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Issues - Hydro-testing of internal floating roof

Wednesday, November 22, 2017   By: MPS [622] 2 Stars

We have an internal floating roof tank with an aluminum internal floating roof and other MOC of tank being CS. Does anyone of you anticipated any issues if hydro-testing the tanks with water if water will be in the tanks longer than 3 days? Have ever you faced Galvanic Corrosion will be caused by using Aluminum Internal Floating roof and hydro-testing with water for periods of time that exceed 3 days. As our tank will take approximately 9-11 days to hydro-test, hold 24 hours and then drain.

Please let us know your opinions.

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Wednesday, November 22, 2017   By: Dunedin [37] 4 Stars
There are too many problems when hydrotesting a tank fitted with an aluminum IFR. You have to remember that all aluminum IFRs have been designed for operation in tanks containing hydrocarbon liquids - not water and this includes water treated with corrosion resistant chemicals. Therefore no matter how quickly you intend to carry out the hydrotest you must be prepared to accept that there will be issues. My advice is that you should hydrotested the tank before installing the IFR.

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Thursday, November 23, 2017   By: MPS [622] 2 Stars
Thanks Dunedin for your quick reply.

However, how the IFR can be installed after the hydro testing of the tank. Our tank have the hydrotest pressure of around 0.6 psig. In API 650, AL.7.5 gives the minimum requirement for quality of test water. But still, API 650 is silent on Galvanic corrosion issue. API 650 talks about pitting, cracking & rusting only.

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Thursday, November 23, 2017   By: Dunedin [37] 4 Stars
You are mixing up two separate issues - hydrotest of the tank and testing of the IFR.

First you have to hydrotest the tank in accordance with the relevant design codes for the tank and its foundation - in my view before installation of the IFR.

Second after hydrotest of the tank and its foundation you may want to check that the IFR will function as intended. This can be carried out using water to check floatation but this should take no more than a couple of hours and any possible damage to the IFR including the seals is kept to a minimum. Or you can test using product.

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Thursday, November 23, 2017   By: DavidR@Fast.net [39] 5 Stars
API 650 new tanks says that aluminum IFRs can be float tested on water or product.
Further, API 650 also has information on the quality of the water used. In my experience, hydrotesting an aluminum IFR is not that bad and has been done thousands of times without issues. Occasionally there is a corrosion issue but I find that following API recommendations takes care of it. Full contact IFRs may be better. Using marine grade aluminum further removes risk, there is at least one vendor that uses these grades for this reason. I just walked on two IFRs in hydro, one came out after a month on water with no issues. Summary: manage the water quality, follow API 650 and you should be OK.

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Thursday, November 23, 2017   By: ITS [1678] 4 Stars
I concur, and wish to add that in order for galvanic corrosion to take place there must be dissimilar metals or metals that have a differing voltage potential in presence of an electrolyte like possibly your water. So, water quality is worth considering. But, I dont see how a few days are going to compromise the passive aluminum oxide coating.

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Saturday, November 25, 2017   By: karsadi [652] 4 Stars
If the IFR has to be tested, what happens if it is firstly added by inserting into the tank with hydrocarbon liquid, for example diesel or some other type with thickness of approximately 20 cm or more, with the aim of a liquid layer avoiding direct contact between aluminum IFR with hydro test water.
How does it make sense or do you agree or any other consequences to avoid? Do you think this way to solve the problem?
Best regards

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Sunday, November 26, 2017   By: Dunedin [37] 4 Stars
Very interesting idea which I had not thought of before or in fact seen used.

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Monday, November 27, 2017   By: DavidR@Fast.net [39] 5 Stars
This works but contaminates the water and makes disposal an issue. People have suggested vegetable oil, etc to help mitigate this but I dont see widespread use of this method.
Galvanic corrosion is the real concern - as the water evaporates it leaves behind deposits that can become galvanic cells to the aluminum and cause pitting corrosion. Widespread or uniform corrosion is usually less of a concern unless the water is alkaline or otherwise generally deleterious to aluminum.
Again - follow API for water quality and washing the underside quickly after emptying the water from the tank. Also, choose a marine grade full-contact floating roof if possible.
Of course, these are only my observations and comments.

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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