Tank Collapse

[Forging09]

I have just witnessed collapse of API 650 HFO tank because of very harsh wind effect in erection situation. it was collapsed at the last course of shell. The top of tank was open. Wind velocity is 160 km/h at site and tank is located near seaside. However tank was safe according to the min. requirement of intermediate wind gird namely H1>H and there was no need to put a wind girder.

Tank was subject to vacuum effect because of wind and collapsed. So what is your comment to this issue. What should have been done to prevent from this event?

 

[Unotec]

Not erect while the winds were that strong?
Was the tank fully assembled and in place?
What size tank?
Was it on a crane? Sloped? On a support?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[Unotec]

Oh, do post photos please

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[Bonswa]

In addition to Unotec's questions:
What type of roof? internal/external floating, Fixed?
How was it subjected to vacuum?

I have just witnessed the exact same thing after Hurricane Gustav. We have a 150' diameter x 40' high fixed roof tank. Not sure EXACTLY what the winds were, but estimate around 75-90 mph. We were in the process of replacing the entire roof and rafters due to corrosion. being a fixed roof tank, it didn't require an intermediate wind girder. We came back from evacuation, and the tank had collapsed on one side. it put a nice KINK in the shell.

 

[JoeTank]

Sounds like both cases may have involved the collapse of a tank that did not effective stiffness at the top of the shell. Am I right? So little info is offered it's difficult to render any opinion or comment.

Joe Tank

 

[JStephen]

The intent of the design rules of API-650 is that the completed structure will be adequate for the design conditions. Stability during erection is not covered by the standard, and is the responsibility of the erector. There have been different approaches used, including guy lines, stiffened scaffolds, etc. This is not just an issue with tanks, although they are particularly susceptible to wind damage during erection, but other structures can have similar issues.

 

[Bonswa]

Joe... that is exactly right. In my case, i forgot to mention, the roof and about 75% of the rafters were out. Before the roof removal, there was plenty stiffness. This didnt happen at my site, but at the site of another one of my customers.

JStephen... That's the first question i asked. "what happened to the guy lines?" apparently, the repair company didnt use any. Instead, they built a scaffold around the top course. That didnt do much.

Check out the pictures below. in the pictures, they've already removed the scaffolding in the damaged area, but you can see it around the rest of the tank.

http://i6.photobucket.com/albums/y220/bonswa/photo1.jpg

http://i6.photobucket.com/albums/y220/bonswa/photo2.jpg

http://i6.photobucket.com/albums/y220/bonswa/photo3.jpg

http://i6.photobucket.com/albums/y220/bonswa/photo4.jpg

 

[786392]

Dear All
In all Fairness if a tank is under maintenance/repairs in roofless condition then,either additional temporary safeguarding through especially welded eyes all along upper circumferential shell span be provided alongwith steel slings fastening to secure, or
There should have been special windgirder re-inforcements in-place on upper portion to counter possible foreseeable extreme stresses impact from very high wind loads described above.
Hope this Helps

Best Regards
Qalander(Chem)

 

[Forging09]

Dear Mr. Stephen,

Thanks a lot for your comment. Guy wire precaution had been taken while erection from several joints but stiffening scaffhold. Nonetheless, this collapse occured.

 

[Bonswa]

What about the other questions by myself and unotec?

 

[Forging09]

The tank is supported cone roof. Collapse is totaly same as indicated above photos by Bonswa . Tank is 20.000 cubic meter. But there was no hole and stiffening ring. There was only guy wire. As i said when tank collapsed wind velocity was measured 95 mil/hour.

I wonder if we had executed all precautions together guy wire ,hole and stiffening ring , would have tank been safe against vacuum effect by squeezing as a paper?? this is exactly a case study. Maybe sometimes engineering is not adequate. what do you think?

 

[Forging09]

Here is photo

 

[Forging09]

sory...i could not attach at previous message

 

[786392]

Dear Forging09 Hello/Good Morning, Definitely you shared a great learning info;especially the photos gave better insight.

However provision of some additional stiffening ring/ Windgirder as per special circumstance could have helped; since a roof less tank is quite similar in nature and response to a 'Floating roof Tank' and as such very difficult to sustain the described high wind load conditions otherwise.

Definitely it should be the mechanical disipline guys to come forward with better suggestion/ remedies.

Best Regards
Qalander(Chem)

 

[Bonswa]

I believe that in the case i described, they could have taken extra precautions, however they were ignorant to what the outcome would have been. In the case i described, it was a hurricane. They had plenty of warning. I can guarantee you that the next time they are in this situation and a hurricane is threatening, they will shift their priorities from construction to reinforcement. next time, i see them adding a temporary intermediate wind girder.

 

[chicopee]

Question: is the damage covered by insurance?

 

[JoeTank]

Just out of curiosity...
How wide are the shell courses? The second shell course from the top looks very narrow. API-650 rerquires a minimum of 6 ft (1.8m) wide. Also, how is the roof structure being stabilized?

Joe Tank

 

[786392]

True, there seem to be less wider sheets utilized in more than two courses.

The Photograph's close-up show that post damage conditions of all courses sheets are not of the same color and appearance;

as if there was some variation in the steel sheet's material quality used in fabrication.(can not say how much&how far?)

Best Regards
Qalander(Chem)

 

[Forging09]

Dear Joe Tank,

"API-650 rerquires a minimum of 6 ft (1.8m) wide." this is not strict as i know. All shell courses are in same material quality undoubtedly.

 

[Forging09]

And the subject is different you mentioned. This is vacuum effect Not related with material quality or roof structure. This should be known by erectors more deeply and should think twice when they install tank against hurricane.