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Tank Leak Testing

07/04/2016 1:36 AM

Good day.

We conducted a leak testing of a storage tank, fill the tank with water and soaked the tank for 24 hrs (0 pressure)....the next day, there were no leaks observed...when the tank was filled with gasoline on the following week, a leak was observed on one of the nozzle reinforcing pad. How can that happen?

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#1

Re: Tank leak testing

07/04/2016 1:48 AM

Unless the pad is in perfect contact with the shell, there is a tiny volume between. Maybe some water from the test leaked into that space, but not high enough to reach the weep hole (or wherever the leak finally became apparent). Then the gasoline filled the space higher. (That's one idea, anyway.)

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#2

Re: Tank leak testing

07/04/2016 4:37 AM

Viscosity of gasoline is lower than that of water, so if it's borderline maybe gas will leak but not water. Also perhaps the water was making its way to the surface, and if you'd left the test on for a few days more it would have shown.

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#3

Re: Tank leak testing

07/04/2016 5:57 AM
Gasoline0.006
Water0.01

Check the above viscosity chart. (Poise)

You should have known this!

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#4

Re: Tank leak testing

07/04/2016 9:56 AM

Just drain the tank and fix the leak. How it happened is irrelevant.

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#6
In reply to #4

Re: Tank leak testing

07/04/2016 11:05 AM

Drain the tank???? That'll take too long.

Use this stuff. It's guaranteed.

Flex Seal ® Black ‑ Liquid ... $14.99 Flex Seal Pro...

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#20
In reply to #6

Re: Tank leak testing

07/05/2016 8:04 PM

A match is much more expedient, you know...

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#21
In reply to #20

Re: Tank leak testing

07/05/2016 8:29 PM

Certainly a match would be called for if the repair is made after dark.

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#26
In reply to #21

Re: Tank leak testing

07/06/2016 6:44 PM

The Britt's would recommend using a "Torch"

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#15
In reply to #4

Re: Tank leak testing

07/05/2016 8:16 AM

Uhhhhh, might want to be sure all vapors are gone before welding, and just filling with water may not be enough. Just a thought, knowing what happened to 2 friends in the oil field who tried to weld their gas tank for an old cable tool rig.

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#19
In reply to #4

Re: Tank leak testing

07/05/2016 12:51 PM

To many of us, the why of something is all we ever think about.

Answering the "why" is essential to understanding, understanding is vital to good design.

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#5

Re: Tank leak testing

07/04/2016 10:36 AM

Whatever was plugging the leak the first time is soluble in gasoline. Gasoline dissolves many nonpolar substances that are insoluble in water.

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#7

Re: Tank leak testing

07/04/2016 3:18 PM

An air test would have been more appropriate.

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#8
In reply to #7

Re: Tank leak testing

07/04/2016 3:49 PM

Not over 215 bar-litres it isn't!

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#28
In reply to #7

Re: Tank leak testing

07/10/2016 8:15 PM

And dangerous.

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#9

Re: Tank leak testing

07/04/2016 3:51 PM

Another possibility is that the wrong materials have been selected for the tank structure.

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#10

Re: Tank Leak Testing

07/05/2016 12:00 AM

Two different types of lliquid.

Water, due to surface tension, "resists" passing through quite small holes, that other liquids can flow through easily...

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#11

Re: Tank Leak Testing

07/05/2016 1:36 AM

You have a leak on the tank to nozzle weld, the reinforcing ring must be removed and the weld repaired under it. Then the reinforcing pad can be reinstalled.

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#12

Re: Tank Leak Testing

07/05/2016 3:13 AM

I think Gasoline evaporated and increased the pressure in the tank. So additional to the lower viscosity issue the pressure in the tank increased and that leaded to the leakage. A Gasoline tank will have to be closed up hermetically to avoid the Gasoline vapor to escape. With exposure to the sun the pressure increases further.

So a leaking test even with water should be done with an hermetical closed tank and increased pressure. The applied pressure should be as high as the vapor pressure of the liquid to be stored in the tank.

Interesting example was our car in Singapore - we did not notice that the petrol pump didn't work as the car was parked outdoors in the sun and we could move around 10 to 15 km with the gasoline vapor pressure in the tank. Only when we were driving longer distances the car would sputter and shake - when I investigated the reason for that effect with the car standing for some time - it would again run perfectly - as there was enough time for the vapor pressure build up - which send gasoline to the carburetor again.

