Fuel Tank Demolition Advice Needed

[jibes138]

I emptied my diesel tank last year and because it can't be removed intact I left it in place and installed a small 6 gallon tank in order to use the boat through storm season. I talked to a mechanic who was considering cutting it up in place but felt he would have to fill the tank with nitrogen to prevent potential explosion hazard from sparks and residual fumes.
My question to the group is could a tool like a fein or equivalent like a rockwell with a metal cutting blade be used to make cuts in the tank to remove it in pieces? I've never worked with a Fein but it looks somewhat like a hacksaw blade with really fine teeth. Would it cut fast enough or take forever given the amount of cutting. If I cut the tank in half horizontally i can easily get each half out. Do I need to worry about fire using a Fein and what would you suggest to minimize the risk? Since the tank was seeping using liquid nitrogen would spill liquid nitrogen all over the boat and in the bilge something i don't want to do. I could fill the tank with water but would have 30 gallons of contaminated water to dispose of. Could I discharge a fire extinguisher in the tank and would that provide protection? How about running a blower through the fill tube to prevent any residual fumes from accumulating?
Any thoughts most appreciated.

 

[Stu Jackson]

Dave, early morning thoughts:

--- diesel isn't too sparky - famous last words, right? But certainly not like gas.

--- the tank has holes, so anything you try to put into it is gonna come out

--- can you remove your fuel tank sender? That'd put a big "breather" hole on the top.

--- only you can tell the geometry of what's there, so I don't think any of us could tell you how to get it out.

--- If you can temporarily plug the holes, have you considered dumping some water into the tank and removing it with a pump of some sort. That'd get rid of what little fuel you may still have inside. You could use absorbent pads around the tank and in the bilge.

--- Have you considered an "extension" of your day tank approach by not reinstalling a tank in that location? Is there anywhere else you can put a tank, maybe even a second smaller tank?

 

[damauney]

Dave
Did this on my O35 and replaced it with a florida marine tank 20 gal with the same configuration but shorter. You are welcome to drawing and tank cradle drawing. Emptied tank through Gage hole with hand pump. Pushed air through it out inlet for a month with a 12 volt muffin fan for a month. Now dried out I cut it up in place with a sawsall. Went well. Good thing about aluminum is it doesn't spark. Only pain was around baffle but doable. Sailing Cal was helpful with pictures.

Goodwinds
DaveM

 

[damauney]

Opps

 

[RichH]

Safest way to cut up the tank is to fill with water and use (rent) an impact air chisel with a special 'sheet metal peeling blade' .... essentially a flat blade with a small 'hook' which does the cutting. Use water soaked turkish towels to apply to keep the 'heat' reduced on the cuts so that any fuel still remaining on the walls remains below its 'flash' point. Work slow so that the heat of cutting doesnt become excessive. Simply take your time when cutting so that heat of cutting is able to 'dissipate'.
To help control the hazard, spread heavy duty liquid 'garage type' floor cleaner onto the inner surfaces of the tank and let dry, remove the cleaner and soaked oil if you have access and recoat the walls, etc. Be sure that the 'cleaner' is not flammable by itself. If you cut a large access hole in the tank top, then you can consider to manually clean out the inside of the remaining tank top for added safety, then refill with water.

If this is a gasoline tank .... 'very dangerous to cut up' because of explosion risk.

The use of nitrogen can be dangerous as when the N2 'spills' out of the tank when you make the cuts, the N2 can 'displace' the ambient air ... and you will/can instantly die of asphyxia. Nitrogen asphyxiation is what killed 3 astronauts during the early Apollo Program when nitrogen was released into the crew cabin to suppress a small fire.
There are nitrogen or inert gas filled 'foams' to do this 'blanketing', the 'bubbles' contain the nitrogen, etc. and prevent and lessen release of the N2 into the surrounding atmosphere - contact a local specialty welding shop who specializes 'tank work' for the petro-chem industry, for availability.

