Welding Tips and Tricks

Steve,

That's not the same repair... This one was crushed by it's own insulation.

On the hydrogen trailers, there's virtually nothing considered beyond repair, due to replacement cost. Not so for the liquid argon trailer in the most recent discussion. The time spent was to create a "condition report", which defines what fixes are needed to keep it in ASME code. We'll create an estimate, and the "Rehab Coordinator" will decide whether the cost is worth the remaining life of the trailer.

Steve S

"That's not the same repair"

Here, finally, is a better pick of the buckling, with two of the leak locations. The leaks, as expected, were in the welds, at the "creases".

Here's one of three baffles I had to climb through to reach the damage;

That's a plain roll of paper towels sitting in the manway.

I would be haunted by those holes every time I went for the 2nd plate at dinner and especially holidays. I guess at some point if your pants still fit like they should, all is well.

This project is in "stand-by", as I now have what I need to get another out the door, and am working on the weldout.

Once this project hits it's long-term shop spot, though, I'll have interesting pictures. I'll be cutting and removing the front 8' of the outer vessel to access this.

The mechanism that crushed it is interesting... As an older atmospheric trailer, it is insulated with vacuum and Pearlite, a fine mineral compound. Each time the vessel sees product, it's temperature drops (I have to look up liquid argon temperature), and pearlite fills the empty space when the inner vessel shrinks. When the product is gone, the vessel expands, and compresses the pearlite. Many cycles of this, and the pearlite can compress no more. The tank expansion pushes back on itself, and you get crushing, like mashing a beer can.

Steve S

I am familiar with perlite as a soil conditioner in it's expanded state. At a glance, it looks like something a bean bag chair might be filled with.

I never thought about how much these tanks would expand and contract.

I can't wait to cut this thing open! Of course, there's much prepwork. I need the bogie (The end with the wheels) dead-level, and the pick-up plate dead-level, so when I put it back together, everything will be level and square. The pick-up plate, the semi-trailer equivalent of a hitch-ball, must be level, but it's part of what I'm removing for the fix.

Steve S

Well, back to the project with all the cracks. Went with 304, rather than 316, simply because changing from original material requires a very lengthy, annoying, and expensive EMOC (electronic management of change) process.

Here's the replacement section and end-cap welded out: Welded in the end cap on the bench... That was nice!

The 5g was much tougher than I anticipated, for the root pass at least. That 37* bevel forced me to jamb my head against the vessel tightly to see both lands and the backing ring. I'll have sore muscles tomorrow.

It goes back on the vacuum pump tomorrow, and I can start proving all my repairs with helium leak-testing.

Steve S

Hey,

I can see how it fits together now. Is there a particular reason for this little protrusion from the vessel ?

Mick

Yeah, Mick,

It's part of the structuaral end of the "longitudinal support". I've described these vessels as "thermos bottles", with one vessel holding product, and another, outside it. This support part of connection between them.

When it's complete, there'll be a lot of gussets and structure tieing this new metal to 75% of the rear head, to spread the load of the cargo.

Hey,

Sweet as, this is where the wagon wheel (?) thingie welds on? If it is i can see now why it cracked?

Mick

Yep.


Here's a complete "wagon wheel" on a similar trailer. I found some evidence in that Avesta welding manual to support the theory that chlorides are the root cause, with the stresses this part sees leading to the ultimate failure.

Steve S

Hey,

I feel silly now. I can see exactly what is happening now! I could see the forrest for the trees before

MICK.......

Did the helium leak test this A.M. under full vacuum, and verified the inner vessel repair at the same time. All came out good, so I broke vacuum and began fitting the "spokes" of the wagon wheel, the "T" gussets in the other picture.

I got all the templates made (with a repair like this, with so much previous work, I was relieved that two templates fit four locations, so I only had to make two unique parts), and the 6 o'clock "spoke" in and welded.

