Steel Tank Strengthening with CFRP

[AntoniosT]

Hi guys,

I am assessing large storage tanks to API 650 App. E, and some of them are failing the hoop stresses check. I must report back to the client the results including recommendations for potential retrofit solution to the problem.

I found on the internet that Carbon Fiber Reinforced Polymer (CFRP) is used for strengthening tanks. Due to the nature of the problem, it seems to me that this is the only solution.

Can anyone provide me with additional info about strengthening tanks by installing CFRP around the shell (material cost, installation cost, companies that offer these type of services, available brochures on the net etc).

Thanks

 

[JedClampett]

Why is carbon fibers the only solution? Can't you weld straps made of steel to the tank?

 

[AntoniosT]

I can see why “only” can be misleading.

Yes you could, increasing the thickness of shell at that location will be the easiest solution but these are oil tanks and hence must be emptied before any welding takes place. We are talking about 250,000 BBL tanks which are part of a bulk plant. As you can imagine business interruption is essential to the client, so I am looking for a solution which can fix the problem with limited business disruption to them. The only one I manage to find is CFRP.

 

[IFRs]

Have you looked in API 653 for guidance? Are you saying that the only overstress is due to seismic loading? The tanks may not have to meet current API 650 code - they may only have to meed the code in force at the time of construction - Section 3.4: "The standard used for repairs or alterations made after original construction is the as-built standard" and 4.3.3.5 "All other loads shall also be evaluated according to the original standard of construction"

 

[AntoniosT]

@IFRs

The scope of this assessment is to check the facility against the current standards. The purpose is to upgrade the facility. Even if you are right it makes no difference, I still have to report possible retrofit solutions to the problem.

 

[ChipB]

I've seen it used on concrete with great success. Call Sika directly and I'm sure they'll put you in touch with someone with that expertise.

 

[JedClampett]

If the CFRP has the same, or only slightly less stiffness, it will add strength in proportion to its area. If it has a considerably smaller E, the area will have to be proportioned using a ratio of the E's.
Also, if you want the CFRP to fully engage, the tank will need to be empty when it's installed. If you put it on when the tank is full, the static hoop stresses will be locked into the steel shell. You might still get an overstress.
This might not be as critical an interruption as emptying the tanks and ventilating them for welding.

 

[JStephen]

If you start winding a steel shell with fibers under tension in the way that a concrete tank is prestressed, buckling the shell would be a concern.

The simplest solution to the problem as described would be to derate the tanks for a lower maximum height until they can be modified or replaced.

 

[corrosionman]

AntoniosT,Before you could apply the CFRP it would be necessary to shotblast clean the required surface to achieve a bond . Will this be permissible inside the refinery area. We once strengthened (and fixed some very bad leaks) on a 70 foot dia tank by wrapping a 12 inch wide steel band around it. The " Band" was a number of curved flat strips with bolted connections at both ends.Experimentally we determined the torque in the bolts to give the required tension in the band so as not to overkill the tank wall.It was important that all the numerous bolted joints were tightened simultaneously.
Before applying the band we put a few layers of ordinary GRP on the wall. The job was considered a success.
However, I realise your tanks are huge compared wth ours.
Maybe you might tightly wrap a steel wire round the tank then overcoat it with grp which will bond the wire to the shell wall.
Cheers, Corrosionman

 

[ChipB]

I don't think Antonio is trying to send the steel into compression with his potential solution. As I said, I've seen it used on concrete. I guess I should have clarified and said I've seen it used to repair concrete. Also for seismic retrofit.

Personally, I'd be interested in finding out what they (Sika) would have to say about it. We come across vessels all the time which need to be reinforced. Whether they do it or not....

I came across the Sika Carbodur in the late 90s for repairing a university's chemistry lab floor in Florida.
Their website indicates steel reinforcing too.

I think the Carbodur Plates are what you'd be interested in.

http://www.sikaconstruction.com/con/con-repair/con-repair-ss.htm

 

[AntoniosT]

Thanks for your help

For now only outlining a potential solution is required and I am happy to report wrapping the tank with CFRP as one of them.
If they actually decide to do something about it, it would be interesting to see with what solution we will end up

 

[JStephen]

The reason that I mention putting the material on under tension is that if the elastic modulus is significantly less than steel, that's the only way you'd be able to get much of the normal hoop force transferred into it.