Design for which liquid level? HLL or NLL? 2

[ConstantEffort]

What is the common industry practice concerning vessel design liquid level?

Code review, google search, and eng-tips search didn't give me any clues.

Is it "double jeopardy" to consider a seismic event while the vessel is filled to the HLL? From a simplistic view, any liquid level between LLL and HLL is acceptable for operations.

 

[marty007]

We always design for the highest liquid level provided to us by the client (HLL, HHLL, or some other designation altogether). The truth is that as the vessel fabricator, I have no idea how their control system will be operating things, and I have to be confident that the equipment is safe.

 

[SnTMan]

Echoing marty007, design for flooded if possible, hydrotest. Might be able to ease this for a tall vertical vessel that WILL NEVER be flooded.

Regards,

Mike

 

[doct9960]

SnTMan,
Never say never. It happened on a distillation tower in the BP Texas City refinery back in 2005. Fifteen workers were killed and around 180 were injured.

http://www.youtube.com/watch?v=XuJtdQOU_Z4

ConstantEffort,
I work for an engineering company. We consider seismic loading on vessels at the highest operating liquid level (e.g. HLL, HHLL). We don't consider seismic loading during upset condition (i.e. full of liquid or flooded during operation). The probability of an earthquake occurring during upset conditions is so remote.

Process engineers are responsible for telling us if the vessel needs to be designed for upset condition . If Process does not give any info about this condition, it is prudent to ask for it, especially for very tall towers. Bottom shell courses may need to be increased in thickness or the flange rating of bottom nozzles may need to be bumped up.