Questions about gaskets
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This post was last edited by sssshack on 2016-3-7 09:19. GB20801, Chapter 5.1.9.5 states that gaskets made of flammable materials such as rubber shall not be used in pipelines transporting strongly oxidizing media. So, is polytetrafluoroethylene considered a flammable material? If so, what kind of gaskets can be used on sulfuric acid pipelines? Graphite gaskets are dirty and fragile, so they aren’t very suitable. I would like to ask again: for sulfur dioxide gas, liquid chlorine, and liquid ammonia, what kind of gaskets are generally suitable? Also, should flammable and explosive media not use PTFE gaskets to prevent them from melting and leaking in the event of a fire?
http://www.baike.com/wiki/%E8%81%9A%E5%9B%9B%E6%B0%9F%E4%B9%99%E7%83%AF Please refer to the material properties section.
Polytetrafluoroethylene: The melting temperature is 327–342°C. The polytetrafluoroethylene gasket installed on-site does not meet any of the conditions required for combustion.
You can download the materials at http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1550213&highlight=hg. The materials are excellent, providing comprehensive guidelines for selecting gaskets and flanges
Paragraph 5.1.9.5 of GB20801 Book 3 states that gaskets made of flammable materials (such as rubber) shall not be used in pipelines transporting highly oxidizing media. So, is polytetrafluoroethylene considered a flammable material? If so, what kind of gaskets can be used on sulfuric acid pipelines? Graphite gaskets are dirty and fragile, so they aren’t very suitable. For concentrated sulfuric acid, it is recommended to use PTFE gaskets (modified PTFE gaskets are particularly suitable). Additionally, I would like to ask what kind of gaskets are generally appropriate for sulfur dioxide gas, liquid chlorine, and liquid ammonia. (For sulfur dioxide and liquid ammonia, modified polytetrafluoroethylene or flexible graphite can be used; for liquid chlorine, caution is required, and it is recommended to use modified tetrafluoroethylene filled with barium sulfate.) Also, cannot polytetrafluoroethylene gaskets be used for flammable and explosive media, in order to prevent melting and leakage in the event of a fire? (It is recommended to use gaskets with fire-resistant certification, such as Fluorocarbon High-temperature Loctite)
For sulfuric acid, polytetrafluoroethylene gaskets can be used; for liquid ammonia, 316L SS-PTFE wound gaskets are suitable
PTFE is flame-retardant by nature, so it does not burn; sulfuric acid can be used with PTFE material
Using acid-resistant asbestos gaskets for sulfuric acid is also feasible
For concentrated sulfuric acid, RPTFE that has been modified is used. As for sulfur dioxide and liquid chlorine, dry sulfur dioxide and pure liquid chlorine are involved, so metal-wound gaskets are used in these cases – specifically stainless steel wound with graphite. However, for liquid ammonia, I don’t think PTFE or graphite would be suitable, as liquid ammonia is generally treated as a liquefied hydrocarbon, and therefore metal-wound gaskets should be used.
Thank you for your reply. The selection of the appropriate gasket depends on factors such as the actual properties of the medium, temperature, pressure, and operating conditions. I was wondering what material combination will be used for the gasket used with liquid ammonia in this case; could you please let me know? This will help me conduct further verification, discuss the matter with you, and work together to improve the solution. Thank you
I chose the stainless steel wrapped with graphite one