[RedIron881]

Happy New Year to all my fellow Weldors!

Ever come across those really hard to reach spots that you just can't get into? Here's a handy trick to keep in the back of your mind and in your Tig Kit. Having a few bent tungstens with different angles and lengths can be really great. I can't thank my old lead weldor enough from years ago showing it to me.

How do you bend it? Simple. Holding the sharpened tungsten with two pliers into a propane torch flame till its red hot you add some pressure and it will bend.

Things to keep in mind though... You have to keep the angle within the gas flow of the cup so shouldn't go more then 45 deg or so. You want to bend it far enough back to be able to reach around what you want and also so you can sharpen it a bunch of times after being bent. After awhile you'll just sharpen the bend right out of the the tungsten.

I keep around 5-6 bent tungstens in my kit with different lengths and angles sharpened ready to go. Mainly for the job in the photos we do a lot of at my shop. Hope this might help a few of you out when those crazy spots come across your tables.

Have a great New Year!

[ajlskater1]

Wow never seen that before. I have been lucky enough to always have a flex head but that is a neat trick. Does the type of tungsten matter.

[Otto Nobedder]

Yep, I've had to do that one before. One common modification I do at work involves moving a vent line (1") to the top of the main vent manifold (4"). This puts the back of the weld, in some cases, within 3/4" of the main vessel. A 90* microtorch would do it, but this would be it's only use, ever, in the shop, so it's just far more practical to use a bent tungsten.

This weld sometimes requires a 3/4" dental-style mirror to accomplish.

Steve S

[ajlskater1]

Never welded with a mirror that would be fun to learn. I do big turn table stuff at work so its all really open but at my home shop that will be a good trick. Would have in handy on some welds I did on my last project.

[Otto Nobedder]

Mirror welding messes with me in two places.

The first is when my weld is at the edge of my sight, and I have to stop and set up the mirror.

At that point, I have focus on the mirror, and things are "backward".

The second is worse, when the weld comes out of the mirror and I can see it straight-on again. This is the biggest moment of confusion, and I usually have to stop and walk away for a few minutes.

[ajlskater1]

I bet seeing things backwards would be weird. I weld backwards on the turn table sometimes and that took awhile. So with a mirror would probly take awhile I should practice at home.

[TamJeff]

Cool. I have done that. I knew Otto would have in his work once I saw the manifolds in the other posts. I have also done that using the gas flow from a purge tube flowing down into the blind area when I knew I only had one shot at it. I have to do trapped repairs from time to time. Bent tungsten and bent filler.

Good stuff to know.

[Otto Nobedder]

Might be doing it here, for the pipe on the left. Only an inch of clearance at the bottom.

GEDC0505.JPG (183.77 KiB) Viewed 5644 times

Going to be some mirror welding, too. I'm replacing this section of the expansion loop.

GEDC0509.JPG (210.86 KiB) Viewed 5644 times

The missing ell is where my leak was; It was deeply dented by the work another shop had done. (They had no reason to suspect it had happened; It took me almost a week to figure out how it happened.)

Steve S

[TamJeff]

Do you get to build any of that on the table?

[Otto Nobedder]

Yes, fortunately.

There'll only be the two position welds you see, and the one on the left will have a backing ring (a last minute decision... the pipe was distorted, and the effort of rounding it out flared the end slightly). I can build the leg I'm replacing on the bench.

[Alexa]

http://www.weldcraft.com/products/wp-se ... specialty/

[Otto Nobedder]

It occurred to me to get a couple shots of the damaged ell, where the leak occurred. You'll note the extreme deformation.

GEDC0510.JPG (148.7 KiB) Viewed 3958 times

The entire ell was stretched and deformed.

GEDC0511.JPG (155.48 KiB) Viewed 3958 times

I'm waiting on materials for this... It's sch. 5, and not something Southern Pipe stocks. McMaster doesn't even have it. Should be here Thursday. Until then, I'm beginning the investigation of another vacuum leak. Also an inner leak.

