Pipefitter ....a welding question .

[PeterSibley]

Hello mate . A welding question if I may ? I'd like to use stainless gas cylinders ,ex motor vehicle , as diesel tanks in the boat .Have you welded old gas cylinders , would you ? How about cutting with an abrasive discs ?

I'm scared of them ...is there any safe way to use them .

These cylinders would be very good ,316 stainless, about 30 gallon and well made but they need modification .

[andrewe]

Hi Peter,
I will chip in here, I expect Pipefitter is still snoozing.
I fill them up with water (after washing them out) leaving a small air space at the point I cut or drill. The stink of the gas is an oderant added as most gases have no strong smell. This stink hangs around long after the gas has gone. Aside from eliminating air, drilling into water cools the metal so no hot chips. So far I have only used steel tanks, not s.s. But the same principles apply.
I may put my head below the parapet now,
Andrew

[The Bigfella]

Peter

While waiting for Pipefitter to wake up, here's a couple of shots of the fitting we made for the fuel take-off.

http://i240.photobucket.com/albums/ff112/igatenby/tankfit2.jpg

The O ring is missing from the fitting, but you can see the groove.

http://i240.photobucket.com/albums/ff112/igatenby/tankfit1.jpg

Incidentally - the only cutting we did to these tanks was to take off the excess metal around the hole that these go into, and to drill three holes in for other fittings - the breather tube fitting, a 2" hole for a filler pipe and a hole at the bottom for the drain fitting. We didn't fit a sump because of the round end to the tank - and our drain goes into the low spot. This last fitting is protected by a thick piece of metal that is sufficient to support the whole weight of the full tank - but won't have to given the tank straps.

Here's the overall shot again. I have more photos - but dunno where....

http://i240.photobucket.com/albums/ff112/igatenby/DSC_0009.jpg

[PeterSibley]

Thanks Andrew ,that sounds like the way to go .I can still remember my welding teacher saying NO ,under any circumstances .............but it has to be done .

Ian ,a neat job ! Mine would have to lie horizontally ,so a sump is probably necessary .

I'll wait for the final word from Pipefitter !:)

[The Bigfella]

Mine would have to lie horizontally


you'd need to baffle them too.

[PeterSibley]

Yeah , I know .That's were the cutting disc query comes in .Cut then in half or cut an end off ,weld in baffles , reweld .Cut opening , weld in sump and fittings !

[Gary E]

1... they NEED baffels....those dont, and doubt you will cut them apart to put baffels in

2... ROUND shapes dont hold what rectangular shapes hold...

I'd not use them even if they were FREE... Have proper tanks made to FIT your boat..

and here in the US we need Coast Guard approval of tanks...do you?

[pipefitter]

What kind of 'gas' were they used for? If propane, there is no worries.

First, I am not going to advocate recycling old 'gasoline' tanks. Especially without seeing what the interior condition is. I go through quite a diligent cleaning process before I will attempt it myself and some I reject entirely. I am also equipped to purge tanks with co2 or argon before doing any cutting or welding on them if I feel it necessary.

I've welded on quite a few used aluminum tanks but none of SS. Only time I worry about fire or flash back is if they have a significant buildup of stale gas varnish inside that is still gummy which is no good to be used for a tank anyway unless you want to clean them out which usually requires some perpetual oscillation with a medium such as sharp gravel inside with strong detergent which usually begins to negate the economy of using it in the first place.

I am in complete agreement with Gary about using proper fitted/approved tanks, which I always recommend. Bigfella has the right ideas about sumps and drains. If you are set on using the old tanks, wash them out well with a good detergent first and then set them in the sun for a couple days to dry. Stainless will get hot enough in the sun to vaporize any remaining flammables.

The smell of stale gasoline is my least favorite smell in the world.

By the time you buy the abrasives in which to cut, the material for the baffles and the proper bungs for fittings and your time etc, you are probably half way or better to what it would cost for a proper new tank. Not to mention having pressure test capable welds.

[donald branscom]

Pipefitter may dissagree but...

I would not do this job if asked. No way.
I do not care if they are washed out or not.
First i think making tanks from stainless is a mistake.
There is this mis information that stainless does not rust. WRONG.
It is subjet to crevice corrosion. You cannot detect the corrosion like you can with steel. Aluminum would be better.

I have been asked to weld tanks and was told it was risky. How right the welders that warned me were. Any kind of petroleum product gets into the fabric of the metal and when it is heated up it forms gasses that become explosive.

Let me give you an example.
A man wanted a lawnmore gas tank welded. i washed it out with soap and acetone and washed it with soap and water one final time. Yes three times!

i was welding with a tig torch and had all of the openings open.
It still flashed over after a couple of seconds and made a bang and flames wooshed out of the openings. scared the hell out of me.
A couple of years later i tried one more time. Same result.

I do not think a tank should be welded if it has contained any potentially explosive material. It can get you killed.

Go to any of the welding websites and this subject is discussed a lot.
There is always one out of 10 that say you can do it.
That is because they did it once and got away with it. It is not safe!

[PeterSibley]

OK gentlemen ...good advice .I'll make or have made custom tanks to suit the shape .I'm relieved to be told not to ! I share Donald's horror of exploding tanks !

