[Pyrobooze]

Greetings from Phoenix, Arizona.
This is my first post, but I am an avid observer. I am currently practicing stainless pipe, so I can achieve a cert in stainless soon. So... this past week I have been working on the 1g rotated, 2inch schedule 160 pipe with purged root (of course). I was very proud of my progression, because this is my first time purging a root. I am going to post pictures, and then I will ask my questions.


So I made the fixture for purging, since the recommended method of cardboard, and masking tape was a mess. I ran the entire thing at 85, and unlike welding carbon I noticed the root was pushing out more easily. I weaved my hot pass, and then ran stringers the rest of the way. I was very satisfied, but after showing it to my teacher he had a lot to say for it. Please give me your honest advice, and possible ways to correct my errors. Thank you in advance..

Pyrobooze

[Braehill]

Pyrobooze,
Welcome to the forum.

If you don't mind including a first name (nickname) it will make the responses a little more personal.

I'll make a few general suggestions and we'll let the guys with a lot of experience with stainless pipe give you more specific advise.

You don't need 20cfm for your purge for sure, 5-10 would be more than plenty. If you include more information you'll get better suggestions. Include things like what type of stainless, root gap, land, filler rod size and series, bevel angle and what's required for the test, as in a WPS. These questions will all come up so why not give the group the particulars up front and save answering 20 questions to get one real answer.

I normally use more than one fill pass on schedule 80 and up, using that root pass to just consume the land and give me a nice even weld reinforcement on the inside. With practice your root will look close to the same on the inside as it does on the face, the purge helps here. If you see that your root pass has too much pushed through you can run your first fill pass either a little hotter or a little slower to suck some of that filler back in. The filler metal is drawn to the heat. Try and aim for the center of the pipe as you progress around, this keeps your torch angle consistent.

Work on your terminations so you don't get the craters. Small circles as you reduce amperage with the pedal or if you're using a scratch start you can run back over the weld as you break out. Seat time will make you more consistent in your bead width so there's really no advise can take place of that.

Answer some of the questions I presented and we'll set about getting you on the right track.

Len

[Poland308]

Another note on the craters. If it's on a root and it needs to be exrayed for a test then a crater will show up and possibly get you flagged. I have trouble remembering about this. If your using scratch start on your root pass and on filler passes you can simply pull back on you arc length at the end of a weld this will let the puddle cool a bit and then you can walk the arc over to the side of the bevel to pull out. This takes some practice but will keep out craters. On a cover you can do almost the same thing but as you lengthen the arc watch the puddle close till it stops swirling and then pull out strait and fast.

[Rick_H]

Some good tips here above, I'd also recommend sanding the outside of the pipe around the bevel, keep from pulling anything into the weld. I usually scoor around front to back watching for the keyhole, laying the wire in. I'm not a huge weave guy unless I'm walking the cup, if you weave I found it hard for me to ensure my edges were always broken down. I typically will notnwalk the cup on anything under 4" unless it's a real awkward area and resting the cup helps me keep good arc length or angle, or overhead.

Clean in between passes very good, and let it cool till you can nearly touch it with your hand. On your stringers make sure you have enough overlap to tie in to each bead, most caps are only supposed to be 1/16" over...but that verys greatly depending on the WPS.

I assume that's a 1/8" gap? What size cup and tungsten? Your bead looks a little inconsistent are you resting on the pipe to keep it steady? Consistentcy is the name of the game with pipe, especially when you have to stack all those beads to fill a 160 pipe.

It's not horrible, I've cut out and seen much, much worse...with practice you'll do them in your sleep.

[Pyrobooze]

Hello guys Tim here,
Thanks for the replies. I have been busy putting in tremendous practice on this weld, and as you can see from the pictures I have made a huge improvement. So my school teaches us that there is a tolerance of 1/8th inch for reinforcement. With this in mind I finally submitted my weld coupon to be certified, and then I received a call from the inspector. He told me that for the particular codes I am certifying in there are 3 codes with 3 different tolerances, and 1/16th being the lowest. So he gave me back my coupon and said try again and to keep it at or under 1/16th. Now I am running into an issue. My root comes out beautiful, like butter. But every pass after is pushing my root out past 1/16th tolerance. In this picture I used a 3/32 electrode, knife edge bevel with a slightly larger than 1/16th gap. I ran the entire thing at 75 amps.any suggestions on how to keep my root from pushing out so much? Lower amps I come to find as I get closer to my cap is a lot harder to get a nice evenly fused bead. This is my first time attempting to get a cert, and after that inspector talked to me I feel like there is so much I don't know, and perhaps a stainless steel pipe cert is a little out of my league??

