Reinforcement plate installed to keep tolerance inside of tank 3

[Eduardo1982]

Hey guys.
Is in the API 650 code any paragraph that forbid to use reinforcement plates intalled inside of the tank to keep and fit peaking & banding tolerances?
I attach a picture that shows plates welded. Personally, I think that it is a bad practise and it can affect the performance of the tank life introducing residual stress. In adittion I think that these plates can be corrosive points in a near future.

 

[HTURKAK]

I just see alignment lugs, plates attached by welding for erection purpose and they are Temporary attachments .

API 650 states,

 

[JStephen]

"Question: Is it permissible to install stiffening rings on cone roof tanks to maintain the roundness, peaking, and banding requirements set forth in Section 5?
"Answer: No."
This is an interpretation of November 9, 1994, for the 9th Edition of API-650, published in "Answers to Technical Inquiries" in 1997.
It references Section 5, which has since been renumbered to Section 7.

 

[Eduardo1982]

Thanks guys.. this info was really so important... I was guessing that it could be forbidden. I think that these plates can affect directly the life time of the tank.. Do you know if are there any article that talks about this kind of problems or issues and treats this topic deeply?.. I really appreciate your answers!

 

[Dhurjati Sen]

Be firm, tell your boss about the relevant interpretations and close the topic. No need to dig further.

DHURJATI SEN
Kolkata, India

 

[HTURKAK]

Dhurjati Sen ; Good respond a pink star for you !..

 

[Dhurjati Sen]

Thanks for the star, HTURKAK Sir !

DHURJATI SEN
Kolkata, India

 

[Eduardo1982]

As JStephen said..
"Question: Is it permissible to install stiffening rings on cone roof tanks to maintain the roundness, peaking, and banding requirements set forth in Section 5?
"Answer: No."
But my point is.. what happens when we have umbrella roof instead of cone roof type?.. In my opinion must apply the same concept but the contractor needs something explicit and specific to apply. Do you guys know something a specific section of API 650 what talks about it?

 

[HTURKAK]

Let me correct with layman's terms;

"Question: Is it permissible to install stiffening rings on FIXED ROOF tanks to maintain the roundness, peaking, and banding requirements set forth in Section 5?

"Answer: NO!!!!!."

Does this post answer to your question?..If not, ask the same query to API 650 committee for umbrella roof..

 

[IFRs]

For a new tank, the answer would be stiffeners are not allowed for this purpose. The contract with the tank builder should be reviewed and if it is clear that they owe the owner an API 650 tank then the owner is well within their rights to insist on the contract terms. The owner is entitled to a properly designed, fabricated and erected tank that meets the tolerances of API 650. The quality of the raw material, shop fabrication and the skills of the erection crew should be enough to make a round tank. The vendor is responsible to honor the terms of the contract and comply with API 650.

If after careful and in-depth review you have absolutely no choice, my suggestion would be to remove the stiffeners from the inside, smooth the attachment areas, test via magnetic particle. Then measure the deviations in those areas before, during and after the hydrotest.

If the tank remains out of API 650 tolerance you have to decide if it really matters to you. If after thorough review of design, operations, maintenance and performance expectations it does matter, add seal welded stiffeners to the outside of the tank where they can be observed over time.

Be aware that as the tank is filled it changes shape and as it does this there will be restraint at the stiffeners which means there will be stress concentrations, especially where the stiffeners end. I would not put stiffeners in the bottom course because the bottom course changes shape the most from hydrostatic pressure. Upper shell courses may change shape from wind. All courses may change shape from foundation settlement over time, seismic events, etc.

If attempted, this whole process should be defined, refined and agreed to by all parties in writing, with present and future (warranty) costs addressed and agreed. There needs to be careful thought into why the deviation matters and if adding stiffeners does more harm than good.