dubious welding ?

[sardine]

I saw a guy working in a canal boat repair yard, he does all his MIG welds by laying overlapping tacks, in one second bursts, and its not thin sheet, or MIG pulsing, he was overplating a boat with 6 mm plate. Horizontal fillets, vertical buts, everything. The welds looked like TIG, with big ripples, and convex in profile, I m wondering about the strength of these welds, or whether its actually possible to weld like that seriously ?

 

[Steve Gray]

Hmmmm. Im no expert and new to the trade, but if the machine settings go high enough I spose suitable penetration could be achieved? ? Lack of reinforcement could be an issue thou?

Lets see what the pros say lol

 

[daleyd]

Seems fine to me

 

[marlinspike]

I was under the impression that the tacking technique was used when welding thin metal to prevent blowing through. Not sure why you would use it on thick plate. Was it definitely stop start? Some continuous welds can look like tack welding if you are using the technique where it looks like you are drawing an 'e'.

Is overplating the usual way in boats? With cars butt joints seem to be the recommended technique.

 

[wyn]

Sounds like the boat could have thousands of "cold starts" and leak like a sieve.

 

[BrokenBiker]

on 6mm plate you would need a huge mig in order to stitch weld with full penetration. I would prefer stick with a 3.2 or 4mm rod

 

[sardine]

Theres no pictures at the moment, as he's painted over it, he manually " pulses" the MIG in 1 second bursts, pushing forward, not pulling, the vertical butt on 6 mm had no edge prep at all.

You might be surprised to know there are absolutely no standards or regs on the welds on inland waterways boats.

I'd be worried about cold lap, but I only stick weld, I've only ever seen it demonstrated by my welding tutor years ago.

 

[BrokenBiker]

do you know what size machine he is using? if its something like a 300 amp 3 phase machine it will probably penetrate wll to be fair, if its just a sip migmate 105 then he is going to have problems when the weld fall off mid journey

 

[Robotstar5]

The guy in charge of welding at my last place used to build narrow boats in a previous job and always used a (big) mig welder.

 

[daleyd]

The guy in charge of welding at my last place used to build narrow boats in a previous job and always used a (big) mig welder.

I think the use of a mig is not the issue, rather the stop/starting of his technique. The little I know about welding seems to suggest it's not a great idea to stop/start all the time (Purley from an engineering point of view I wouldn't have thought it would do the welder a whole lot of good, all that stop/starting of the feed motor etc) but I guess if the boats are still afloat they must be acceptable

 

[Bill Edwards]

I won't say it cannot be OK - with enough power it probably could be. However, MIG tends to have poor penetration when you start - this is the reason you grind back the last bit of weld so you can overlap it when you have to do a stop/restart. For this reason it is correct to use it on a continuous run. The exception seems to be very thin sheet where this would blow through, but then you've a very high power relative to the thickness and you can often see the reverse to see what penetration you're getting.

Even if there's enough power available for this method to achieve adequate preparation I cannot understand why anybody would choose it over a continuous run, which is easy for a semi competent welder and quicker!

 

[dannyp]

with a big enough mig its not really a problem, i do it occasionaly mainly when i have to vertical up on a short section so rather than change all the settings just pulse it. there is a knack to it i think tho as leave it to long between pulses the puddel cools to much and end up with a line of craters,

i think it's bs2728 thats the old basic test, managed to get a test piece through that, vertical up T fillet in 8 or 10mm by pulseing it useing the settings that would normaly be used on a flat run. but that was with a resonably big machene and wire

 

[Bill Edwards]

I don't see the point (is laziness really an acceptable reason/excuse?) for not doing it properly!

 

[daleyd]

I don't see the point (is laziness really an acceptable reason/excuse?) for not doing it properly!

Surely doing it correctly (as one long run) would actually be easier as well? !!

 

[Bill Edwards]

Yes. No chance to mess up the amount of torch movement for each burst, nor the length of it.
Plus it should be considerably quicker!

 

[dannyp]

if it's just a few inches of weld, depending on what your doing, if your stood on the floor by the work and the welder you adjust the machene or turn the work, if you've had manover the wire feed into intrest positions to get the torch to reach and then had to climb over / in / on / through the work to get there and it's not a critical weld it's much easyer/ faster and less effort. as if you dont get the settings right you've only got to climb out again. then just to do it again once said small weld is done

 

[sardine]

In this case the welds are the entire length of various narrowboats. Over the cabin sheets of 12 ft wide yaughts ect.

The last customer gave up waiting for him to finish the job, which takes him about 10 times normal. Still you have to wonder at people that will let totally unqualified persons work on their boats, risking everything just for a cash in hand deal. I'm pretty sure no insurance would pay out if these welds failed and sinking ensued.

 

[PhillipM]

TO be honest, there should be no issues with penetration if the welder is set right. The HAZ would be worse than a continuous bead though, and the ripples obviously give somewhere for water to sit and corrosion to start.

 

[malcolm]

There is absolutely no reason to do strings of tacks on 6mm plate. It's a silly thing to to.

 

[dannyp]

ok doing whole sheets on narrow boats would be rather a lot differeant. on that kind of thing some serious thought would get put into trybg to get the weld in more preferable positions. if there was nothing to stop the boat being turned over it would be getting turned over.

tho some welders now do a really funky pulsed setting occasionaly do some welding for a customer that has quite a newish lorch machene and that pulses it's way allong, sounds diffrent but get the technique right and intime with the machene it can produce some really pritty looking welds that untrained eye would say are tiged