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Buckling in pontoon and deck of flaoting roof tank

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Inspector89

Inspector89

Mechanical
Joined
May 26, 2018
Messages
30
Location
IN
Hi members,

In our facility, roof of the a crude oil storage tank (pontoon floating roof type) was filled 1m of crude oil as the roof drain pipe got corroded and the roof drain check valve did not function properly. The pontoons and the roof deck were found with buckling. On some pontoons and roof deck buckling was severe when compared with other areas. We do not want to replace the entire roof due to cost constraint and want to replace only the ones that definitely needs replacement. What is the allowable buckling on the pontoons and roofs.

 
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I'm not sure thet ate any hard and fast "rules" on this. It's all about serviceability.

So basically your roof sank?

Was it on legs at the time?

Loiks relatively easy to me but an experienced tank builder will give you much better info once they can inspect both sides.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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I think the design stress in those elements is going to be limited by buckling, so anything that reduces the buckling strength is going to be a weakening of the overall roof. Exactly what that limit is, I don't know.
One approach- assume a dented plate, per the sketch.
Find the maximum compressive stress allowable in the undamaged plate (probably pretty low for a wide plate).
Calculate bending at that dent. And from that, deduce how small that dent has to be before the bending is no longer significant.
SKETCH_xhmoac.jpg
 
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While landing, most of the legs got damaged. All the legs are going to be replaced.
For me the the plates of pontoons and roofs that were severely buckled (shart dent/peak like appearance) shall be replaced as they have stress concentration which may cause cracking during service. Where the buckling is not sharp and overly distrubited over a large area is somewhat acceptable for me.

Severe buckling noted on bottom deck of pontoon which is not acceptable

Bucking on bottom deck of pontoon which can be accepted


 
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Dear Inspector89,

Carry out chalk diesel test of the pontoon boxes to check for leaks. There would be, so carry out weld repair.

Fill up the opposite pontoon boxes with water to ensure no leaks.

Regards.

DHURJATI SEN

 
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