Wetted Surface of S&T exchanger
Wetted Surface of S&T exchanger
(OP)
Recently I joined a discussion about safety considerations for external fire scenario. When calculating the wetted surface for protecting the tube side of an heat exchanger it was discussed whether to include the shell surface and the heads or whether to include just the head surfaces. There were basically two opinions:
1. The fluid in the tubes is not in direct contact to the shell side, therefore the shell surface does not have to be considered.
2. For heat exchangers with liquid (!) on the shell side, the heat transfer coefficient through the tube walls during a fire scenario becomes considerable high, therefore the surface of shell AND heads has to be considered to stay on the safer side.
The latter approach seems to be quite conservative but actually I have seen both approaches in different projects several times and couldn't find anything in API521 about it. I would appreciate your comments to this topic! Thanks!
1. The fluid in the tubes is not in direct contact to the shell side, therefore the shell surface does not have to be considered.
2. For heat exchangers with liquid (!) on the shell side, the heat transfer coefficient through the tube walls during a fire scenario becomes considerable high, therefore the surface of shell AND heads has to be considered to stay on the safer side.
The latter approach seems to be quite conservative but actually I have seen both approaches in different projects several times and couldn't find anything in API521 about it. I would appreciate your comments to this topic! Thanks!





RE: Wetted Surface of S&T exchanger
RE: Wetted Surface of S&T exchanger
The API521 code mentions neither heat exchangers, pumps, piping strainers etc....etc..
It is my understanding that these components do not require a fire protection evaluation and the possible addition of relief devices. Whereas there is a real risk of an API-650 tank experiencing overpressure and rupture almost immediately during the first minutes of a fire, the same is not true for segments of piping in the same area.
Futhermore, the liquid volume contained is typically much, much smaller
The need for fire protection of all non-tank components should be addressed during a HAZOP
-MJC
RE: Wetted Surface of S&T exchanger
RE: Wetted Surface of S&T exchanger
-MJC
RE: Wetted Surface of S&T exchanger
In case of fire you should consider the shell side, the tube channel surface is much smaller than the shell, also if the HE is insulated you reduce the relief flow.
In case of fire there will be no temp difference (thermodynamics...) between the shell and tube sides so if you protect the shell side it is protecting also indirectly the tube side.
regards,
roker
RE: Wetted Surface of S&T exchanger