Pipeline cleaning and purging

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Piping cleaning and purging: In accordance with the requirements of the \"Code for Construction and Acceptance of Industrial Metal Piping Projects\" (GB50235), after the piping has passed the pressure test, it should be purged or cleaned (referred to as purging and cleaning). The purging method should be determined based on the usage requirements of the pipeline, the medium being transported, and the degree of dirt on the inner surface of the pipeline. Methods of purging include water cleaning, chemical cleaning, oil cleaning, air purging, steam purging, etc. For liquid or gas pipelines with a nominal diameter of 600 mm or more, manual cleaning is recommended ； Liquid pipelines with a nominal diameter of less than 600 mm should be flushed with water ； Gas pipelines with a nominal diameter of less than 600 mm should be purged with air ； Steam pipes should be purged with steam ； Steam purging shall not be used for non-thermodynamic pipelines. I. Water cleaning: Water cleaning refers to rinsing with water. Clean water should be used for pipe flushing; when flushing austenitic stainless steel pipes, the chloride content in the water must not exceed 25 parts per million ； During flushing, the maximum flow rate should be used, with a flow velocity of not less than 1.5 m/s ； The discharged water should be directed into reliable drainage wells or ditches; the cross-sectional area of the discharge pipe must be no less than 75% of that of the pipe being flushed, and negative pressure must not be created during drainage ； All the drainage branches of the pipeline should be flushed ； The water flushing should be carried out continuously, and it is considered successful when the color and transparency of the water at the outlet are visually consistent with those of the water at the inlet ； When the pipeline has passed the water flushing test but is not yet in operation, it should be dried out promptly. II. Chemical cleaning: When pipes are subjected to chemical cleaning, they must be isolated from unrelated equipment ； The formula of the chemical cleaning solution must have been evaluated and used in production facilities, having proven to be effective and reliable through practical use ； During chemical cleaning, operators should wear special protective clothing, and depending on the hazards posed by different cleaning agents, they must also use protective equipment such as goggles and gas masks ； Pipes that have passed chemical cleaning but cannot be put into operation promptly should be sealed or protected with nitrogen ； The treatment and discharge of waste liquid after chemical cleaning must comply with environmental protection regulations. The acid cleaning and alkali cleaning of pipes both fall under the category of chemical cleaning. III. Oil cleaning: Lubrication, sealing, and the treatment of oil pipelines should be carried out after the machinery and pipelines have been properly pickled, and prior to the system’s trial operation ； Oil cleaning should be carried out through oil circulation; during this process, the oil temperature should be raised and lowered repeatedly 2–3 times every 8 hours within the range of 40–70°C, and the filter element should be cleaned or replaced promptly ； When there are no requirements specified in the design documents or by the manufacturer, filter inspection should be carried out after the pipes have been cleaned with oil. The acceptance criteria are as follows: when the mechanical speed is ≥ 6000 r/min, a filter with a mesh size of 200 mesh should be used; whereas when the mechanical speed is < 6000 r/min, a filter with a mesh size of 100 mesh should be used. Visually inspect the filter to ensure that there are no hard particles or sticky substances, and that there are no more than 3 soft debris particles per cm2 area ； Oil cleaning should use qualified oil suitable for the machinery to be cleaned; effective protective measures should be taken when cleaning pipes ； Working oil with a certificate of conformity should be used before trial operation. IV. Air Purging: Pipe air purging should be carried out using the large compressors available in the production facility, or by utilizing the large storage tanks present in the facility to store air for intermittent purging ； The purging pressure must not exceed the design pressure of the pipeline, and the flow rate should be at least 20 m/s. When purging oil-free pipelines, the gas must not contain any oil ； During the air purging process, once it is visually confirmed that no smoke or dust is present in the exhaust gas, a wooden target covered with white cloth or painted white should be placed at the exhaust outlet for inspection; it is considered satisfactory if no rust, dust, moisture, or other debris is found on the target within 5 minutes. V. Steam Purging: When purging pipes with steam, the temporary pipes installed for this purpose should be fitted in accordance with the technical requirements of the steam pipes, and their installation quality must meet the specifications ； Steam pipes should be purged with high-flow steam, at a flow rate of not less than 30 m/s ； Before steam purging, the process should be carried out in a cycle of heating—cooling—reheating. During purging, it is advisable to purge one pipeline at a time, using a rotational approach ； For the steam pipes leading to the turbine or as specified in the design documents, the test target plates should be inspected after steam purging; when the design documents do not provide specific requirements, the quality shall be such that the marks on the target plates are no larger than φ0.6 mm in diameter and have a certain depth