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?

 

[JoeTank]

Forging09,
I'm not exactly sure what you meant about "not as strict as I know". But, I did re-read API-650 about course width and it does permit narrower widths by agreement with the purchaser. The contractor may not make the decision to use narrower widths solely on his own.

Joe Tank

 

[JoeTank]

786392,
I do not think one can judge steel plate quality by a photograph and certainly not by the variation in mill scale presence on the plate surface. I have never heard of appearance as a factor in plate quality. Only material testing could reveal such conditions.

Joe Tank

 

[Forging09]

Dear Sirs,

Could you please show a way how i can calculate stiffening scaffold or a provisional stiffening ring section area while tank is open-top during erection to prevent from bending of plate against harsh wind or vacuum effect.

For instance, for 5000 m3 tank(Diameter=25m , Height=12m) is 140UNP ring adequate if it is put throughout circumferance in the middle of tank inside?
Wind velocity =160 km/h appr.

Thanks in advance for help.

 

[JoeTank]

Go to API-650, Section 5.9.6.1 for the calculation. Table 5-24 includes typical stiffeners sizes for open top tanks. Since it is past the hurricane season, why mess with this now? Just finsih the tank.

Joe Tank

 

[786392]

Dear Forging09,
I believe Joe's advice is Master advice indeed.
Any open top tanks as per API 650;as is the case for floating roof tanks with open tops.
Wind girders and adequate stiffening rings are mandated to retain/ maintain the shape.

Best Regards
Qalander(Chem)