Can Flux Core Wire Go Bad Title Image

Does this sound like you?

You’re about to do some welding. But you’ve realized the last time you used your welder you left your flux core wire in it.

How long ago was that? 

You’re struggling to remember.

And now you want to know does flux core wire go bad. Does it rust?

How long is your flux core wire good for before you should get yourself fresh wire?

Can Flux Core Wire Go Bad?


It can and does.

And you’ll get yourself a crappy weld.

The enemies of your flux core wire are moisture from the air. And if you live in a humid climate then you’ll need to watch out.

Water soaking all or part of your flux core wire is an issue.

Have You Wondered How Does Flux Core Wire Go Bad?

The worst thing you can do to your flux core wire is store it badly.

What is storing it badly?

Leaving it in your welder for 6 months to a year isn’t great.

Or just tucking it back in its box without anything to protect it is also not a good idea.

Because you risk the disappointment of a failed weld. And a weld that has tons of porosity.

Want to know what causes your flux core wire to go bad?

The Way Flux Core Wire Is Made Helps It Go Icky

Part of the reason why flux core wire gets spoiled is the way it’s made.

You’ve the flux in the center and your metal around the outside like a tube.

Flux Core Wire
Flux Core Wire

That’s why its called flux cored.

This means there is a seam all along your flux core wire where the metal wraps and joins.

And that seam isn’t sealed in all makes of flux core wire you buy.

The Way Flux Core Welding Works Helps The Wire Go Stale

Because the fact is, that flux core welding is a low hydrogen welding method.

So what?

You’ll find that tiny particles of water seep into your flux over time from the air.

Then you get moisture in your flux.

And then when you start welding with your flux core wire, the moisture / water breaks down. It breaks down to its component parts of two parts Hydrogen to one part Oxygen in the heat of your welding arc.

And this means you then have extra Hydrogen in your hot metal weld pool.

Extra Hydrogen ups the Hydrogen in your weld. And then you have high Hydrogen in a low Hydrogen welding method.

This then gives you a poor weld. And that means a weld that cracks and breaks.

Does Flux Core Wire Rust?

Yes! it certainly can.

Mild steel flux core wire is open to rust.

It’ll rusts from moisture in the air. And water soaking any part of your flux core wire will rust your wire over time.

Even wire that’s inside my welder?

Yes. Your flux core welder isn’t a sealed unit. And is likely air cooled and has air vents.

The cold damp of winter, or the humidity of summer can rust your wire.

And make your wire tricky for your welder to melt properly. Weld erratically and spit spatter all over.

Question Mark Icon

How Can I Tell If My Flux Core Wire Is Rusty?

Have you forgotten your flux core wire in your welder since you last welded 6 months ago?

Or did you remove it from welder. But put it back in its cardboard box just as it was?

Take a look at it. 

Take the spool of wire out of your welder and pull it out of your hose to your MIG gun.

Keep hold of the wire on the spool. You don’t want it pinging off.

Look Closer.

Can you see clear signs of rust?

If you see some rusting, then unravel 20 feet of the wire. Can you see clean wire still on the spool?

If you can. Then you may get lucky and the rest of the wire on the spool is fine.

Wind out and cut off all your rusty flux core wire till there’s clean wire left.

Because dodgy wire is not good on a critical weld?

Critical weld?

Does your weld have to hold weight? Is it a weld that could cause you or someone else injury if it failed?

Then a spool of fresh wire is what you need and save your worry.

Does Flux Core Wire Expire?

Yes it does.

Or at the very least it has a best before date.

Here’s what a selection of the leading brands say about how long their flux core wire last.

And would you believe that the shelf life of your flux core wire varies?

Blue Demon Flux Core Wire Expiring Conditions

Boxes should be kept sealed until you’re ready to use. And as long as the boxes are stored in less than 60% humidity. And between the temperatures of 50 to 110 degrees Fahrenheit. Your wire should last you at least 1 year.

Here’s a link to their document.

Lincoln Electric Flux Core Wire Will Last You

Lincoln Electric says their wire will last you 3 years from date of manufacture. And this is for unopened packets. So you’d be well to check when the packet you bought was made.

And they say these 3 years applies to packets that you store well.

And this means below 70% humidity.

Once opened the flux core wire is open to moisture in the air.

And Lincoln says use your opened wire within a week.

But you can protect your opened wire by taking it out of your welder. And sealing in air tight plastic bags.

Here’s a link to their document. Go to page 58.

Hobart Flux Core Wire Will Hold Out Till?

Hobart Brothers provide a 1 year warranty from shipping for unopened packets.  So you have a year with your flux core wire on the shelf.

As long as you store your wire between 40 and 120 degrees Fahrenheit. And the greatest humidity is at 80%.

But they’re clear in saying moisture must not come into contact with the packets of flux core wire.

There was no comment on my question to them about how long an opened packet of flux core wire would last.

You can take a look at the document on the Hobart Brother site they referred me to.

ESAB’s Flux Core Wire Will Expire

The length of time ESAB’s flux core wire will last you in a closed fresh box depends on the packaging they send it in.

As long as you store them well. And this means you keeping your flux core wire between 50 and 90 degrees Fahrenheit. And where humidity is less than 50%.

Their vacuum bags they say will be fine for 5 years from manufacture date. Other packets 1 year. And this is true for their gas shielded and self shielded flux core wires.

You can check out ESAB’s document on this here.


I have an open question out to INE on how long you can expect their wires to last before they expire. And will update this post as soon as they respond.

Even Newer Flux Core Wire Can Go Bad.

Because of your own local welding conditions. Lots of moisture in the air could get to it.

And you can’t always tell by looking.

When you’re getting a nasty weld, and you’re sure your welder settings are fine. It’s worth trying fresh wire.

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