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After passing the strength test and prior to the air pressure tightness test, steel pipes shall be flushed and purged in accordance with the requirements of GB50235-97 “Code for Construction and Acceptance of Industrial Metal Piping Works”. For many years, techniques such as water flushing, air purging, and steam purging have been primarily used for flushing and purging. This is quite effective for small-diameter pipes; however, for pipes with larger diameters, the ideal purging effect cannot be achieved because the flow rate of the purging medium does not meet the specified requirements. As pipeline accessories and instruments become increasingly sophisticated, the technical requirements for production processes continue to rise. Some construction techniques can no longer meet these requirements. In the construction of purging and flushing of large-diameter steel pipes, the blast purging method is gradually replacing other previously used construction methods. Blowdown cleaning involves sealing one end of the pipeline to be cleaned with a rupture disc whose strength is much lower than that of the pipeline, while compressed air is introduced at the other end. The air pressure within the system gradually increases; when it exceeds the maximum pressure limit that the rupture disc can withstand, the disc suddenly ruptures. The compressed air in the system then expands rapidly and is ejected from the rupture point at extremely high speed. Meanwhile, weld slag and other debris inside the pipeline are also expelled under the effect of the vibrations caused by the blasting and the impact of the high-speed airflow. Repeating this process several times ensures that the purging requirements are met. Preparatory work and construction requirements for blast purging: (1) The pressure test of the pipeline has been successfully completed, and the quality of the work meets the requirements stipulated in the construction specifications and design documents ； (2) The purging plan has been approved by the construction unit and the supervision unit, and is understood by all personnel involved in the purging ； (3) Orifice plates, flow meters, valves, etc. that must not be involved in the purging have been isolated; this purge pipeline has also been isolated from other adjacent pipelines and equipment ； (4) The selection of the blasting system is very important; it directly affects the degree of cleanliness achieved during system purging and the efficiency of the purging process. Generally, the division should be carried out based on the pipeline construction drawings and in conjunction with the actual process flow. Due consideration must be given to the effects of forces caused by blasting. Efforts should be made to minimize the number of temporary reinforcement points, while ensuring ease of connecting intake pipes within the system, installing pressure gauges, and replacing rupture discs. Additionally, there must be sufficient gas volume upstream of the system to guarantee the effectiveness of purging at that location ； (5) After the system is determined, the blast opening should be selected based on the actual installation site of the pipeline. The principle is that there must be sufficient space for blasting. Generally, there should be at least 10 meters of open space around the blast opening. It is preferable to locate it at the lowest point of the pipeline; if possible, choose a location at the end of the pipeline that is easy to protect. Typically, the blast opening is oriented horizontally or downward. Sturdy supports must be provided at the blast opening ； (6) Ordinary asbestos sheets can be used for blast discs, with a thickness of generally 1–3 mm. A “cross” or “plus sign” pattern can be marked on the asbestos sheet. A blast pressure of around 0.3–0.4 MPa is sufficient; too low a pressure results in more blasting attempts and makes it difficult for the blast disc to break, while too high a pressure is unsafe and can lead to injuries. Process characteristics and procedure of purging: The blasting purging technique is employed for purging large-diameter steel pipelines. This method has the following characteristics: (1) The flow velocity of the purging medium is high (not less than 15 m/s), providing strong carrying capacity; it can remove soil, welding slag, residual water accumulated in low-lying areas of the pipeline, and other debris ； (2) High purging efficiency. For pipelines of the same specification and length, blasting and purging 4 to 6 times is generally sufficient to meet the cleanliness requirements ； (3) Due to the high speed of the blasting purge airflow, not only rust and debris are blown out. Debris located in dead corners of the pipeline is also carried away by the rapidly expanding airflow due to the vibrations caused by detonation, significantly improving the cleaning efficiency ； (4) For large-diameter pipes, it is difficult to find suitably sized air sources; thus, the quality cannot be easily guaranteed. Blast purging is particularly suitable for large-diameter pipes ； (5) Compared to other flushing and purging methods, blast purging requires less equipment and materials (the main equipment is an air compressor, with atmospheric air serving as the gas source). It saves labor, time, and costs; it also has low technical requirements, making it easy to promote and apply ； (6) It can be used for medium- and large-diameter steel industrial pipes with diameters ranging from DN100 to 600 mm. When applying this purging technique to steel pipelines with a diameter less than DN200mm, electric butterfly valves can be used in place of rupture discs; by rapidly opening and closing the valves, the same effect as rupture disc purging can be achieved. Purging process flow: Determine the purging system → Install temporary blind flanges (to isolate equipment and systems that cannot be purged) → Install pressure gauges (temporarily reinforce local pipelines and pipe supports) → Open all valves in the system → Install rupture discs → Charge with gas → Trigger rupture → Quality inspection and target testing (if unsuccessful, repeat the process starting from the step of installing the rupture disc) → Acceptance