Welding Tips and Tricks

I'm re-assembling after a repair. The toughest leak I've ever chased, because it would not leak below 30 PSI internal pressure with vacuum present in the jacket. I ended up having to cut this whole assembly into jigsaw pieces and pressure the inner pipe with helium to 150 PSI to get to the root of the problem (a factory-original weld, and the absolute end of the piping, so if the coin-flip had gone "tails", I'd have STARTED at the problem, rather than ending there...)

The picture shows every aspect of a vacuum-jacket (this section is at the meter pick-ups, thus the complicated legs), including the inner pipe, the mylar/tissue "superinsulation", the fiberglass tape overwrap (both to hold it all tight and to protect the mylar from welding heat), and the safety wire used to hold everything together.

This assembly is just tacked up at this point. The last bits were tacked in today, but I took this pic first so the layers would show. I have a full day welding this section up, then it must be mated with the section I cut it from, then bench-tested, then the whole assembly reinstalled in the trailer. Probabaly 40 hours, and than I have to test and prove every inch. Steve S

Steve,
You have your work cut out for you. Leaks like that would drive me crazy. I wish you were closer, would love to shadow you for a day. For the bench test, how long will you pressure it and to what psi? If you can, get us a pic of the finished welded piece.
-Jonathan

I agree it would be cool to watch him work seems like fun and tedious all in the same how does one land in this line of work

The bench test won't happen until this piece is reattached to a larger manifold it was cut from, but once that is done it will be helium leak-tested at ambient pressure for the external piping, and I'll pressure the internal to 225 PSI. (MAWP is 150 PSI)

I've never dealt with a leak like this, that refused to demonstrate until pressurized. It gave me fits. I bet I have 40 hours in "putting my finger on" the leak. It usually takes less than eight. I've only had one that was more frustrating, and it took me about 120-160 hours. It was an inner vessel leak, in a form no one in my field had experienced, so there was no good advice to be had.

I'll take some pics as this goes back together, to put it all in context.

Steve S

JDIGGS82 wrote:I agree it would be cool to watch him work seems like fun and tedious all in the same how does one land in this line of work

That's a great description. It can be great fun. It can also be hours of just standing there watching a machine, waiting for it to tell you something useful.

I have no idea how to land a job like this. I've searched, just to see... to compare what I make with what's offered. Can't find my job. No one seems to offer it. I know it exists (not just because I do it), they sell the damn equipment for it. I can get parts for the machines.

I can't even find a "Department of Labor" classification for it.

By the way, I "fell" in to this. It was something that needed done where I work, and I showed an unusual ability for it. Now, it's mine, whether I want it or not...

Steve S

Okay, an update.

Here's definite proof I don't get nearly enough hood-time. (Granted, the cuts were on existing welds, so the thickness was constantly varying, but if I were under the hood every day...) And here is the part, back in the manifold: Here's the root pass for the sch.10 inner pipe... better than my work on the sch.5 Steve S

I stood it up, and did the the cap in 2G, and wish I'd done the root this way. The root came out fine, but I wouldn't have had to stand on my head for the bottom in the 5G. I modified the vacuum jacket for better centering of the inner pipe, which will make the next round of fitting interesting. It may be easier to "stovepipe" it, rather than fit it proper. The original pieces are now scrap, but it will be a better product when done.

Steve S

Steve,
It's going to take a lot of re-vamping to get that to fit up to that O2 trailer. It must be nice to work in a place where the garage walls don't need 6" of insulation, at least until summer.

BTW, I thought there was not going to be any more pictures. I for one am glad you're disregarding that rule. This way I know if I need to worry or not when the LHY driver opens his valves.

Len

Len, while this trailer was built by LOX equipment, it's actually an LHY trailer.

Never seen a lox-built LHY trailer before.

This was going to be the "guess the trailer" I mentioned to you a month or two ago.

There is seriously sloppy work here, at least in the vacuum-jackets. Just in the section I opened, I found two places where the inner and outer were in contact. Bad fitting...

This client doesn't give us a TCR with the details and driver reports, though, so these issues may have been either overlooked or not relayed to us. It must have been at least "sweating", if not frosting, in two places.

Steve S

Steve,
The trailer in the picture is a LHY trailer?

Len

No. The trailer in the background is an O2 trailer, unrelated to the pipe work in my pictures.

Just eye candy...

Steve,
That's the one I was joking about needing the re-vamp work. You had me worried that I was losing my eye for trailer I.D. The engine cabinet with the PTO handle had me wondering what it's use would be in LHY delivery. Now I feel better.