So after I understood the reason I could travel to the repair shop 30km away by going shopping 2 times just to wait for the vapor pressure build up. A new petrol pump fixed the problem.

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#13

Re: Tank Leak Testing

07/05/2016 5:41 AM

I don't know where you are but testing a gasoline tank with water at atmospheric pressure violates so many codes in most countries in the world that you may as well not of bothered doing the test. You were certainly not in a position to issue a test certificate as proved by the subsequent leak. Without a valid test certificate no insurer will pay out in the event of a claim and would probably not underwrite insurance in the first place.

Without a test certificate and insurance you are probably using the tank illegally.

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#14

Re: Tank Leak Testing

07/05/2016 6:18 AM

Liquids have a vast array of characteristics . The differences between H2O and gasoline are great . Your test would have worked on a large leak , but smaller ones , especially with obstructions , the variables make testing with two different liquids a highly inaccurate method of testing .

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#16

Re: Tank Leak Testing

07/05/2016 9:17 AM

In addition to the viscosity difference mentioned, you should have applied pressure to the tank and watched for a while.

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#17

Re: Tank Leak Testing

07/05/2016 9:30 AM

Had you used ultrasonic leak testing based on my experience the leak point would have been obvious. Check out SDT and UE for information on this type of diagnosing. You will probably spend the cost of this equipment on the draining and flush and repair unless the suggestion by Lyn works.

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#18

Re: Tank Leak Testing

07/05/2016 10:20 AM

Please describe where do you observed the leaks?

1. If it is from the weep hole which you used for the air testing the welds at pad periphery and nozzle neck periphery than there is a crack developed in weld between nozzle and shell inside shell. There is no way to repair externally but emptying the tank and fix the weld. The wax you plug the hole with is dissolved with gasoline.

2. If leak is at nozzle neck you got lot of problem.

3. Do you have any bolted connection on this nozzle inside the tank? If yes than the gasket joint may leak inside nozzle pipe some time.

4. I have seen one cycle is enough to develop a crack in fillet weld which may allow the gasoline to leak through. I have recently seen the nozzle which was flush inside and no weld of any kind inside the shell.

5. One way or other you got problem with bad weld, improper testing and lack of inspection by quality.

6. I think API allows diesel as penetrant because lighter product like diesel and gasoline can penetrate thorough hair line crack.

GOOD LUCK.......

P.S. Long time ago when first Tank Industry Started inspection program one of my boss got sprayed with crude on his face when he took the plug out of weep hole. I stayed away from Tank Inspection.

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#22

Re: Tank Leak Testing

07/05/2016 10:49 PM

Apart from any possible pressure buildup, gasoline and water have different surface and interfacial tensions. Meaning that the gasoline may have wet through a crack that the water did not, especially if the leak was observed a while after filling.

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#23

Re: Tank Leak Testing

07/06/2016 9:18 AM

Did you performed pneumatic tests to nozzles reinforcements before the leak test as is set in all codes related to tanks storage erection?

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#24

Re: Tank Leak Testing

07/06/2016 10:38 AM

23 posts, having four mentions of "viscosity", prompts me to add the following.

IF the tank had received the full-gamut of nondestructive examinations, including weld integrity checks, it MIGHT have undergone dye penetrant inspection of those welds.

[let me also add, before continuing, that as inspectorjoe, the OP, failed to include any details whatsoever, there's been a lot of *assuming* taking place thus far]

IF the penetrant examination was performed properly, any welds that were on the verge of failing would probably have been revealed.

Interestingly, in the case of this type of test, viscosity (of the test fluid/penetrant) does not play a central role. Capillary action and the contact angle (wetting ability) of the penetrant are the key players.

And, whereas water makes a poor penetrant (as already insinuated), molasses exhibits good penetrability (as well as being deadly).

Just my two cents worth ~ (wonder if we'll ever hear from the OP again?)

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#25
In reply to #24

Re: Tank Leak Testing

07/06/2016 4:34 PM

Good post, and thanks for the molasses flood link. I had no idea!

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#27

Re: Tank Leak Testing

07/07/2016 6:26 AM

All together now:

"There's a hole in my bucket

Dear Liza, dear Liza

A hole in my bucket

Dear Liza

A hole...."

- Anon

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