Industrial Metal Pipe Cleaning and Purging
Aug 12, 2025
Pipe Cleaning and Purging
According to the "Code for Construction and Acceptance of Industrial Metal Pipeline Engineering" (GB50235), pipelines should be purged or cleaned (referred to as purging) after passing the pressure test. The purging method should be determined based on the pipeline's operating requirements, the medium being transported, and the degree of contamination on the pipeline's internal surface. Purging methods include water cleaning, chemical cleaning, oil cleaning, air purging, and steam purging. Liquid or gas pipelines with a nominal diameter greater than or equal to 600mm should be cleaned manually; liquid pipelines with a nominal diameter less than 600mm should be flushed with water; gas pipelines with a nominal diameter less than 600mm should be purged with air; steam pipelines should be purged with steam; steam purging should not be used on non-thermal pipelines.
1. Water Cleaning
Water cleaning refers to water flushing. Pipeline flushing should be done with clean water. When flushing austenitic stainless steel pipes, the chloride ion content in the water must not exceed 25 parts per million. Flushing should be conducted at maximum flow rate, with a velocity of no less than 1.5 m/s. Discharge water should be directed to a reliable drainage well or trench, with the cross-sectional area of the discharge pipe no less than 75% of the cross-sectional area of the pipe being flushed. Negative pressure should not be generated during drainage. All drainage branches of the pipeline should be flushed. Water flushing should be continuous, with the color and transparency of the water at the outlet visually consistent with the water at the inlet considered acceptable. When the pipeline is temporarily out of service after a qualified water flush, it should be promptly air-dried.
II. Chemical Cleaning
During chemical cleaning, pipelines must be isolated from unrelated equipment. The chemical cleaning solution must be formulated and proven effective and reliable in production facilities. Operators should wear specialized protective clothing and, depending on the hazards posed by the different cleaning solutions, goggles, gas masks, and other protective gear. Pipelines that have passed chemical cleaning and cannot be immediately put back into operation should be sealed or nitrogen-filled for protection. The treatment and discharge of wastewater after chemical cleaning must comply with environmental regulations. Acid cleaning and alkaline cleaning of pipelines fall under the category of chemical cleaning.
III. Oil Cleaning
Lubricating, sealing, and control oil pipelines should be oil cleaned after the machinery and pipelines have passed the acid cleaning process and before system commissioning. Oil cleaning should be performed using an oil circulation system. During the circulation process, the oil temperature should be repeatedly raised and lowered within the range of 40-70°C 2-3 times every 8 hours. Filter elements should be cleaned or replaced promptly. Unless otherwise specified in the design documents or by the manufacturer, pipelines should be inspected using a filter after oil cleaning. The acceptance criteria should be a 200-mesh filter for machinery speeds ≥ 6000 r/min, or a 100-mesh filter for machinery speeds < 6000 r/min. Visual inspection of the filter screen should ensure the absence of hard particles and sticky matter, with no more than 3 soft debris per cm². Oil cleaning should be performed using a qualified oil suitable for the machinery being cleaned. Effective protective measures should be implemented for pipelines that have passed the cleaning process. Before commissioning, certified working oil should be used. IV. Air Purging
Pipeline air purging should utilize the production facility's large compressor. Intermittent purging can also be performed using large containers within the facility to store air. The purging pressure must not exceed the pipeline's design pressure, and the flow rate should not be less than 20 m/s. When purging oil-sensitive pipelines, the air must be free of oil. During the air purging process, if the exhaust is visually clear of smoke and dust, a wooden target plate covered with white cloth or painted white should be placed at the exhaust port for inspection. A pass mark is considered acceptable if the target plate is free of rust, dust, moisture, or other debris within 5 minutes. 5. Steam Purging
When steam purging pipelines, temporary piping installed for steam purging should be installed in accordance with steam pipeline technical requirements, and the installation quality should meet regulatory requirements. Steam pipelines should be purged with a high flow rate of steam, with a flow rate of no less than 30 m/s. Before steam purging, the pipelines should be purged in a cycle of heating, cooling, and reheating. Purging should be carried out one pipeline at a time, rotating the pipelines. For steam pipelines leading to steam turbines or as specified in the design documents, the target should be inspected after steam purging. If not specified in the design documents, the quality should meet the following requirements: a mark on the target of less than 0.6 mm in diameter, a mark depth of less than 0.5 mm, a particle count of 1/cm², and a duration of 15 minutes (two passes are considered acceptable).
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