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### Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Wed Nov 09, 2016 1:07 pm
A compressed air tank exploded under the deck of a Boston Whaler boat yesterday. The news article explains that compressed air was being used to pressure test the fuel tank. I wonder at what air pressure does the factory normally test the fuel system at? https://goo.gl/zW8V4k

The local NBC news affiliate also covered the story via helicopter, from the video the boat seems to be one of the larger Outrages with triple mercury outboards: http://www.wesh.com/article/boat-explod ... er/8260016

### Re: Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Wed Nov 09, 2016 1:50 pm
The television report of "breaking news" gets almost everything wrong about this incident and has just about zero information value--more or less typical of the usual no-information but sensationalized television news approach.

The other print-journalist story is much more accurate. I highly recommend that link as a source of information. See

https://goo.gl/zW8V4k

There is no mystery about what happened. A large-volume aluminum fuel tank on a boat was over-pressurized with compressed air, probably during a leak test.

The force that can be exerted by a slight pressurization of a fuel tank with compressed air can be significant. For example, if the boat has a rectangular fuel tank with dimensions of 4-feet x 6-feet x 2-feet, that means there is a surface area of three sets of sides:

2 x 4-foot x 6-foot = 48-foot^2
2 x 2-foot x 6-foot = 24-foot^2
2 x 2-foot x 4-foot = 16-foot^2
Total area = 88-foot^2

In terms of inch^2 that is an area of 88-foot^2 x 144-inch^2/1-foot^2 = 12672-inch^2

If the internal pressure of the tank is raised to 10-PSI, this exerts a force on the tank of 126,720-lbs. You can see how a tank might rupture (violently) with that kind of force applied to it.

While the term "explosion" is used, I don't get the impression there was an explosion as a result of very rapid combustion. I think the tank just ruptured when too much force was exerted on it, and apparently the rupture was sudden and perhaps violent.

### Re: Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Thu Nov 10, 2016 11:45 am
When I had a tank built for my 15 center console, it was labeled as having been pressure tested to 2 psi.

### Re: Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Thu Nov 10, 2016 12:43 pm
jihm,

Saying a tank (pressure vessel) is under a force of 126,720 lbsf is a bit mis-leading. It's not mathematically wrong, but only part of the engineering/materials concerns. (Saying a tank/pressure vessel under load of 10 psi is much more appropriate.) -- This is like me saying I am under a force of ~43,500 lbsf at this exact moment, and anyone reading this is also under about ~43,000 lbsf (unless you are in space or deep under water). Or saying your generic aluminum 80ft^3 scuba tank is under ~1,500,000 lbsf while it's on your back before you get in the water... These numbers aren't wrong, but a small part of the equation in determining what is going on materially and structurally.

### Re: Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Thu Nov 10, 2016 4:05 pm
Taking the area of the fuel tank internal surface and multiplying by the force per unit area applied is a good indication of the total force acting on the material. If all of that force is released in a short period of time, the amount of WORK produced can be significant. I don't think most boaters realize how much force is involved to create that much pressure over a large area like the internal surface of a fuel tank.

It would be interesting to know more about where the fuel tank material (aluminum welded plate, I assume) yielded. Did it yield at a weld? Did a fitting yield?

### Re: Boat Fuel Tank Ruptures During Testing at Boston Whaler plant in Edgewater

Posted: Fri Nov 11, 2016 12:25 pm
The leak checks on the tanks are tested at either 2.5 or 3.5 psi for about a half hour. The welds on the tank held, the sheet metal sheared. This happened on a 350 outrage.