13 replies to this topic

[emadreza]

Dear Sirs,
We are working in Plant near Persian gulf where fresh water is more expensive.

Anyone have experience carry out hydrostatic test for storage tank using Sea water? What is the precautions that must be taken to prevent corrosion, and what will be the rate of corrosion if we use sea water instead of freash water?

Detail of the steel tanks:
8 x Gas Condensate Storage Tanks 76M dia x 20m
The tank construction material will be carbon steel.

Contractor has a plan to carriy out the hydrostatic test with sea water which may be very corrosive and we can't accept it unless they can prove there is no risk of corrosion to the tanks.

kindly advise.
with best regards

[fallah]

emadreza,

Storage tanks may subject to hydrotest with sea water, provided that the water temperature wouldn't exceed, let say 25C, and there are facilities for rinsing with treated water after the draining of the tank.
A short time exposure of carbon steel to sea water with high chlorides at relatively low temperature, will not result in material corrosion.

Fallah

[Rahimzadeh]

Dear emadreza:
I must add the mr. fallah comment that some times corrosion inhibitor added to seawater for prevention possible corrosion.
M.R.RAHIMZADEH

[Anand K Ramalingam]

Mr Emadreza,

I completely agree with Mr. Rahim, Corrosion inhibitors would certainly help. You have not mentioned whether your tank bottoms (up to 2.0 mts) have any special coating. If they are coated (normally epoxy coated) for crude oil handling, the corrosion issues may not be there especially when the temperatures are at ambient levels.

K R Anand

[Qalander (Chem)]

Dear Emadreza Assalamo Alaikum,.Kindly be careful on few accounts

• Corrosion partially discussed above for Carbon Steel,however if the internal floating roof or screens or some instruments or valves etc. are present within the system which may be heavily corroded or damaged with sea water contact must be taken care off or refer manufacturer's recommendations.
• Moreover a serious hazard is hydrostatic column head pressure increase i.e. gravity increased from fresh water and at times storage tanks do leak and area flooding/possible accidental damage is experienced while approaching desired upper heights up to the brim.

Since most usually the cost is the dictating factor therefore be careful in saving the whole system with additional care on the above points to successfully have the hydrostatic test completed of your tanks in question.
Wish you best of luck

[indiana]

Mr Emadreza,

Kindly take into account the following.

1. You have not mentioned whether the tanks are fixed or floating roof type. There are chances of sea water ingress between the overlap zone of roof plates(~5t width,t=plate thickness) from underside, as they are generally welded from the top side and stitch welded from underside. This is an ideal site for future crevice corrosion and 100% of ingressed water will come out.

2. In case of any austenitic Stainless Steel internals, they may be subjected to Cl-SCC.

Regards,

[indiana]

Mr.Emadreza,

I would like to correct the last sentence of the first point, i.e, it will be "100% of the ingressed sea water inside the lap joint crevice will not come out".

The typographical error is regretted.

Regards,
Indiana.

[Hyper]

Dear All
i think you can not change your test water in this step.because in the detail design you consider special gravity of water in shell thickness calculation.
at this time, if you change type of test water, you should change its special gravity too.

for example;
in detail design you consider water with special gravity of 1 kg/m3 and then you calculate your shell thickness(test condition) in this formula:
4.9*D*(H-0.3)*G / S
which D is Diameter,H is Design Liquid Level, G is Special Gravity & S is Allowable stress for hydro test condition of shell material(e.g. A-516-70)

now if you change G to sea water(in persian gulf, we consider special gravity of sea water equal to 1.023 kg/m3), your shell thickness will be greater.

this matter should be checked first.
maybe there is no problem in shell thickness, because designers shall round up their calculated resulats.(When you calculate shell with G=1kg/m3, maybe resulats e.g 33.26 mm but actually it will be considered as 34 mm also When you calculate shell with G=1.023 kg/m3, maybe resulats e.g 33.95 mm and again actually it will be considered as 34 mm).

if your shell material is A 516 Gr. 70, your first course with G=1kh/m3 is 34 mm but with G=1.023 KG/M3 it will be 35 mm

Also change of special gravity affects on seismic calculation but its not attensionable and its ignorable.

If this matter was ok, dont worry about corrosion.

Best Regards,
Mahmoud

[kkala]

Not having experience with hydrostatic tests using sea water, I know that in local refineries switching from mild water to sea water for fire fighting is acceptable. Of course washing with mild water has to take place after the fire.
It is usual to have mild water storage for about two hours of firefighting, then switch to sea water if needed.
This practice favors use of sea water for hydrostatic test, complying in general with several posts above.
On the other hand sea water seems improper for hydrostatic test of natural gas pipelines (steel, underground), at least according to what is applied here. I remember the commissioning team searching for raw water with quite low chloride content for such a test . Any explanation advice on this (contradiction?) would be welcomed. Of course water is under pressure for the hydrostatic test of gas pipeline.