Ian's advantage was being able to use them as is .

[The Bigfella]

Ian's advantage was being able to use them as is .

Not entirely Peter.... we still had to put the fittings in, and turn up the new covers for the inspection port - and we rolled and welded up new straps, but yes, the basic elements of the tank remained. I would have probably drawn the line at fitting baffles, but as mine are upright ....

What attracted me to these tanks as much as anything was the ability to take them out again if ever needed - the previous tanks setup was 2 x 450 litre rivetted tanks, probably dating back to 1938 - which were a nightmare to remove - days of airchisel, and various other tools, cutting them down to small pieces that would fit out the lazarette hatch.

That and the problems associated with carrying 900 litres of fuel on a boat that does not do long distances. It goes stale - or you keep the tanks less than full and run the risk of condensation. When I pulled the old tanks, there was gallons of "mud" in the bottom - the remains of the algae that feed on the boundary layer between water in the bottom of the tank and the diesel - and I gave away 600- 700 litres of stale diesel that my mechanic said was not worth running through my engines.

Yep - if I'd made square tanks, I could have squeezed another 100 litres or so of fuel in, beyond my 620 litre capacity. But, given that I only plan on using the centre 2 (of 6) tanks, that last 100 litres just isn't needed. IIRC, I used 80 litres last time I took Grantala down to Sydney - back in 2000, for the Olympics - not even half the capacity of the two central tanks - which hold enough for about 150 nautical miles. Any longer trip in this boat will be done in a series of coastal hops - with plenty of fuel available. Filling all six tanks gives a range of about 450 nm.

Donald is right about crevice corrosion of course - which is why these tanks are kept clear of any situation that would lead to it. They do not sit on anything that touches the tank - apart from the piece that protects the drain tube - and it is a non-structural piece.

- oh yeah guys - these are old Propane tanks - no lacquer issues.

[pipefitter]

Pipefitter may dissagree but...

I would not do this job if asked. No way.
I do not care if they are washed out or not.
First i think making tanks from stainless is a mistake.
There is this mis information that stainless does not rust. WRONG.
It is subjet to crevice corrosion. You cannot detect the corrosion like you can with steel. Aluminum would be better.

I have been asked to weld tanks and was told it was risky. How right the welders that warned me were. Any kind of petroleum product gets into the fabric of the metal and when it is heated up it forms gasses that become explosive.

Let me give you an example.
A man wanted a lawnmore gas tank welded. i washed it out with soap and acetone and washed it with soap and water one final time. Yes three times!

i was welding with a tig torch and had all of the openings open.
It still flashed over after a couple of seconds and made a bang and flames wooshed out of the openings. scared the hell out of me.
A couple of years later i tried one more time. Same result.

I do not think a tank should be welded if it has contained any potentially explosive material. It can get you killed.

Go to any of the welding websites and this subject is discussed a lot.
There is always one out of 10 that say you can do it.
That is because they did it once and got away with it. It is not safe!

No, Donald, we are in total agreement. I have welded tanks successfully before but as I said, I have a purge system to deplete the tank of oxygen. As it stands, when the owner takes on these jobs anymore, I tell him I have children and it isn't worth it or I will charge double what a new tank would cost just for the accompanying ulcer and gray hairs. I have welded aluminum tanks successfully but I don't like to.

[pipefitter]

Just so you know that welding on tanks is not foreign to me. Here's one I had to relocate the fittings to be within reach of new gunwale mount fill and starboard side vent.
http://i99.photobucket.com/albums/l309/tigmaster/P2260090.jpg

Plus had to cap the existing fittings.
http://i99.photobucket.com/albums/l309/tigmaster/P2260088.jpg

[Lew Barrett]

I was going to (politely) question the wisdom of multiple round fuel tanks as opposed to fitted tanks but Bigfella actually supplied a logical explanation. I'd still go with bespoke tanks (and did in fact) for maximum capacity and worry free operation in my situation, but I must say your installation looks good Ian.

I wish I'd documented the re-tanking job when we did it (for many reasons one of which will be obvious soon enough) but that was before I realized the value of photographs for future reference and discussion.

[pipefitter]

Seems that every time one of these topics arises, I get summoned to do such a job either during or shortly thereafter. This tank is for a 60ft sport fish. The whole boat is going to be completely rewired and refit mostly by us. Already rebuilt the humongous SS bow rail. Wish I would have taken photos of the purge setup. The thru penetration of the welds on the interior look nearly as sweet as the exterior.

[The Bigfella]

Well, I'm doing another one....

I took an old 80 litre 316 SS LPG tank down to the boat today to do a final check on whether I can get it in / out or not. The answer is yes!

This will be my genset tank and it fits under the galley floor beside the (stainless) water tanks. I cut 2 of the 3 new openings on Monday, but wanted to see what sort of angle I could get the tank up to before putting in the drain pipe. I can only raise one end about 7" - so will have to baffle it....

I filled it with water before cutting into it - and could detect a slight propane smell in the air being displaced - but (given I'm still here) - had no problems cutting it. I've had this tank sitting around in the yard for 4 - 5 years or so with no cap on it, but its only about a 2" port.

I'll refill it before welding it too.