filter for visible rust, oil contamination, standing water, and foreign matter.
• White cloth or filter paper test:Place a clean white cloth or filter paper at the purge outlet and inspect for any visible particles, oil stains, or water marks.
• Filter Inspection:Monitor the differential pressure and drain condition of the pre‑filter to determine whether significant impurities remain in the pipeline.
• Project testing requirements:For systems with specific requirements for gas quality, particle, oil‑content, and moisture‑content tests may be conducted in accordance with the technical documentation.

Moisture, Oil, and Filtration Control

Pipeline cleanliness depends not only on the construction phase but also on the air compressor, downstream processing equipment, and operational management. Appropriate filters, drying units, and automatic drain devices should be selected to meet air‑use requirements. Filters should be installed in locations that facilitate maintenance and replaced based on differential pressure or service life. Drain points should be provided at low points in the piping system to enable the removal of condensate and accumulated deposits.

Operation and Maintenance Requirements

• Regularly inspect the low-point drain valves and automatic drains to ensure proper drainage.
• Regularly check the filter differential pressure to prevent clogging or failure of the filter element.
• Prior to recommissioning after maintenance, local cleaning and purging shall be performed.
• When rust, leaks, increased water accumulation, or abnormal pressure drops are detected, the source of contamination should be investigated.
• For critical gas‑using points, a system of regular inspections and record‑keeping may be established.

Safety Precautions

Before conducting pipeline inspection, purging, or cleaning, ensure that the system has been depressurized and that energy sources have been isolated. Discharge outlets should be positioned away from personnel and equipment to prevent high‑velocity gas streams from entraining contaminants and causing injury. When using chemical cleaning agents, verify their compatibility with the pipe materials, seals, and subsequent gas‑using processes, and dispose of waste liquids in accordance with applicable regulations.