Rules to when to multi pass/how many passes?

[Dbzrocks]

Hi, I’m new to stick welding, iv done a very small amount but I’d like to get better at it.

My understanding on multi pass welds isn’t great could anyone explain to me when you know when to use multiple passes and how do you know how many passes to do?

does it go by overall bead size vs the thickness of steel your welding? By this I mean let’s say I weld 10mm thick steel (two pieces of 10mm) fillet weld. Would the weld need to be a certain size or as thick as the material welded?

Can’t seem to find anywhere that really explains this so it would help me out greatly and maybe some others that are learning.

Many thanks

 

[Taylormade100]

I am no expert so someone may prove me wrong but I was taught a fillet weld on 10mm pieces of steel, the weld should be 10mm wide ( the same as the parent metal). Depending on the size of the rods used, you lay a run in the corner of the 2 metals, then another along the bottom and then another along the top. You keep doing this untill you reach the desired thickness of weld. You can also buy gauges to measure the weld. I hope that makes sense.

 

[BrokenBiker]

Multi pass welds, in my experience, are to build a weld size up so the throat depth is equal to or greater than the thickness of the parent material being welded. This can be done as a substitute for not having the correct size rod, for instance only having a 2mm rod when ideally you want a 3.2, or for when it's just not possible to put a huge weld down in 1 go, like trying to stick weld a fillet joint on 2 bits of 20mm steel, you would want more than just 1 pass there.


Pro welders will be along shortly with more technical info and very probably reasons for why you wouldn't want a multi pass in certain circumstances

 

[8ob]

Hi, I’m new to stick welding, iv done a very small amount but I’d like to get better at it.

My understanding on multi pass welds isn’t great could anyone explain to me when you know when to use multiple passes and how do you know how many passes to do?
does it go by overall bead size vs the thickness of steel your welding? By this I mean let’s say I weld 10mm thick steel (two pieces of 10mm) fillet weld. Would the weld

It depends on the rods and amps used, you could easily one pass on 10mm with the amps cranked up and a 4mm rod, or you could root run and cap with a smaller rod.

Bob

 

[chrismac]

Good advice already given, what work you doing..... back yard or procedure?

Some procedures only allow as an example weaving 2 x filler metal thickness, that would be the governing factor.

 

[Dbzrocks]

Good advice already given, what work you doing..... back yard or procedure?

Some procedures only allow as an example weaving 2 x filler metal thickness, that would be the governing factor.

just doing as a hobby but was curious as i want to know more about welding and when it’s needed to multi pass etc as Im going to make some thing with thicker steel etc that I want to be strong enough

 

[Matchless]

I am a weaver, self taught at about 10 years old, made go-karts and toboggans for the kids at school!

 

[Pigeon_Droppings2]

I know very little about stick welding...but I do know mathematics.

My "guess" would be that the total joint weld thickness needs to be set to allow the loads to go thro at the very least a similar thickness of weld as the parent material.

No idea if this is correct but just based on logic of how the loads would be transferred.

 

[BrokenBiker]

just doing as a hobby but was curious as i want to know more about welding and when it’s needed to multi pass etc as Im going to make some thing with thicker steel etc that I want to be strong enough

What sort of thickness are you thinking of welding?

And what sort of power does your welder put out?

 

[tom2207]

the old wisdow was never weave more than 4x diameter of rod ,,, and throat thickness to the same or greater than parent metal ,,, but thats just for farmers really ,,, after that its either follow the weld procedure , or get out the text books

 

[Bornfree]

He Here's a recent repair its a 20mm thick tractor lift arm this needed multi pass. I did the root run with tig followed by three runs with 4mm 7018s each side.

 

[Munkul]

There aren't many limitations on the number of passes you can do in a joint, but there are a number of caveats.
1. Usually on thick steel with lots of passes, like 25mm+, you should have a pre heat. Then, Interpass temperature, so you need to keep a minimum temp between runs.
2. Interpass temperature on stainless and duplex and high strength steels is limited, if you go too hot it ruins the corrosion resistance or strength properties.
2. Joint restraint and hydrogen cracking - generally you need low hydrogen process to do many passes. Otherwise, the internal stress of the joint builds up pass by pass, and you'll get hydrogen cold cracking if not using low hys or MAG.
There are other caveats as well, but that's off the top of my head.

Ideally you complete the joint in as few a runs as possible, as time is money, but as pointed out, you can only put so much metal down in one pass at a time.

 

[Hitch]

There are charts that reccomend weld sizes, one for structural applications that gets used as a rule of thumb is AWS 7.7, it reccomends weld sizes based upon material thickness.

With regard to fillet weld-
Below 6mm thk would be 3mm leg, 6-12mm would be 5mm leg... 12-20, 6mm leg... might be a handy rule of thumb for you.

Depends on your equipment and consumables, a z6mm fillet might be difficult to achieve... so you could do multi pass, root, then 2 more runs to achieve the reccomend 6mm.

There's also a boat load of other things like how the parts are loaded, static, cyclic etc etc to take into account, CSA of weld profiles, leg and throat thickness relationships....heat inputs...a pretty in depth subject.

What sort of thing are you attempting to weld?