Bulge in Vessel Skirt

[KernOily]

Hi guys. I have been asked to look at a vertical vessel (a gas compressor skid suction scrubber) that has a bulge in the skirt. The owner is concerned about fitness-for-service. I am trying to get more details, like how did the bulge get there, but in general how would one make the assessment? Do I need a forensic specialist that can run an FEA on the bulge and provide an opinion?

Thanks guys! Pete

 

[chicopee]

About showing pictures of the bulge, the affected areas around it and the remaining portion of the scrubber, that way we can make some educated guesses as to what caused the bulge.

 

[JStephen]

When a cylindrical shell is overloaded axially, it can buckle in a classical sense, or it can form a bulge around the perimeter, known as an "elephant's foot bulge", and this is what your description sounds like. This is most common with seismic loading in flat bottom tanks. I just recently saw a silo with such a bulge partway up, and that would have been from grain sliding against the shell, loading the shell in compression.

I would suggest to check the stresses in the shell in the operating condition. If the shell is currently underdesigned, or seems borderline, it should be repaired or modified. If the shell calculates out okay, it may have been damaged by seismic action or by handling when setting, etc, and in that case, MAY be okay until the event happens again- and probably should be repaired in that case as well.

If the bulge does NOT look like elephant's foot bulge, please disregard the above and get us a better description!

Some online photos:

http://www.structuremag.org/images/0307-cs-5.jpg

http://saprefresh.oes.ca.gov/images/reservoir.jpg

http://lef.uprm.edu/Failure of two Tanks/Examples earthquakes.html

 

[JohnGP]

To have a bulge in the skirt seems to suggest that the skirt was not correctly designed for all possible loading conditions. It may be possible to just stiffen (being not part of the pressure envelope), but of concern may be any additional stress on nozzles or connected pipework if bulge in the skirt has upset alignment of the scrubber. Pure conjecture though.

 

[TGS4]

Get an expert in Fitness-For-Service assessments. It may not necessarily need an FEA, but an FFS expert will know all of the right questions to ask to try to ascertain what happened, how it happened, and how to repair/mitigate it from happening again.

 

[metengr]

The assessment better include surface NDT to evaluate the extent of damage and repair.

 

[KernOily]

Thanks for the help guys. I am waiting for photos and additional info to show up. Thank you! Pete

 

[SNORGY]

This will have ripple effects throughout all connected piping for a couple of supports away from the vessel, too.