Tank Leak Testing

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.)

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

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

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

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

The Britt's would recommend using a "Torch"

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.

Not over 215 bar-litres it isn't!

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

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.

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 .

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

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.

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.

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.

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

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

All together now:

"There's a hole in my bucket

Dear Liza, dear Liza

A hole in my bucket

Dear Liza

A hole...."

- Anon