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Up Topic Welding Industry / General Welding Discussion / 6 Mo Vessel to be fabricated
- - By welder5354 (**) Date 05-15-2010 04:59
One of our customers want us the build a vessel using 6 mo material.
We have to roll the plate and weld the heads on.
So we will have one seem weld and 2 circumference welds.
The manhole will be 12 inches.
The tank will be GTAW and SMAW.  The vessel will be 8 ft high and 6 ft in diameter.
What will be the best way to purge the tank for the GTAW process on the first pass.
Has anybody got some good ideas for the cheapest way to save on purging gas or some other
way to complete the tank without having to fill the vessel with argon.
Tks, would like some ideas.
Parent - - By weldwade (***) Date 05-15-2010 16:29
I've built clamp on or magnetic back purge devices for several out of the ordinary jobs in the past. Get some thin sheet and cut it to the ID radius and fab one up, have your helper move it for you as you go.

What is 6 mo material?
Parent - By Tyler1970 (***) Date 05-15-2010 20:38
monel maybe?
Parent - By welder5354 (**) Date 05-15-2010 23:22
6 mo as we call it.  Has a high content of nickel.  It is similiar to stainless steel.
At our shop we have heavy duty rollers, so i guess we can fabricate a backing purge (maybe from aluminum plate)
and then bend the plate to the curverture of the vessel.  Then we can tape the plate to the inside of the vessel because magnets will be no
good on this material.
I believe that should work very good.  If anybody else has a better idea, i would appreciate the info.
Tks for all
dh
Parent - By combofieldhand (*) Date 05-16-2010 00:10
actually, I welded some 24 inch chrome recently and came across a similar issue, I took a soup can and drilled a hole into the bottom of it so my purge line could fit thru, them i cut two 7/32 deep grooves into it, right across from each other on the lid side ( for the root to have a open way). as we beaded it, someone held the can over the root so that it could be purged as it was welded without having to close off the whole piece of pipe. but thats just my 2 cents.
Parent - - By js55 (*****) Date 05-17-2010 12:51
I wouldn't purge it at all. Something of that size I'd double bevel it with a closed root gap and then backgouge/grind to clean metal and weld the other side.  This will not only save on purge gas, and welding time, it will reduce the volume of weld metal required which is important since you should be welding it with a hastalloy filler, generally 122/622.

By the way, which 6 Mo? There is a whole family of those alloys. And be careful, you will find some of them are P-43 (like 254SMO)and some are P45 (like AL6XN).
Parent - - By Metarinka (****) Date 05-17-2010 21:20
I concur with Js55  with a joint that big you might want to look at minimizing joint volume and a double bevel is less so than a single bevel. As mentioned then you would only have to grind to sound metal and weld the other side. After that it sounds like your using smaw for the fill.

If for whatever reason you have to stick to a once sided joint for welding.  We make a purge cup out of a box (fabricated in the shape of our work) with a sintered metal front to diffuse the gas, usually only need a 4-8 long cup.  Get another welder or shop hand to follow the weld with the cup. you can make them all fancy with wheels or pads so they ride right on top of the root opening a set distance. I would try to get away without having to purge though.
Parent - By welder5354 (**) Date 05-18-2010 00:13 Edited 05-19-2010 01:05
I think Js55 your point of view is good.  This material is 254 and 1/4 inch thick.
So i think we'll SMAW weld the inside first and then grind from the outside and then backweld.
This should be the easier and most economical way of welding this vessel.
We have large rollers to roll the vessel and so we can do all the welds in the flat position.
tks
- By PipeIt (**) Date 05-18-2010 11:13
You most likely know this already, but for good measure, I'll caution you if your inside the vessel and your using the GTAW process make sure the shield gas Argon has a place to exit.

Its heavier then air and will fill the vessel like water would, I heard a bad story on welding on Bridgman Nuke back in the 80's where this wasn't taken into consideration, I was not directly involved but one of my old tool buddies was. 6 died from asphyxiation.
- - By welder5354 (**) Date 10-30-2010 04:00
Well the vessel is all complete now and go to the customer.
We welded the inside first and back grinded on the outside and then completed the welding.
The nozzels were welded with GTAW.  All welds were ex-rayed, lpi and visual.
Actually is was a very good job, now that it is all complete.
Parent - - By G.S.Crisi (****) Date 11-03-2010 22:05
You Americans must be pretty thin to pass through a manhole 12 inches in diameter.
Giovanni S. Crisi
Sao Paulo - Brazil
Parent - By TimGary (****) Date 11-04-2010 12:14
We just compress our bodies like cats.
Any hole we can get our big heads through is big enough. :)
I'm 6' 2" tall, with 2' wide shoulders and average 200 lbs.
Thank the good Lord I don't have to do it any more, but I've crawled through a lot of manholes, snaking my way through double bottoms of ships, and between tank baffles, all while carrying welding, cutting, gouging and grinding equipment.
It's all OK, except for the gouging. When your stuck inside a small space, gouging is no fun at all.
What really stinks is when you get all the way in there, and get set up, and after you realize you forgot something crucial, and have made a second trip to get it, and then as you're finally about to get started, your light bulb breaks.
If anybody gets stuck in a man hole, They'll most likely never do it again because their "Buddies" will generally take unfair advantage...
Up Topic Welding Industry / General Welding Discussion / 6 Mo Vessel to be fabricated

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