Sporatic porosity in weld

[OperaHouse]

I have a friend that manages a BIG weld shop, they can do everything but a N stamp. At two stations next to each
other they are getting sporatic weld porosity. This will last from a few to maybe 15 seconds. The welder has 25
years experience and doesn't have any problem when he works in the other part of the building. One welder is a Miller
inverter Pipework 400 operating at 300A 28V using flux core wire with an argon 75/25 blend. The other welder is
a transformer type and it can experience the same problem. They run off a 480V line that seems well balanced. I
would think an inverter type would be less sensitive to a sag in one leg. There is no visible or audible change
when the porosity happens. The same wire and gas is used in the other location without problem. They blend their
own gas with a THERMCO mixer (see note at end if you own one of these) and I built an alarm system that goes off
if the mixers ever get out of range. I've checked the electrical and don't think that is a problem. I would suspect
a gas issue with maybe some condensate entering now and then. The flow gauges are clear and show no signs of
streaking. I wanted to pull apart the gas regulator to look for signs of contamination but they were in use.

Short of this space being posesed by a welder who died on the job, We are at a loss as to the cause of this problem.

ATTN: THERMCO OWNERS. These mixers were picked up at a good price because the monitors would no longer cal. Factory
said buy a new box for over $2K each. I performed a modification, not as hack, that doubles the life of the monitoring
cell. These work by comparing thermal conductivity of the gas with a reference. Over time the fine heating wire is
eroded and changes resistance. These resistance changes are very small and the cells are a mirror image of each other.
Flipping the wires and plumbing to the opposite side brings the system back into cal. If your front panel control is
at the end of its adjustment, perform this procedure. I have the procedure written up and you can have it for free.
If you have basic solder skills, you can save a couple thousand.

 

[Duwe6]

Sounds like a shielding gas issue. Probably not from the bottle, otherwise ALL the weld would be bad, not just portions. Drafts will blow away the gas. Or somebody stepping on the supply hose, prior to it joining with the welders 'whip'.

Other possibility is flux voids [or partial voids] in the flux-core filler wire. Try switching out the roll, to another brand. One of the more common 'False Economy' items in weld shops is cheap filler materials. When they cause even one repair, your savings evaporate.

 

[weldstan]

Have you checked wire feed speed, voltage sense lead at the wire feeder, and contact tip wear?

 

[EdStainless]

I would start by replacing any gas lines that are rubber or plastic. They become porous over time and leak and trap moisture.
Then I would leak test the lines and joints. It is best to pressurize with He and then sniff with a mass spec. Start at very low pressures because you will find many leaks. Where ever gas can leak out air is leaking in.

I have seen this with uneven gas flow, the sag and surge in flow can lead to instability and porosity.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[gtaw]

Check with the welders to see if the porosity occurs in the morning or at the beginning of the shifts after the machines have set idle for a while. Many GMAW/FCAW machines do not incorporate a prepurge to purge the air from the gas lines between the wire feeder and the gun. Thus, air is the first gas to exit the gas nozzle until the air is completely purged from the gas line. The results is weld porosity due to insufficient shielding gas for the first inch or two of weld.

One way to mitigate the problem is to teach the welders to tap the trigger a couple of times to start the flow of shielding gas, thus purging the hose of any air.



Best regards - Al