Stainless TIG test dipped Options

[NeeGood]

Alright lads.
Recently done a 5G Stainless test 8" pipe about 6mm thick. got it set up plugged both end with sponge, purge line in (normal carry on) and set argon away at 4 lpm. Only problem was didn't check root till i'd finished just exspecting it to be spot on. Sponge out have a look and it's all went tits up! Cause of the volume of the size of the pipe maybe I should of had my purge running higher, Maybe 8 lpm or so? Thing was argon seemed to be coming out fine. What yous think, More argon??
Thanks Lads

[douglas]

I always make a window out of a clear welding screen lense and use masking tape so as to see my pitiful progress! On the purge rate, I ram the flow rate right up as high as it'll go for a minute and then reduce it down to around what you're saying. The key with purging is, as you say, volume. In theory you could have no flow rate so long as the void is gas full. Every butt is a new butt. Hope you get a re-test fellah and watch it this time!
Good luck
doug.

[NeeGood]

Cheers doug.

[Butt rustler]

Have you done much stainless mate?? Seriously 4 LPM?? What were you trying to fill?? A balloon?? And these sponge things you speak of, they're generally called dams!! Did you have your 'sponges' covered with masking tape or were they rubber sealed?? If neither they will just act as a filter.

[OverWelding]

I have to concur with Butt rustler, 4lpm????
Seriously, anything over 4" you've got to pump that argon in.
Me personally....at least 15lpm, and not just the 'pepper pot' on the other end.
If its taped, at least the same size outlet as inlet.
If its a 'sponge thingy' dam then put a hose for a drain.
When you put your ear to the outlet, that gas noise you hear is probably the air being pushed out.
Give it a minute or so to purge and keep the pressure up.
Also, use a diffuser, even if this is just a piece of sponge taped over the end of the purge hose.
I welded for years without these, but now I'm converted and swear by them...especially on the 'exotics'

[whittm]

Really nice simple tip with purging i learnt. You dont need a special sensor or have to guess how long it takes to expell all the air. Its as easy as this: Wet your finger and hold it near the end of the drain, as soon as the air is fully expelled you will notice a sudden drop in temperature. I'm not sure why, but I think its due to the relative density of argon compared to air, argon has a higher density and therefore more molecules to convect the heat from your finger? Whatever, it works try it!

[nanjing]

Do you not have a Welding Engineer to give you direction on how to purge? Purging requirements are beyond a welders capability to work out especially for the higher alloyed stainless and reactive materials.

[skaginn]

nanjing
Welding Engineer you are having a laugh.
In theory an engineer could work out how much gas has to go in to displace x volume of air , in fact some procedures do state a flow rate for the purge this is normally taken when the procedure was welded but is only a basic guide.
In the real world the combination of variables when purging you need to know what you are doing even when using a sniffer. There is no substitute for experience when purging just read some of the posts on the subject.

[nanjing]

Don't need to read previous posts that is why I get paid big bucks. In the last year I trained 25 welders to weld SMO in China for extreme service conditions +40C Cape Preston Australia. Owner is extremely happy so do not give me any beept about "real world".
You do not have a clue about experience I have been doing this for over 35 years.

[gedtodd]

Amazing response nanjing.....do us all a favour and give your "big bucks" to a local charity, along the the way, you may become a little humbler.

[apprentice]

Big bucks eh!! If you are that clever, then why do you have to go all the way to China to earn them??? I am pretty sure the Chinese are more than capable of devising welding procedures and training welders all on their own.

The original poster left a perfectly sensible message asking for advice, so there is no need to try to be clever. Just remember that "pride comes before a fall"

It is all very well some welding engineer coming up with a figure for purge rate, but as a previous member stated, this would be merely a guide. There are so many variables involved that this is all it ever could be.

As for stating that it is "beyond a welders capability" to work out these things for themselves, i shall do no more than give you a quote from the great victorian inventor and engineer James Nasmyth. "Any fool can tighten a nut with a pencil" Think about it...

[Butt rustler]

Don't need to read previous posts that is why I get paid big bucks. In the last year I trained 25 welders to weld SMO in China for extreme service conditions +40C Cape Preston Australia. Owner is extremely happy so do not give me any beept about "real world".
You do not have a clue about experience I have been doing this for over 35 years.

Nanjing, I have read many of your posts on here and you're very knowlegable. Why are you getting involved in this??

[gregyboy]

Nanjing is a welding engineer, a bit like a politician, of the welding game, they have fixed ideas on how things should be done, it would be interesting to see if you put a torch in there hand, how they'd get on!

[Technic Al]

Im not defending nanjing. Nanjing is Nanjing he has an ability to wind people up and only he knows why.

Leaving that behind. A Welding Engineer is a Welding Engineer and a Welder is a Welder. The two should compliment each other not antagonise. Im primarily a Metallurgist but Im also a qualified Welding Engineer. I would always consult my Welders before I put pen to paper. I wouldnt expect Nanjing to be able to hold a torch....why should he

Ive also been offered "big bucks" many times and to be honest it turned out I was getting paid more in Rotherham

So "big bucks" are relative

Premiership footballers are big bucks in my opinion, unfortunately Welding Engineers come a very distant runner up

[douglas]

Hey neegood

*Explicits deleted*

hope all goes well.

Differing levels of inteligence noted.

doug.

[NeeGood]

Aye Doug. All taking in.

Thanks for in put lads.

[Ballbearing]

Hi guys,
First of all, Nanjing has admitted many a time that he couldn't burn two bits of toast but as Technic Al stated he doesn't need to know how to weld, he needs to know how to provide relevant information to the welders so they can produce sound welds.
Secondly, no one has commented on the fact that Neegood either didn't have a WPS or maybe did not understand the WPS.
Any half decent WPS has Shielding Gas / Backing Gas - Composition of both and flow rates of both. If the WPS had 8 - 10 lpm then of course he would not have been purging at 4lpm.
TWI have put out a good paper "Gas purging for stainless steel pipe welding" where they give graphs showing how long it takes to successfully purge a 150 nb pipe at 10 lpm, 20 lpm and 30 lpm. After the initial heavy purge they recommend 4-6 lpm during welding. So Neegood was not too far off in purging pressure (during welding) but he obviously did not "blast" the oxygen out with a heavy initial purge.
Cheers,
BB

This post has been edited by Ballbearing: Jul 13 2010, 06:44 AM

[NeeGood]

There was no WPS to work to BB or I would of liked to think this topic wouldn't of been posted mate. I did give the test pice a blast out first but must not have been long enough. Thought 4 lpm was about right BB so thanks for the post.

NG

[Ballbearing]

Neegood,
This is an approximate time of how long you should have purged based on 25 CFH (Cubic foot per Hour) or 11.8 lpm.
251 seconds at 25 CFH (11.8 lpm) per each 300 mm of 8" pipe.
Say 300 mm for 2 x 150 mm long test coupons.
At 4 lpm that will take approx 12 minutes to purge.

These times are based on no initial "blast" of argon so as you can see when you are just dribbling the argon in it takes a while.
Cheers,
BB

[loswf]

This is an 8 " test piece not a tie in butt on a long line it would take less than a minute to fill up. pierc a hole in the dam and away you go. you shouldnt need a welding engineer to show you this .