Sea water hydrotest on tanks

[Weko]

Currently we are designing a floating roof tank with the diameter of 80m and height of 20m. Due to the unfeasible source of fresh water, our client premitted us to do hydrotest by using seawater.

Since we are not familiar (experienced) with hydrotesting using seawater. We are still in searching reference for the following:
1. What type of the corrosion inhibitor?
2. Is biocide used also?
3. After hydrotest, we do flushing on the deposit salt. How to ensure the salt are already removed (what are the parameter, how to measure).
4. Is there any othe concern that probabbly I missed?

Thanks..

 

[fegenbush]

You might have missed that seawater has a higher specific gravity than 1.0 (it's about 1.03 last time I looked).

 

[IFRs]

Is this a steel or aluminum floating roof - each has different concerns.
What will the tank be filled with?
How long will the tank stand idle before it is filled?
Is the tank heated?
Seawater is not the same everywhere, it can have a wide variety of chemicals.
I would get the test done quickly, clean the tank and get it into service quickly.

 

[Weko]

The roof will be steel. And will be filled with Naptha. And the tank will not be heated.

We are still developing our project schedule. But I predict probably two weeks or a month before it is filled. Any suggestion so the inside shell of tank will not corrode? Using internal paint linning?

 

[LittleInch]

Testing with seawater is very common for subsea pipeline for the same reasons and hence a great deal of experience has been gained. Search "pipeline seawater inhibitor" on this site and google and floowl a few chemical company links. You really need to talk to a vendor AND which ever authority / environmental authority is going to allow you to dump the seawater back in the sea again for the approved list of chemicals. The further out tio sea and deeper down the better.

Corrosion inhibitor is not effective in this environment.

You normally need clean filtered seawater ( go for min 50 micron) biocide and oxygen scavenger, hence for a tank you might need a nitrogen or CO2 blanket to avoid re-oxygeneation of the seater during test. Make sure as much as possible you are not dragging in silty polluted water.
You probably need to do a tank clean. There are tank cleaners everywhere. You can measure chlorides in the drain water, but really a good fresh water spray should do it.
If you can spray coat the tank with any sort of decent paint so it doens't dissolve in naptha, this would be very beneficial.

So long as your test is quite short and then you evacuate the tank, drain it, clean it and make sure all the small pools on the floor are flushed away with fresh water, you should be Ok.

Remember that the seawater is heavier than fresh water as fegenbush says. This may mean you don't fill the tank right to the top

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MJCronin]

http://cr4.globalspec.com/thread/22470/Hydrostatic-Test-of-Storage-Tank-Using-Sea-Water

 

[MJCronin]

ASM recommends special Zinc-rich Paints.....

http://www.asminternational.org/por...0000701e010aRCRD&campaign=recommends-personal

 

[MJCronin]

Cortec has a proven system....

http://www.cortecvci.com/whats_new/announcements/ch 304.pdf