Pressure value used for cleaning pipes by blast purging method

Generally, when using the blasting and purging method to clean pipes, the pressure level to be applied should be selected based on the actual conditions. For some longer and more complex piping systems, higher pressure values are usually required for cleaning in order to ensure effective cleaning results and efficiency. However, when using high pressure values, it is also necessary to pay attention to the tolerance of the pipes, in order to prevent them from rupturing or being damaged due to excessive pressure. Therefore, before cleaning the pipeline, a comprehensive inspection and assessment are required to determine the best cleaning method and parameters suitable for that pipeline. .

Provisions for purging steam pipes: Steam pipes should be purged using steam. For non-steam pipes, if purging with compressed air does not meet the cleanliness requirements, steam can also be used for purging; however, it is necessary to consider whether their structure can withstand high temperatures and thermal expansion. The purging of steam pipes starts with the main air valve, and is carried out in stages. Along the direction of steam flow, 1 to 2 valves or flanges on the main and branch pipes are temporarily removed, so that each section of the main and branch pipes can be purged first, followed by the purging of the branch pipes and condensate pipes. During purging, usually only one exhaust port is used at a time, with the exhaust pipe leading to a safe location outside; the diameter of the exhaust pipe should not be smaller than that of the pipe being purged. During steam purging, a small amount of steam is first introduced slowly into the pipes to preheat the piping system; at the same time, attention is paid to monitoring the extent of thermal expansion of the pipes. The temperature is maintained at this level for 1 hour. Once the temperature difference between the beginning and end of the pipe section being purged is minimal, the amount of steam used is gradually increased. After that, the temperature is allowed to drop naturally to ambient levels, after which it is raised again and held constant for a second purge cycle. This process is repeated at least three times, with each cycle lasting 20–30 minutes. Purging can only be stopped when the steam discharged from the exhaust outlet is completely clean. Once the purging is complete, the main valve should be closed to remove any remaining gas and condensed water from the pipe, the exhaust pipe should be removed, and any issues identified during the heating and purging process should be addressed. During the purging process, steam traps should not be used to remove condensate from the system; it is better to temporarily remove them and reinstall them after the system has been purged and cleaned. Procedures for purging compressed air pipelines: Compressed air pipelines are generally purged using air, and the methods and steps for purification are the same as those for steam pipelines. During the purging process, the pipe wall must be continuously struck with a hammer to dislodge dirt such as rust that is adhered to the inner wall of the pipe, so that it can be blown away. Provisions for purging oxygen pipelines: After the oxygen pipelines pass the integrity test, they must be purged using oil-free air or ammonia, with an airflow velocity of not less than 20 m/s, for a continuous period of 8 hours. The methods and procedures for purging can follow the general guidelines for pipeline purging and cleaning; all pipelines should be purged thoroughly, without any remaining dead corners. Provisions for purging acetylene pipelines: After the acetylene pipelines pass the integrity test, they must be purged with compressed air to ensure they are clean. When the pipeline is put into use, it should also be purged with ammonia in an amount three times the volume of the pipeline, to drive out the air accumulated inside it. During purging, a valve and an exhaust pipe are installed at the end of the pipeline to release air; purging is considered successful when the oxygen content in the discharged ammonia is less than 3%. During purging, it is necessary to prevent air from accumulating in areas of the pipeline that cannot be reached by the purge flow ； After successful purging, acetylene is introduced into the pipe while it is filled with ammonia, and then it is put into use. Provisions for purging gas and natural gas pipelines: After the construction or maintenance of gas and natural gas pipelines is completed, compressed air at a pressure not lower than the operating pressure of the pipelines should be used for purging, in order to remove various debris that may have entered the pipelines during construction; this debris is then removed through vents, manholes, etc ； The purging methods and steps are the same as those for oxygen pipelines; however, before putting them into operation, gas pipelines must be purged with gas, and natural gas pipelines should be purged with natural gas, until the discharged gas passes the testing requirements. Regulations for purging oil pipelines: Oil pipelines that have been out of use for an extended period, as well as those that are in regular use, must be purged during maintenance to remove any oil remaining inside the pipes. Due to the high temperature of the steam, it can melt the residual oil accumulated on the pipe walls, cleaning the pipeline, which is why high-pressure steam is generally used for purging oil pipelines. After the purging is complete, any condensed water remaining in the pipes must be removed completely. Oil pipelines can also be purged with compressed air, the advantage of which is that no condensate water mixes into the oil.

WeChat official account: Petrochemical Engineering Notes； There is an article inside on the selection of purge pressure.

May I ask which standard the 0.6 MPa value comes from? Thank you.

I went to take a look; I didn’t see any standard criteria, only empirical parameters. Cannot be used as a reference.

A purging plan was prepared, but no standard basis could be found; it was basically based on empirical values. For some pipelines, the blasting pressure is determined by referring to the forces that the pipeline supports and hangers can withstand, so as to select a relatively safe blasting pressure. Papers on pipeline blasting and purging are also based on the empirical values derived from projects.