Oil Tank Failure

[SteveGregory]

I looked at a 275 gal. residential oil tank that ruptured while it was being filled. The tank had 50 gal. and the oil company said it stopped after pumping 135 gal in about 10 minutes.

There was separate vent pipe in the center of the tank. It broke along a welded seam at the end of the tank. I heard claims that the tank broke from "being filled too fast" or "excessive pressure built up inside". Could these claims be true? Why or why not?

 

[jte]

Is the centerline of the tank vertical or horizontal? How is the vent pipe attached, how is it supported, what is its diameter, was it plugged? Who checked the pipe to ensure that an old wasp nest wasn't plugging it? How was the vent pipe welded to the head - set in and double fillet, set on and single fillet, or full penetration? Any reinforcing pad?

Breaking a circumferential seam due to overpressure is not highly likely. The stresses just don't exist - you'd see a longitudinal seam failure first. And even a small diameter vent pipe would handle 15 gpm vapor flow. I would take a very close look at the fracture surface with a suspicion towards fatigue. Any rust on the surface with a relatively small shiny part (which may indicate a progressive failure)? Did it break at the weld, HAZ, or base metal?

jt

 

[MJCronin]

jte is correct.....the vent pipe was plugged

.. and the bird that was trying to build a nest in the pipe has been drilled into the ground.

Pressurizing anew tank, you simply cannot build enough backpressure in the vent pipe to cause rupture.....the tank fails first. It is the "weakest link"

How old was this beast ? 15 - 20- 30 years old !!??

Are we discussing the failure of layers of rust ?

- MJC

 

[SteveGregory]

The tank was 38 years old and located in a basement. The vent pipe is a 1" pipe and it was clear.

There was only a very small amount of light surface rust on the exterior of the tank.

 

[jte]

And the answers to the rest of my questions?

 

[SteveGregory]

The broken seam is on the end of the vertical tank about 15" from the bottom. I think the attached pictures should answer your other questions.

 

[MJCronin]

My vote...

No bird...(bugs...perhaps..?)

The 38 year old tank finally gave out (for any number of reasons, nothing lasts forever)....

When the tank seam burst, the tank moved enough to shear off the vent...

This is borrrrrrrring

-MJC

 

[SteveGregory]

Well, IMHO (newbie) the tank did not burst because of pressure buildup - the 1" vent was clear and the delivery was between 10-20 gpm.

The owner wants to sue his Homeowner's Insurance carrier for the oil mess in his basement from his old tank. I think it was just old and past its useful normal lifespan and the oil found a weak spot. Can you support my argument or dispute it?

 

[jte]

The photos are not sufficient to document the failure. Photo 001 seems to show a longitudinal seam which fishmouthed open. But I could be totally misinterpreting that. If it was just plain old corroded out, we'd see a weeping pinhole leak somewhere. The appearance of a fishmouth implies some force to move the steel and that implies pressure.

What/how would you define "useful normal lifespan"? There's more to this than we're seeing. At what temperature did the failure occur?

jt

 

[786392]

Just a wild thought,

If no flame arrestors on the 1" vent(as probably is the case here)somehow air got sucked-in& envisage some sort of explosion/implosion like phenomenon as taking place!

Other forum colleagues may enlighten us!

Best Regards
Qalander(Chem)

 

[SteveGregory]

jte, I am guessing that it was a cool day. It was in February.
I would like to find some documentation from the Steel Tank Institute on what the normal useful life of these tanks are. If there are any members here that could post that document, I would appreciate it.
As far as I know, there were no leaks prior to the rupture. The fishmouth is troubling since it doesn't seem like any significant pressure could have built up in the tank.
Just speculating... perhaps the tank was damaged (kinked) IF it was relocated or moved to the basement. The damaged area provided a weak spot for the seam to rupture.

 

[jte]

Steve-

The fracture surface should be looked at by a competent materials engineer/lab. I'm not... so I'd ask my colleagues to look for indications of brittle fracture. A tank that old likely didn't use base metals nor welding technology which would provide good toughness. The transition temperature might be a lot higher than you might guess - easily on the order of 70°F. If you can get a coupon cut from the remaining weld, you could get that tested for fracture toughness pretty easily. But... you still need some explaination for what energy was provided to do the work of deforming the steel.

jt

 

[SteveGregory]

jt,
A retired Materials Engineering instructor at a local university said "the fracture surface exhibits a ductile fracture mode". This finding was based on an SEM examination for what thats worth.

 

[jte]

Well, I'd consider that a qualified finding! You are now left with finding the energy source which could cause that deformation.

jt