Tilted compression (stiffener) ring

[Abdo2007]

Dear All

We have tanks with a deformed top compression ring. This took place in a three out of four 35 years old single cladded shell, fixed roof tanks.(D = 32 m, H = 18 m).

The cause?

in my opinion it could be:
1) an uneven settlement
2) a wrong erection procedure (i.e., it is there from day one but no one noticed as the tanks are insulated)

No shell buckling or bulging

The vertical side of the stiffener beam is tilted radially inward for 12 to 25 mm for 40% of the circumference. see images plz.


Your support is highly appreciated.

 

[r13]

I would 1) check leveling of the tank bottom ring and the roof edge to substantiate your first concern, and pinpoint the source of movement; and 2) check the welds on the roof and the tank wall, which can be cracked due to the movement. Then find the causes.

 

[HTURKAK]

The information that you provided is not enough to see the case.. Pls provide more info . to get valuable comments such as ; The design and operating temperature and pressure, roof supporting system, connection detail of roof plate to ring , some settlement measurements, the deformation is local or not, insulation and cladding system, some descriptive pictures..

With the info. that you provided , the posts that you will receive will be only guessing game... I will start the first guess;


The internal pressure built up and the roof plate ovalized and developed radial tension all around ..the roof plate connection to sloped stiffener experienced bending ..

 

[MJCronin]

Has the tank ever been repeatedly overfilled ?

Has there ever been a seismic event in your area ?

Where is the tank located ?

Can you provide pictures ?

MJCronin
Sr. Process Engineer

 

[saplanti]

If the deformation is uniform all around it may be caused by the pressurising the tank. Sometimes, the pump introduce the fluid with high flow rate, and the air discharge vent size is not sufficient not to cause pressurisation this can happen. Similar effect can happen in forms of buckling on the tank when the discharge pump rate can cause vacuum with insufficient vacuum breaker size.

 

[Dhurjati Sen]

It seems that the welding has opened up at places. Quite common for such old tanks. When was the last external inspection done? How is the paint condition of the tank, specially around the compression ring?

DHURJATI SEN