[Rick_H]

Are you letting it cool between passes? I generally go up about 5-10 amps per pass. Ensure proper fusion to the earlier passes.

Stainless is much more effected by heat and will drop out much easier. If your low on amps your taking longer which could be soaking the pipe in heat. What flow are you purging?

My rule and favorite saying for stainless is Get in and Get out as fast as you can.

Don't give up, you'll get it...Nice improvement BTW.

[Braehill]

Pyro,
You can also leave a little more land and you should get less push through. Let your puddle only take the filler that it needs. don't push it into the puddle. Rick's right, get your ass moving once you start.

You're improving nicely, keep after it, you're not far off now.

Len

[Poland308]

Your improvement is probably why the inspector wants you to try again he knows your very close to meeting the tighter specs.

[Pyrobooze]

Thank you guys for the advice, and encouragement. I understand that it would be better to increase heat, and travel speed. I also understand that I should not push filler metal into the weld. And finally , I should allow the metal to cool between passes. I will adjust to these recomendations, and report back sometime next week. Thanks again.

[Pyrobooze]

Hey Rick... you were mentioning earlier that I should lower my cfh on my purge to about half of what I was using. Will the higher flow rate affect the weld? I figured the answer was no, and more gas might even help to keep the metal cooler. Is this not the case?

[Braehill]

Pyro,
The suggestion to lower the flow was just to save gas. There are cases where too much flow can be a detriment, but probably not in your case. I don't think that you'll even recognize the cooling effect (97BTU @ 10CFH) in a coupon sized piece of pipe. I look at purging this way, I'm trying for zero Oxygen in the pipe and if I can get this with 3 CFH why send 30 through there and I work for one of the leading manufacturers of Argon.

When purging you need to consider the escape path for the Oxygen as well as the amount of Argon flowing. Common knowledge tells us that Argon is heavier than air and will settle to the bottom if contained. That's true and it would be great if the air was made up of just Oxygen, put the Argon hose in the bottom and vent the top, shut off the valve, viola. The problem is that the air that's surrounding and being introduced to the pipe is 78% Nitrogen (lighter than Argon) and 21.5% Oxygen (heavier than Argon). The Nitrogen is lighter than Argon so it escapes first and the Oxygen which is heavier than the Argon itself is what's left. This is where the flow comes into play, you have to have enough flow to displace the remaining Oxygen. Now when you set up your piece to weld you can flow at the higher rates for a short while to ensure you've displaced the remaining Oxygen by way of a total exchange of volume inside the pipe and then slow the flow to keep atmosphere at bay. You have to overcome atmospheric pressure on a flow meter to show flow, so as long as you have Argon flow going in, atmosphere is being purged. Anything more than that is just a waste of gas.

Len

[Otto Nobedder]

Len,

Did you really just say that atmosphere will stratify in a pipe being purged?

Maybe at cryogenic temperatures...

At room temperature, there is too much heat/kinetic energy mixing the molecules. I do vessel entries all the time, and I have never found a difference in O2 concentration, or any other gas I measure, between the top and bottom of a 6' "pipe".

Argon will not "settle to the bottom" while purging unless significantly colder than the atmosphere it's introduced to, because it is flowing and constantly mixing.

Best practice says to introduce your argon at the lowest practical point, but there's no practical science to support it.

Steve S

[Poland308]

A 43-year-old male furnace operator (victim) died after being overcome by argon gas in a pressure vessel measuring 3 feet 6 inches in diameter by 7 feet 6 inches deep. The victim was summoned by the vessel tender to enter the vessel and retrieve three tungsten carbide steel objects that had been dropped during the unloading process. The victim was lowered into the vessel by holding onto the hook of the overhead crane used to unload the vessel. The victim retrieved one object and handed it out to the tender, squatted down to reach under the vessel's internal heating element and retrieve the second object, and was overcome by residual argon gas at the bottom of the vessel.
Stratification in an open tank.

[Braehill]

Steve,
I did say that and with the Argon coming from a high pressure cylinder and going through a significant pressure drop, it has a significant temperature drop (i.e. frosted regulator with enough flow) compared to the static air already in the pipe. In a large vessel this temperature change will likely be nullified somewhat, but in a pipe not so much.If you put an Oxygen analyzer reading PPM per second (flow) on the vent of a pipe being purged with the Argon going in the bottom and vented out the top, the analyzer will read it's highest PPM of O2/s right before it drops to zero. Is there a 100% stratification, I highly doubt it, but it's enough in my mind to support what I'm saying.

I'm not sure if there's any scientific evidence of stratification, but it's the only thing that makes sense to me. I'm not sure if this can be verified on a large vessel, but it can be picked up on a piece of pipe and I've witnessed it on more than one occasion.