shell reparation 5

[mectarek]

we have a crude oil storage tank that has a very damaged 1st shell. Pittings are Spread on most of the underside area of the 1st shell plates( about 40 cm from the bottom). the thickness loss is in some places about 66% of the original thickness.

the shell original thikness is 22 mm ( 0.866 in)
the storage tank Diamiter is 60.8 m (200 foot)

what do you think is the best reparation strategy?

 

[bimr]

It is common practice to replace the first shell ring. The tank is supported using temporary supports and clips during this procedure.

 

[chicopee]

Shell reparation--Hum???? Bimr, I don't think that's what Mectarek meant in your reply.

 

[mectarek]

chicopee, exactly I'm not talking about the bottom ring. i'm asking about the shell reparation

 

[IFRs]

Repairing the shell plate may cost more than replacing it. However, your original post says "underside area of the 1st shell plate" and I don't understand how a shell plate has an underside. It has an inside and an outside. It is common to refer to the vertical shell plates as "rings" or "courses". It is not uncommon to have corrosion on the inside of the shell plate in crude oil service particularly if there is a layer of water on the bottom. Replacing the shell plates in the areas of the corrosion is your best choice.

 

[mectarek]

thanks IFRS, and pardon my bad english

 

[bimr]

It is common to also replace the tank bottom at the same time that the first shell ring is replaced.

 

[MJCronin]

Just out of curiosity, regarding the corrosion and the repair of this crude storage tank...

- How old is the tank, what type is it and what types of crude was stored ?

- Was there a protective inner coating on the tank and is this repair due to a coating failure ?

- Did the tank corrode at the chine or was the failure through the tank bottom ?

- Do you plan to use protective coatings inside of the repaired tank If so, which type of coating will you use ?

Thank you and best regards ....

MJCronin
Sr. Process Engineer

 

[selva70]

Better to replace first shell course and coating is must inside the first shell course

 

[mectarek]

MJCronin, the Tank is not very old. It was built in 2002. the crude oil is Sahara Blend with a API gravity of 45°
yes there was a protective inner coating and this repair is due to coating failure.
the hole tank bottom is corroded and we are consedering a seconde bottom option
we are planning to use protective coatings. the bi-component type.

 

[teokal]

Hi, I made a similar thread (

http://www.eng-tips.com/viewthread.cfm?qid=406280),

refering to partial replacement of 1st shell course... But with partial I mean (client means in fact) replacing the 1st shell course in full circumference, but for half of the course's height...
What do you think?

Only best result in absolutely necessary time