Len

Len,

I wasn't think at all about the fact there was a lox atmo trailer in the background in any of those pictures.... Your confusion makes perfect sense. I should pull that picture down, with our new masters and the photo rules, but I think I'll leave it. I don't see any of their security trolls checking this site.

Steve S

I hope they're not checking this sight or else I'm going to owe them a lot of time. I'm on here almost all the time I'm working, checking in as I pass the computer.

Who would have thought that someday two guys doing work for the same company a thousand miles apart from each other would be chatting like we're in the same building, wild.

Len

It is wild.

And pleasant. I so often have to explain terms like "cryogenic", "superinsulation", or "annular space". Not so much here, since those who are interested pay attention and ask questions.

But, since the word, "Cryogenic" appears on my uniform, I've been asked at the liquer store if I "freeze stuff". Like I have Ted Williams' head at work...

Just between us, do you?

I work with mostly younger guys fresh out of the Navy and find myself explaining everything to them about all things mechanical, they only know the computer and paperwork. They're convinced that it's the actual work and are offended when they're required to physically do something.

I kinda miss being in the truck shop and building things, but the guy I had to work with is a nightmare. Him I don't miss.

If I were single I probably would be working in your neck of the woods. There are all kinds of jobs posted for your area within this company that I would be qualified to apply for, but the little woman has a good job here, so I stay.

Len

Tell Mom that you guys are packing up moving South! I'm sure she would get over it eventually

Sent from my DROID RAZR using Tapatalk

Geesh. I bet your days go by fast. I swear I get towards the edge of my seat every time I view one of your projects. I have come across similar scenarios with different equipment and I often think to myself. . .surely there is some sort of space shuttle epoxy we can just dip this whole thing in.

Hey,

The dude on Myth busters did that exactly thing. Put a pipe system under vacuum and put glue and high strength epoxy on the whole thing. (granted the welds were dodgy as, and if he had welded it properly or brazed it, it would have been fine) but there you go.

Mick

TamJeff wrote:Geesh. I bet your days go by fast. I swear I get towards the edge of my seat every time I view one of your projects. I have come across similar scenarios with different equipment and I often think to myself. . .surely there is some sort of space shuttle epoxy we can just dip this whole thing in.

Actually, there IS one place we use epoxy.

The main vacuum valve, used to evacuate the annular space, is usually threaded, and we use 3M epoxy to seal that joint. In the past, these were brazed, but that makes replacement difficult (we encounter faulty castings and other issues requiring replacement). With epoxy, a good "cook" with an o/a torch, and we can unscrew the valve, clean the threads, and install a new one.

Steve S

Well, here's the section I thought I'd be stove-piping, but I tossed all the original pieces, and cut up some 4" sch.5 scrap. So I was able to take measurements and actually fit it, cutting down both fit-up and weld time. As you can see, there's one section of "clamshell" yet to tack in place.
I got the weld-out finished, and put this manifold under vacuum today. I have (at least) one small leak, which doesn't surprise me. Even parts of the salvage material were cut on existing welds. Frankly, I'll be surprised if there's only one leak. Cant worry about that too much, though, this project's on a short hold as I have six code welds to deal with tomorrow and Wednesday.

Steve S

Well, here it is in it's native habitat. Sorry for the fuzzy pic.

I welded three sections of vacuum-jacketing this AM, and fit it back in it's home, then welded out the inner pipe. Waiting on some more insulation before I can close the outer jacket and test it as a complete assembly.



And here's the inner pipe welded back to it's origin. The butt-weld, not the socket...



Tommorrow, it gets pressurized to 100 PSI, then a helium flow though it, and a mass-spectrometer "sniffer" test to prove the weld. It won't leak (two solid passes on sch. 10), but I have to prove and document it anyway.

Steve S

Really enjoy seeing these projects. You do a great job explaining the problem, and you're solution.

Every time I see one of these trailers going down the freeway I think of your posts. I had no idea how expensive and complicated these trailers are in real life. Thank you for sharing and keep posting.

Thanks, Wen,

I've done many interesting and different things over the years, but this takes the cake. I've never been bored, and it pays well. This is a job where I'll never stop learning something new.

I like sharing the work, too, though I don't weld so neatly anymore. My eyes are not so good, and my hands shake, so I'm gratefull I can still pass a code test.

Steve S

It sneaks up on us, don't it??