Edited by kkala, 29 April 2012 - 05:07 AM.

[Qalander (Chem)]

Dear kostas Hello/Good evening,
Actually I have not experienced anything to contradict your comments.
However since the topic was Storage tank specific I shared personal experience overall managing of various works at previous employer's marine terminal and news of happening at nearby terminals witnessed subsequently.
this was the reason I raised caution in response to the OP's query.
Thanks very much you are among the Cheresources 'great contributing individuals' nowadays. keep it up!

However I have somewhat slipped away to some extent,feel sorry for less contribution.

[Qalander (Chem)]

Dear All
i think you can not change your test water in this step.because in the detail design you consider special gravity of water in shell thickness calculation.
at this time, if you change type of test water, you should change its special gravity too.

for example;
in detail design you consider water with special gravity of 1 kg/m3 and then you calculate your shell thickness(test condition) in this formula:
4.9*D*(H-0.3)*G / S
which D is Diameter,H is Design Liquid Level, G is Special Gravity & S is Allowable stress for hydro test condition of shell material(e.g. A-516-70)

now if you change G to sea water(in persian gulf, we consider special gravity of sea water equal to 1.023 kg/m3), your shell thickness will be greater.

this matter should be checked first.
maybe there is no problem in shell thickness, because designers shall round up their calculated resulats.(When you calculate shell with G=1kg/m3, maybe resulats e.g 33.26 mm but actually it will be considered as 34 mm also When you calculate shell with G=1.023 kg/m3, maybe resulats e.g 33.95 mm and again actually it will be considered as 34 mm).

if your shell material is A 516 Gr. 70, your first course with G=1kh/m3 is 34 mm but with G=1.023 KG/M3 it will be 35 mm

Also change of special gravity affects on seismic calculation but its not attensionable and its ignorable.

If this matter was ok, dont worry about corrosion.

Best Regards,
Mahmoud

Dear Mahmoud, I suggest You should recheck the Water density quoted,this seems incorrect it is 1000 Kilogram per cubic meter and a huge error may generate from your values.
Thanks

Edited by Qalander (Chem), 29 April 2012 - 06:47 AM.

[Hyper]

Dear All
i think you can not change your test water in this step.because in the detail design you consider special gravity of water in shell thickness calculation.
at this time, if you change type of test water, you should change its special gravity too.

for example;
in detail design you consider water with special gravity of 1 kg/m3 and then you calculate your shell thickness(test condition) in this formula:
4.9*D*(H-0.3)*G / S
which D is Diameter,H is Design Liquid Level, G is Special Gravity & S is Allowable stress for hydro test condition of shell material(e.g. A-516-70)

now if you change G to sea water(in persian gulf, we consider special gravity of sea water equal to 1.023 kg/m3), your shell thickness will be greater.

this matter should be checked first.
maybe there is no problem in shell thickness, because designers shall round up their calculated resulats.(When you calculate shell with G=1kg/m3, maybe resulats e.g 33.26 mm but actually it will be considered as 34 mm also When you calculate shell with G=1.023 kg/m3, maybe resulats e.g 33.95 mm and again actually it will be considered as 34 mm).

if your shell material is A 516 Gr. 70, your first course with G=1kh/m3 is 34 mm but with G=1.023 KG/M3 it will be 35 mm

Also change of special gravity affects on seismic calculation but its not attensionable and its ignorable.

If this matter was ok, dont worry about corrosion.

Best Regards,
Mahmoud

Dear Mahmoud, I suggest You should recheck the Water density quoted,this seems incorrect it is 1000 Kilogram per cubic meter and a huge error may generate from your values.
Thanks

Dear Sir,
1000 Kilogram per cubic meter is for distilled water and its not economical to use large amount of distilled water for hydro test.
So, usually it shall be considered 1023 or 1025 for sea water.
its depended to nearest sea.

finally we can choose water with any special gravity but we dont forget 2 points;
1- it shall be economical
2- it shall be specified during detail design and parallel to selection of shell plate & seismic design.

Thanks,
Hyper

[Qalander (Chem)]

Sorry dear you still fail to realize/accept and rectify your mistake, let me reproduce from your post
Quote
now if you change G to sea water(in persian gulf, we consider special gravity of sea water equal to 1.023 kg/m3), your shell thickness will be greater.
Unquote

Now here above and any where else one Cubic meter of water is considered; is almost the same as 1000 Litres or 1000X (1Kg/Litre) or 1000 Kilogram per cubic meter for common water and (1000X typical density value e.g you mentioned above 1.023) this should be taken 1023 Kilo gram per cubic meter.

Hopefully you accept and rectify now.Thanks very much.I do know the difference between distilled water and sea water since year 1968/69.

Edited by Qalander (Chem), 05 May 2012 - 07:39 AM.

[Hyper]

hi

i made a mistake in unit.

in the above mentioned equation, SG shall input in gr/cm3.