Vessel Nozzle Location
Fabricated cyclindrical vessels, usually with hemispherical, torispherical or rounded ends, are used widely for storing liquids. Inevitably this leads to engineers wanting to locate nozzles on the vessel e.g. electrical engineers may want to insert a tank heater, instrument engineers may want to install
level instrumentation, and of course piping engineers will want to provide piping for filling and emptying.
There are mechanical and fabrication constraints on the location where nozzles can be placed i.e. how close to the edge of the vessel a nozzle can be located, consequently fabricated equipment engineers have come up with the following best practice (rules of thumb) for locating nozzles;
Nozzle Location on Horizontal Vessels
For non-radial nozzle to vessel intersections, as depicted above, the angle between the axis of the connection and a line normal to the shell surface should not exceed 50°.
Nozzle Location on Dished Ends of Vessels
The most common type of dished end on a vessel is an elliptical end. Nozzles in the elliptical ends of vessels should be avoided where possible. If it is not possible then no part of the nozzle should be closer than one tenth of the diameter of the vessel from the edge of the vessel.
Nozzle Location near Seam Connections
It is important to know where the seam between the cylindrical section and the dished end of a vessel is located. It is advisable to avoid any cutting or welding within approximately 50 to 75 mm (2 to 3") of the welded seams in order to avoid any added stresses due to heat buildup during the cutting and welding. Therefore nozzles should not be located close to these vessel seam connections.
Location of Nozzles for Instrumentation
The following rules of thumb provide a good starting point for locating vessel nozzles that will be used for instrumentation:
- Level Instrument nozzles should be as far from the fluid inlet nozzle as possible to avoid any turbulence present at the inlet end,
- Vapour pressure nozzles to be on the top of the vessel, near to the vapour outlet nozzle,
- Liquid temperature nozzles to be in the lower liquid region. And crucially, insure that sufficient space is usable for removal of the temperature element.
- Ensure all instrument nozzles are easily accessible. This may include from vessel ladders,
- Instrument nozzles, (in fact all nozzles) should not be located within the davit swing area of the access manway.
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