I love this stuff.

Steve S

[weldin mike 27]

Hey,

Could it be possible that they bashed hell out of it to try and gain more access behind it for welding? Or just somebody when all incredible hulk on it?

Mick

[Otto Nobedder]

No. The root cause was more complicated, and subtle.

[Otto Nobedder]

The sharp dent in the ell was from contact with a reinforcing member of the outer vessel, caused by the inner vessel moving forward.

[Otto Nobedder]

The longitudinal support for the inner vessel is tied directly to the center of the rear head of the outer vessel. The rear head was opened in several places, and welded back up. The rear head was also removed entirely and reinstalled. In each case, the repair welds caused "draw".

I measured the depth of this head, using a 4' level and a tape, and compared it to six other similar vessels here. This head had shrunk by 1 1/4" relative to the others, moving the inner vessel forward by the same amount. This wedged the pipe I showed in the pictures against a support in the outer vessel and caused the damage.

[weldin mike 27]

Hey,

Thats a interesting thing to happen, Are the inner vessels "floating" . For want of a better word. If so is that to deal with the expansion and contraction?

Mick

[Otto Nobedder]

Exactly. The inner vessels are fixed at the closest practical point to the piping that exits both vessels, so the piping sees the least stress possible. The rest of the inner vessel is free to expand and contract with the temperature cycles it sees (though in normal service, the inner vessel spends five years at a time at -423F, only returning to ambient for "retest").

[weldin mike 27]

Hey,
Must be some big brains designing those set ups so the whole thing "works"

Mick

[Otto Nobedder]

Unfortunately, I encounter many cases where the small-minded have worked on them, making my job harder, and sometimes more interesting. It doesn't help that the manufacturer considers every last detail to be confidential information and won't surrender a drawing, despite the fact that they are OWNED by our client.

Steve S

[weldin mike 27]

Hey,

I was going to say " designed by big brains, worked on by some pin heads" judging by some of your photos. Not yours of course being all Yoda like and all. lol
Mick.

[delraydella]

How do you find out that something is wrong? Do they bring the trailer to you knowing it needs work or do you find problems during routine inspections?

[Otto Nobedder]

It usually comes in with a known problem.

When a trailer loses vacuum, whether from an internal leak of product, or an external leak of atmosphere, it loses about 90% of it's insulating ability. The pressure will rise, and the tank will begin to "sweat" like a glass of iced tea on a humid summer day. If it loses enough vacuum, the outer vessel will actually frost over.

There's a large pressure gauge placed where the driver can see it in his mirror, with critical pressures highlighted in neon orange so he can detect a problem. When a vehicle fails on the road and must be vented down (or, worst case, the emergency vent system does it automatically), it's considered a Haz-Mat release with fire dept., police, and company emergency response team. The highway is shut down in both directions. It's rather expensive, between the emergency services and state and EPA fines.

Don't ever hit one of these things... You don't have enough insurance.

Steve S

[Otto Nobedder]

Got my parts.

Challenging weld of the day:

GEDC0534.JPG (210.35 KiB) Viewed 3931 times

Steve S

[Otto Nobedder]

"Cold-shocking" the welds.

GEDC0541.JPG (186.48 KiB) Viewed 3924 times

I bagged the new parts and their welds with aluminum foil, and tacked a "chute" in place. I slowly poured three gallons of liquid nitrogen on all the new parts, and left it to evaporate. The point is to abruptly shrink all the new metal and stress it in a way that is similar to it's normal use. (Three gallons because it boils violently until everything gets as cold as the nitrogen, and I wanted some to sit for a few minutes.)

It was three hours before all the frost melted and I could re-pressure the vessel. I then pressured to 55 psi, and introduced helium to the pipe through a flowmeter, and used a "sniffer" on the mass-spectrometer to sense whether there was leakage or not. It passed, and I began the painfully tedious process of "superinsulating" the pipe. I'll finish that tomorrow, and begin closing the outer vessel.

Steve S