Welding Tips and Tricks

Hi all,
When purge welding a 1000 liter tank, 2mm stainless,
What would be the right L/ min flow rate to fill the tank be? And while welding a different flow rate?
I don't have a purge meter to determine when to start welding... Is there another safe way to determine when to start?

Cheers Ben

What kind of shape is this tank?

Usually pipes can be flushed with high speed purging, but flow needs to be laminar. Tanks are different story. I would recommend 10-15 l/min during filling and 5-10 l/min during welding. There is thin line between good purging and wasting gas. Are you using argon or hydrogen mix? It makes a big difference.

There is formulas to be sure that enough time is consumed until you can start welding. I don't have the formula right now in my hands, but will check it for you later.

Ben,
Have these tanks had anything in them prior to this? If these tanks have been used in flammable service I would recommend getting an explosive meter. If these are new tanks just being built, then just do the math to get close.

You're going to need quite a bit of gas to purge a 1000 liter tank so if they have to be purged with Argon, I would suggest getting a dewer of liquid Argon. Personally I would check into being able to purge it with Nitrogen, much cheaper and also available in liquid dewers.

What are the tanks made of 304,316,321,duplex?

Len

This is how to calculate purging time, if you don't have purge meter.


Purge time (minutes) = [Volume (litres) x Change over] / Gas flow (l/min)

* Needed times to change the volume "change over" is 5-10 times.



Example:
Volume = 1000 l
Purge gas flow = 10 l/min
Change over times = 5


(1000 l x 5) / 10 = 500 minutes or 8,3 hour


Remember that argon is heavier than air and nitrogen and its mixes is lighter than air. So it really matters how you purge the tank.

@Markus @ottonobedder @braehill have you ever had to weld the top of a large vessel and fill it up 80-90% with water then purge the small area left?

Rick_H wrote:@Markus @ottonobedder @braehill have you ever had to weld the top of a large vessel and fill it up 80-90% with water then purge the small area left?

No but I have had very bad experience about water/moisture in long pipe lines. Purging pipe with moisture in it will create somewhat awful root.

I have to weld some tool steel parts and I put them in a small pan of water with just the part that needs to be welded above the water to keep them from getting hard all the way through. I have to be careful not to create any steam because it makes a mess out of the weld.

The reason I was asking is I have heard this done, but I personally have never tried it. Only thing I welded with water in it was a gas tank....

I've never welded with water and a purge.

I have welded a fuel tank full of diesel fuel and welded a water line with water running out of a crack. The water line turned out fine, but the fuel tank built up pressure and the cap hit the ceiling right before hitting me on top of the head. I finished it without the cap on. The water line got replaced shortly after that and I didn't get a chance to look inside the pipe before it got tossed so I have no idea what the inside looked like. Both were carbon and didn't require a purge.

Len

I've done lots of boiler lines and condensate lines that had water pouring out of them cause they couldn't afford to shut down till the next holiday. Often it gets left till two or three places get patched. As long as you can limit the pressure build up its workable.

Field work, I have purged(fuel Tanks) with exhaust with hose from a running internal combustion engine i.e. car/truck engine