Regarding pipeline cleaning and purging

The purging method should be determined based on the usage requirements of the pipeline, the working medium, and the degree of dirt on the inner surface of the pipeline. For liquid or gas pipelines with a nominal diameter of 600 MM or greater, manual cleaning is recommended; for liquid pipelines with a nominal diameter of less than 600 MM, water flushing is advisable ； Gas pipelines with a nominal diameter of less than 600 MM should be purged with air ； Steam pipes should be purged with steam ； Non-thermal pipelines must not be purged with steam.

This standard does not impose strict requirements, and flexibility is needed in its application. In some cases, liquid pipelines cannot be flushed with water, such as with heat transfer oils or special chemical liquids, as moisture must not mix into these substances.

The regulatory requirements really cannot be changed arbitrarily.

It cannot be generalized; compressed air and water have their own advantages and disadvantages when used for purging: compressed air is readily available, can be used for blasting purging, and is easy to discharge； Water requires high-capacity pumps and a designated discharge area, conditions that general contractors may not be able to meet. Therefore, our approach is to use air purging for large-diameter pipes below DN600, while water purging is suitable for small-diameter pipes below DN600. Of course, this applies to pipes that have no special requirements regarding the medium. For example: in addition to steam lines, oil lines, and pipes that require drying. The effectiveness of purging is also related to factors such as the layout of the pipes to be purged, the purging sequence, and the diameter of the exhaust ports.

The method of purging is determined based on the medium being transported through the pipeline; when both liquids and gases can be used for purging, it’s worth considering the costs.

This post was last edited by clguan on 2009-9-6 at 20:52. Personal opinion: 1. Liquid pipelines (DN<600mm) are flushed with water instead of being purged with air because it is more convenient to use water on site, or rather, it is easier to obtain water compared to compressed air. 2. In cases where pipelines for transporting liquids have strict requirements regarding water content due to the properties of the medium, air is also used for purging. Therefore, the choice of medium for flushing or purging the pipelines is not fixed; it is determined based on the actual circumstances. 3. Moreover, according to GB50235 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\", it is specified that the medium to be used should be one that is \"preferable\" rather than one that is \"required\"” ； Therefore, a literal interpretation suggests it should depend on the circumstances, rather than having to be followed strictly in this manner. 4. GB50235 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\" and SH3501 \"Code for Construction and Acceptance of Piping Projects for Toxic and Flammable Media in Petrochemical Industries\" contain detailed regulations regarding the flushing and purging of pipelines. For reference!

Compressed air purging has two drawbacks: first, the pressure is generally not high, and second, the capacity of the compressor is limited. These two factors restrict the range in which compressed air can be used for purging; it is typically applied to small pipes as well as pipes with low pressure, and is also often used for airtightness tests involving pressures below 6 kilograms.

It can’t be said that air is better than water; regarding purging, one must follow the relevant specifications, as there are certain pipelines for which water cannot be used. It is still more reliable to refer to the specifications.

Using only air blowing can remove only the loose dust on the surface, but it is ineffective against rust, oil, and similar substances. It depends on the system’s conditions and requirements to decide what to use