【Weekly Topic】Further discussion on whether vacuum pipes belong to pressure pipes (August 1 – August 6)
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This post was last edited by security on 2011-8-1 08:56. There have been similar discussions on this forum regarding whether vacuum pipes are considered pressure pipes; to draw more attention to this issue, a new thread is started for discussion. All experts and colleagues are welcome to join in! According to Article 99 of Chapter 8 of the Regulations on the Safety Supervision of Special Equipment, issued in 2003, a \"pressure pipeline\" is defined as a tubular device that uses a certain pressure to transport gases or liquids. It refers to pipelines in which the maximum operating pressure is greater than or equal to 0.1 MPa (gauge pressure), and which are used for transporting gases, liquefied gases, steam, or liquid media that are flammable, explosive, toxic, corrosive, with a maximum operating temperature greater than or equal to their standard boiling point; such pipelines also have a nominal diameter of more than 25 mm. ” According to the provisions, pipelines with a design pressure of less than 0.1 MPa are not considered pressure pipelines, regardless of whether the medium is extremely or highly hazardous. In accordance with SH3501, Code for Construction and Acceptance of Pipelines for Highly Toxic and Flammable Media in Petrochemical Industries, 1.0.1 This code applies to the construction and acceptance of new, modified, or expanded steel pipelines for highly toxic (extremely hazardous and highly hazardous) and flammable media in petrochemical enterprises, where the design pressure ranges from 400 Pa absolute to 42 MPa gauge pressure (400 Pa absolute includes the vacuum range from 400 Pa to 0.1 MPa), and the design temperature ranges from -196 to 850 degrees. 1.0.6 Units responsible for the construction of pipelines carrying highly toxic or flammable media must hold the corresponding pressure pipeline installation license issued by the quality and technical supervision authorities. 1.0.7 Welders working on pipelines involving highly toxic and flammable media must take examinations in accordance with *** and obtain a qualified certificate. Non-destructive testing personnel should **** It can be seen that although vacuum pipes do not fall under the category of pressure pipes, they still require regulation; the installation companies must be qualified, the welders must be qualified, and the non-destructive testing personnel as well must be qualified, and so on. Can it be concluded then that vacuum pipelines are also exempt from the regulations applicable to pressure pipelines (such as various permits), but that they still meet all the other requirements in the same way as pressure pipelines?
In my personal opinion, it belongs to pressure pipelines. In systems with a high vacuum level, the pipes are subjected to a large negative pressure.
According to 1.3 of GB2080.1, \"Pressure pipelines for liquids with a nominal diameter of 25 mm or less, a maximum operating pressure of less than 0.1 MPa or in a vacuum state, and that are non-flammable, non-toxic, and non-corrosive may also follow these specifications; however, they are not subject to safety supervision and are not included in the pipeline classification system.\" ” It has been clarified that it falls outside the scope of regulation.
In my opinion, vacuum pipes fall under the category of pressure pipes; although the pressure inside such pipes is negative during normal operation, it can be positive when the system is shut down or in the event of an accident. It depends on whether the test pressure for these pipes is greater than 0.1 MPa.
Not to mention pipelines, even vacuum vessels do not fall under the category of pressure vessels; therefore, vacuum pipelines should be considered pressure pipelines.
Reply to 1# RichardChan: The pressure acting on the pipes of the vacuum system is the external atmospheric pressure; therefore, the design pressure should be set at 0.1 MPa corresponding to this external pressure. Pressure pipelines with a design pressure of over 1 kilogram should not be classified as pressure pipelines
If one of the conditions for pressure pipelines is met, it is considered a pressure pipeline
Personal opinion: 1. Vacuum pipes do not fall within the scope of supervision for pressure pipes — Reason: The definition of pressure pipes and the scope of safety supervision are clearly specified in the Regulations! Moreover, it is only when all three conditions are met that a pressure pipeline falls within the scope of supervision! 2. SH3501 is an industry standard and also a construction acceptance specification ； Generally, industry standards are stricter than **standards. It is also reasonable to impose stricter requirements on the manufacturing, construction, and inspection of pipelines that transport highly toxic and flammable petrochemical substances. But this does not mean that vacuum pipes transporting highly toxic and flammable media can be concluded to be pressure pipes under supervision! Let’s discuss together!
I believe vacuum pipes fall under the category of pressure pipes, as pressure can be either positive or negative. The direction of the forces acting on ordinary pressure pipes is different from that in vacuum pipes, but their destructive power is the same...
Neither vacuum vessels nor vacuum pipes are considered pressure vessels; they fall outside the scope of safety supervision, nor are they included in pipeline classification systems. SH3501, the Code for Construction and Acceptance of Pipelines for Highly Toxic and Flammable Petrochemical Media, is merely a stringent technical specification based on industry standards applied in specific environments; it cannot replace national standards. Therefore, vacuum tubes are not considered pressure pipelines and are not subject to safety supervision.
Even in a vacuum environment, the pipeline must withstand the external pressure exerted by the atmosphere; the pressure simply shifts from the inside to the outside, but there is still a pressure difference. In my opinion, it would be more appropriate for the standards to specify what range this pressure difference should fall within