 

[jibes138]

DaveM...thanks, that's exactly what I had in mind. The same tank configuration but shorter so it will fit in without boat surgery. 20 Gals is plenty of capacity for most usage. I emptied the tank through the gage hole so it is empty but may have some residual fuel and crud in it. The fan idea is a good one. I was thinking of maybe a hose to the fill tube connected to a squirrel cage fan with some plastic and duct tape. Should blow a lot of air through it.
Sawzall should do the trick, did you pull it out over the stuffing box for easy access before the cutting process? I was thinking of laying a sheet of plywood across the quarter berth and cockpit locker to rest it on while I hack it up.

Stu, thanks for the response. I like the location since it is on center line. Your idea of inject some water and pump it again to get rid of residual fuel is good. Since the fuel floats if I skim the surface first it should pull out most of what's left. I could probably just have maybe 5 gallons to dispose of. I think the risk is low but wondered what others had done and I'd prefer zero risk.

What are your thoughts on a Fein versus a Sawzall? Would a Fein take forever in your opinions?

 

[damauney]

Dave

Sawsall really did the trick. Cut the top off down about 6" and pulled the rest out through the quarter berth. I will post drawings and pictures this evening. I thought about soap but more contaminated stuff I had to get rid of. As it ended up with constant slow air movement for a month hardly a diesel smell and crud was cracked up like clay in dry river bed.

Goodwinds
DaveM

 

[25yearslater]

Anchor chain and 3/4 inch steel bar. Loop chain around tank and insert bar. Wind it like a model airplane rubber band. I can try this tomorrow on my old steel tank if you would like? Another option is to warm the tank with an electric heater, cap it and pack in ice. Differential pressure may crush it flat. Or some combination of both.

 

[Tom Potter]

jibes are you thinking of repairing the tank when removed?

Something to think about, I pulled the tank from my O28 this summer. The bottom inch or 2 was bad and had a small leak. The rest of the tank was in great shape. I found a local guy that does metal work, he cut the bottom 3 inches off the tank and welded on a new bottom, pressure checked and shortened the fuel pick up tube. I recall all less than $150 much cheaper than a new tank.

 

[jibes138]

Tom,
The problem I have is the tank won't fit out through the quarter berth or through the cockpit locker. Unless I pull the engine the only way to get it out is to cut it in half, or do as Sailing Cal did and cut the side of the quarter berth larger to make enough room. I plan to cut it in half as DaveM in Oriental did and then install a shorter tank so it will fit in. DaveM had a 20 galllon tank built, should be plenty of capacity. The company that made the original tank is located in NC and still in business. So I figure they can make me a new one to the same dimensions just shorter. Thanks for the input, I remember reading about your repair, it was a good idea.
Are you using fiberglass backing plates for your through hulls? MaineSail had a nice article on his website about that instead of plywood. Also suggest you use real seacocks instead of the O'Day original equipment he had a great article on that also. My next haulout I will be doing the same with my seacocks.

 

[SailingCal21]

Just do what I did and cut the damn fiberglass and pull the sucker out. You can glue the glass back (just make a cleaner cut than I did), put some trim over the repair, then go to the next project.

Trust me, the cut will only be noticed by you.

 

[SailingCal21]

jibes are you thinking of repairing the tank when removed?

Something to think about, I pulled the tank from my O28 this summer. The bottom inch or 2 was bad and had a small leak. The rest of the tank was in great shape. I found a local guy that does metal work, he cut the bottom 3 inches off the tank and welded on a new bottom, pressure checked and shortened the fuel pick up tube. I recall all less than $150 much cheaper than a new tank.

Jibes,

I've still got my old tank, you are certainly welcome to it if you want to go this route.

 

[damauney]

Replacing O'Day 35 Fuel Tank with 20 Gal Tank

I have attached some pictures and drawings of my replacement of the 30gal tank with a 20gal tank so I could get more battery room.

Goodwinds
DaveM

 

[SailingCal21]

I have attached some pictures and drawings of my replacement of the 30gal tank with a 20gal tank so I could get more battery room.

Goodwinds
DaveM

Most excellent work. I should of considered a smaller tank as did you. You actually have an inspection/clean out port!

 

[damauney]

Sailing Cal

Your work got me going this way. Really appreciate it.

Goodwinds
DaveM