Ally welding..

[KemppiFrog]

Client wants a holding tank for his boat and at first thought stainless would the best. T'net thinks it is not a good idea as corrosion at the welds will be a problem. (Holding tank is where you store the toilet waste until you clear the 3 mile limit. Compulsory in most Med Ports)
Now he says to weld it out of 3mm ally and is not worried, as he thinks it is just to show he complies...

So question is: My Kemppi is up to it according to the specs. It has a euro torch conversion and I expect to get a Teflon liner and Argon gas.
So, any ideas on the tank. It is 2mtrs long and .6 wide. Weld from the outside? With brass heat-sinks on the inner corner? I told him I could make it in GRP, but no, it must be ally.
Any thoughts out there?
KF

 

[shenion]

Water-tight welds are difficult with MIG due to cold starts; especially on aluminum. TIG would be better.

I see no problem with stainless, the welds will not corrode if the correct filler wire is used (I would assume all 316.)

 

[rory1]

I've worked on various heavy marine waste systems, the majority having stainless tanks, I've not seen any corrode and some have been 20 years or older.

Copper pipe work corrodes badly with toilet waste, the urine rots away the pipe work- usually around the compression fitting olive or a soldered joint.

 

[F.J.]

I would also recommend using 'U' rollers if you do go down the ally route. I used to use standard 'V' rollers but once I changed them over I really noticed the difference.

Just a thought with the cold starts, would a little pre heating not help out?

 

[Jim Davey]

If you can get them you want semi-circular rolls, not U or V profile. Poor starts can be overcome by dressing the starts down with a grinder and running the next weld into the start and coming back on yourself about half an inch before releasing the trigger. But as said by others, stainless seems to be the more suitable material for the job.

 

[KemppiFrog]

Thanks everybody. I will try to talk him round to SS. Easier for me as I have 316lwire and gas already + done quite a bit.

 

[Cobbler]

Public toilets use stainless for the pans & urinals, never seems to be a problem with those.

 

[julieanncharters]

If you can get them you want semi-circular rolls, not U or V profile. Poor starts can be overcome by dressing the starts down with a grinder and running the next weld into the start and coming back on yourself about half an inch before releasing the trigger. But as said by others, stainless seems to be the more suitable material for the job.

like Jim Davey says Ali weld finishes/starts need back chipping with tct blade in 4" grinder then weld back to them to get air tight cap, back step technique.
leaks tend to occur at the stops and starts on Ali mig.
can't see Ali even 5083" marine "grade being ideal for waste long term.
doin tanks in Ali ,tig would be the tool of choice for me.
push for the stainless 316 better long term choice by far.

 

[Ed.]

I had a similar problem about 12 months ago as I needed one for my boat, after considering all the possibilities I decided to get one made out of 8?mm PVC, I do have a plastic welding gun but ended up going to a plastic fabricator as he could make it cheaper than I could due to his purchasing power on the PVC sheets. PVC will never corrode due to septic waste and PVC fittings are everywhere.

Cheers

Ed.

 

[KemppiFrog]

I had a similar problem about 12 months ago as I needed one for my boat, after considering all the possibilities I decided to get one made out of 8?mm PVC, I do have a plastic welding gun but ended up going to a plastic fabricator as he could make it cheaper than I could due to his purchasing power on the PVC sheets. PVC will never corrode due to septic waste and PVC fittings are everywhere.

Cheers

Ed.

He has something against plastic. My suggestion for a GRP tank was turned down.

 

[Ed.]

No problem, I can see where he is coming from though, as a lot of resins aren't suitable for septics/holding tanks, the acidity eventually chews through them and hard to seal the fibres in the internal baffles and joints, plus flexing etc. etc.

I rang a few septic cleaning places for advice and they basically said that even though their tanks on the trucks were out of 10mm Ally they too would eventually corrode and they replace them after a while. Hence the decision for PVC, last thing I would want is for a septic/holding tank to crack or leak whilst cruising on a boat.

Cheers

Ed.

 

[Charlie]

Hi, my name is Charles & I would like some help/advice on stick (MMA) welding Aliminium. Years ago, I can remember welding Alli using this method but cannot remember the machine used and/or it's settings. i have a 150A D.C. welder & a Cemont 160 inverter for TIG & MMA welding. I have tried both machines but with no success. I'd like to weld outboard motor props to supplement my income. Can anyone out there advise?

 

[Jim Davey]

Due to the corroded and salt impregnated nature of ally boat props you really are best Tig welding them, the cleaning action of the Tig weld pool will greatly assist you.

 

[dannyp]

MMA ali welding is not a prosses of choice,

it's a party trick that few can do and genarly only do when there is no other option.