Regarding blast purging, a few simple questions

This post was last edited by qy576100527 on 2017-7-15 at 13:05. Blasting purging is not effective when the pressure of the purging gas is low and the pipelines are too large to be purged properly. 1. It has high efficiency, as it uses the force of detonation to remove debris from within the pipes. 2. Blasting discs are usually made of asbestos sheet or aluminum foil. 3. Wires are used near the blasting site to hold back debris, preventing it from causing injury to people

Blowout cleaning is highly efficient; the larger the pipe diameter and the longer the pipeline, the more effective this method is. In the absence of a container acting as a gas tank, a larger pipe can hold more gas, and the strong airflow generated during blowout helps to remove impurities from within the pipeline. For pipelines with relatively small diameters, it is best to use a pressure-resistant container connected to the same process as a gas tank for blasting and purging, as this yields better purification results. There are usually special blast discs available for sale.

GB50235-97 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\"

Answer from Baidu search: Blasting purging involves sealing one end of the pipeline to be purged with a blast 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; once it exceeds the maximum pressure that the rupture disc can withstand, the disc ruptures suddenly, and the compressed air in the system expands rapidly and is ejected at extremely high speeds through the rupture opening. At the same time, the slag and other debris inside the pipeline are also expelled as a result of the vibrations caused by the blasting and the impact of high-speed air currents. Repeating this process several times will meet the purging requirements. Preparatory work and construction requirements for blasting purging: (1) The pressure test of the pipeline has been successful, and the quality of the work meets the requirements specified in the construction standards and design documents ； (2) The purging plan has been approved by the project owner and the supervision unit, and is available for those involved in the purging process to refer to ； (3) Orifice plates that are not allowed to be involved in the purging process. Flowmeters, valves, etc. have been isolated, and this purging pipeline has also been separated from other adjacent pipelines and equipment ； (4) The selection of the blasting system is very important, as it directly affects the cleanliness of the system cleaning process as well as the efficiency of that process. Generally, the division should be based on the pipeline construction drawings along with the actual process flow. Full consideration should be given to the effects of forces caused by blasting. Temporary reinforcement points should be minimized as much as possible to facilitate the connection of intake pipes within the system, the installation of pressure gauges, and the replacement of blast valves. Moreover, there should be sufficient air capacity upstream of the system to ensure the quality of purging in that area ； (5) Once the system is determined, the blasting point should be selected based on the actual installation location of the pipeline. The principle is that there must be sufficient space for blasting. There should generally be at least 10 meters of open space at the blasting point; it is advisable to locate it at the lowest part of the pipeline, preferably at one of its ends in a location that is easy to protect. The blasting direction is usually horizontal or downward, and a sturdy support should be in place at the blasting point ； (6) Ordinary asbestos sheets can be used for rupture disks, with a thickness of generally 1–3 mm. A “+” or “X” pattern can be marked on the asbestos sheet; the rupture pressure is usually between 0.3 and 0.4 MPa. If the pressure is too low, the number of ruptures increases and it becomes difficult for the rupture disk to break, while if the pressure is too high, it is unsafe and can lead to injuries.

Wouldn’t it be better to carry out manual cleaning with such a large diameter? The blasting purge should proceed from the end toward the outlet, with the purging effect becoming gradual. It is necessary to clean the pipes before butt welding; for pipes of such large diameter, the main area that needs cleaning is the internal weld seam. Manual cleaning yields better results, and the cleaning (treatment) before pipe joining is also superior to blasting cleaning.

What I want to know is, does it require removing the flange and installing a new one every time a burst disc is blown? Since I am in North America, I use quick-opening butterfly valves. Pressure is indeed relatively easy to control, but the problem is that the largest diameter available for quick-opening butterfly valves is DN350; for pipelines with larger diameters, there are concerns that the performance will not be good. I am discussing the plan with the project team. I personally prefer to use workwear, as the advantage is efficiency, since it eliminates the time required for installing and removing blast discs.

It has to be installed again each time; it’s usually a ring-shaped gasket, just a ring with several screw holes on it – you can cut one temporarily – and those holes should match those of the blowout port’s bolts. An asbestos gasket is placed in between; the number or thickness of such gaskets depends on the blasting pressure required. When installing the blasting gasket, tighten the bolts diagonally: 4 bolts, 6 bolts, or 8 bolts if the pressure is higher, as long as there are no leaks. It’s not necessary to tighten all the bolts. As the saying goes, preparing the tools doesn’t delay the work, and it’s actually quite fast. For steam pipelines, it’s better to use quick-release valves, after all, it’s dangerous

There is no need for molded flanges; temporary pressing plates can be made from steel plates on site, and they can be secured using asbestos sheets. It’s also not necessary to use bolts on all locations – using just half of the bolts is sufficient, which makes blasting and cleaning much easier. The blast panel can be made of asbestos board or aluminum foil for insulation

As for asbestos boards, that’s how it is in our company