Stainless steel tanks

[Guest]

I have an Ebbtide 33 (steel) she has a 30 gallon steel tank for kerosene. I am planning to replace this tank with two tanks that will occupy the same location which is high up in the starboard cockpit locker. The new tanks will be a 6 gallon tank for the kerosene and a separate 24 gallon diesel tank to act as a day tank/gravity feed. I am planning to make the new tanks from stainless steel. Does any one have any experience of welding SS tanks. I have a mig welder and have some experience working on mild steel.Should I use SS 316, Is it satisfactory to use anySS welding wire. I have only seen it available at Machine Mart. Where could I obtain all the tank fittings, e.g. pipe adaptors, filling points, access hatches.
P.S. would it be possible to use GRP/epoxy to make the tanks would there be any problems with kerosene or diesel.
P.P.S. The existing diesel tank which is in the keel, will be retained as the main tank.

 

[30boat]

You can use your Mig machine but with Argon gas,do not use Co2 with stainless steel.
The problem with welding thin stainless steel plate is that unless you are able to shield the underside of the weld from the atmosphere the result will be a week crystalised weld.To protect the area to be welded you will have to back gas it with Argon and that means filling the whole tank with it wich apart from the dificulty in getting it right, is expensive.Yes, you should use 316 steel and wire of the same spec.You will also have to deal with distortion. Glass/epoxy is probably a better bet.
Have you tried those plastic injection moulded tanks?I've got one in my boat and it's great.In fact it replaced the old leaky stainless one.

 

[PaulJ]

Unless you are a very accomplished welder and used to welding stainless I would not recommend welding your own tank for all the reasons that 30boat has stated. I too have an Alan Pape steel boat very similar to your Ebbtide and have been having great trouble sealing a minute leak in the welded main tank. I would strongly agree with 30boat , go for a plastic tank and if you can't find a moulded one to fit, give TEK-TANKS a ring (01420 564359). They will makeyou a very strong polysomething tank to whatever shape and size you specify.

 

[charles_reed]

Stainless is a pig to weld - distortion is the big problem, especially with large flat areas, as is getting sufficient penetration without burn, granulation and stress-points.

I'd not attempt without the experience and gear (argon arc).

The wire is the easy part - but you need to be certain you're using A2 with A2 and A4 with A4 316.

The trouble with both diesel and kerosene is that they can find their way through the smallest pinhole - for that reason hand-fabricated composite tanks are suspect.
Why not look at some of the gr polypropylene tanks on the market - you might find one of the range that fits?
Failing that, save yourself the agony and get them made by a specialist - if you're interested I've got someone who makes ss pressure vessels for the process industries and would be more capable than your marine fabricators.

 

[Guest]

I had contemplated doing the same but been put of by complications however I have some budget options to polly tanks. Have you thought of either flexible tanks which seam to work ok or, for desil using mild steel. The desil inhibits corrosion on the inside and hammerite is good on the outside. I have sucessfully made galvanized water tonks and had no problems with leaks though found welding seams inside and out useful.

Roly, Voya Con Dios, Glasson, Lancaster

 

[Guest]

I would like to thank all of the comments so far. My skill with a mig welder is only ok, so you have certainly convinced me not to attempt to weld my own. I now think that I will either go for an epoxy/ GRP tank or a Poly TEC tank.

 

[laffinskip]

on the subject of tanks.could anyone tell me the expected lifespan of a mild steel tank used purely for diesel for the last 30 yrs.
It has never leaked but I feel like a man waiting for a volcanoe to blow. When??? or am I worrying without cause.

 

[vyv_cox]

on the subject of tanks.could anyone tell me the expected lifespan of a mild steel tank used purely for diesel for the last 30 yrs.
It has never leaked but I feel like a man waiting for a volcanoe to blow. When??? or am I worrying without cause.

Corrosion needs water to take place. Provided the tank has been drained regularly to remove condensed water vapour or leakage it will be perfectly OK. Few of us keep the same boat for 30 years, so it seems likely that you don't know this!

I suggest that inspection with the tank drained would relieve your concerns. You can buy small video camera probes quite cheaply nowadays if access to the tank is a problem.

To the OP - you may have changed your mind now anyway, but you need to use the low-carbon version of 300 series sheet material for a tank, either 304L or 316L, with filler wire of either the same material or 308. This will avoid sensitisation, that is the cause of weld corrosion in so many stainless steel tanks.

 

[Avocet]

The company I work for buys-in stainless automotive fuel tanks. They are a complete pig to weld and we and up pressure testing every one - with a fairly high rework rate. Personally, I wouldn't go there. Obviously, if you ave access to good sheet metal fabrication facilities, you can do a lot of folding to minimise the length of weld needed, but it's still difficult. Also, if you're just using flat panels, it will look pretty rough when finished - the distortion will be very noticeable. If it were me, I think I'd bite the bullet and go to someone like Tek Tanks for a plastic one. Less chance of condensation too.