For templates, I was carving corrugated plastic sheet (free from the neighboring business) with a utility knife, scribing it to the exact profile, and trimming for a good fit. Tomorrow, I transfer the templates to 1/4" SS sheet and plasma-cut them.

The 4" flatbar caps are easy... I rigged up a simple jig to draw the inner radius with a compass, and can scribe the outer radius once the inner fits.

Steve S

Road salt can do some damage!

Here it is, back together. It's spending the weekend on the vacuum pump and inner-vessel heat to drive off moisture from being open so long.

I'll have some findings on the fix Monday evening.

Steve S

Okay, here's that crushed tank on the Argon trailer... Steve S

Here it is, sectioned out, preliminary cleaning (old welds ground flush), and it sprang back into postition, and a little beyond, exactly as expected. The new section is being cut to width and rolled to radius (left long) at our manufacturing facility in TX. There will be no backing bar. Once fitted and tacked, it will be TIGged from the inside with an argon purge dam on the outside (two passes), then back-ground from the outside and finish welded (2 passes) from the outside, with an argon purge-dam on the inner. The fun part is the inner will be done with an ESAB Miniarc 90i, 'cause it'll fit through the obstacle course, but it's air-cooled and scratch-start.

Steve S

Very Cool! You have a very interesting job!

When you pulled off the back of the outer tank, did you have the attachment points for the lift slings already on the tank or did you have to add them on?

There are Praxair and AirLiquide facilites not too far from where I work so their trucks are always going by us. I pay a lot more attention to their trailers now than I ever did before...

Hey, Steve,

If you look back to the post showing the nose on the ground, you'll see the single sling in a shackle, with a row of lifting-eyes. This was added. I was not consulted (they were trying to stay ahead of me on the "general" work), or there would have been a single pad-eye right where the shackle is in the picture, only rolled about 2" to the left, rather than top-dead-center, as some auxiliary structure makes the left heavier than the right, so it rolled slightly as it came loose.

Through the whole process, the boss, the manager, and the supervisor were trying to second-guess my placement for the shackle and sling, and I think they were annoyed that I kept saying, "I like it where I put it." It shut them up when it finally came free, and was hanging almost dead-level. That's my industrial experience coming through, though. One shot to put the pad-eye(s) where I want them to make the load hang where I want it so I don't have to fight it. Fortunately, the foreman listened, and had one of the eyes placed directly over the pin of the fifth-wheel hitch below, which is the one I chose. I'll relocate it to the left when it's time to re-hang it, so I don't have to fight to line it up on the circumference. Or maybe add a pad-eye low on the left I can put a come-along on, to pull it into alignment in "roll".

As interesting as I find my work, today was a long day. Jobs like this have their share of mundane bullshit, and I had a handfull today. Dragged leads, hoses, and cords, placed equipment, replaced a couple of overhead pipe supports that were broken, and then layout work for reinforcements for other minor buckles inside this sucker.

Steve S

Today was an interesting day!

I discovered two failures I NEVER would have thought possible.

One is in a critical safety system. It's a pressure switch to close a valve in the event the pressure rises above 45 PSI (the MAWP on this one is 50 PSI). It's designed very carefully so that it only has a "fail closed" mode, meaning that any conceivable falure in any part of the system will close the valve to prevent too much pressure from building, on a liquid hydrogen trailer. A failure to close this valve would be catastrophic, and possible if the operator were incapacitated for some reason. I mean "Timothy McVeigh" catastrophic.

I discovered a "fail open" mode. This was an older model pressure switch, of which many are still in service. The adjusting screw has a locknut, rather than the "nylock" style on the newer models. It require tiny ignition system wrenches (in 1/4") to adjust and lock. The last person to set this switch apparently had standard wrenches (too fat for the job), and felt the need to add some red lok-tite to back up his work. This ran down the shaft into the actuator, and locked it in place. It's been like this for five years.

I expect I'll be visited by the client's chief engineer again...

The other failure I never thought possible was a simple cracked shaft on a manual valve. One would expect this to happen from time to time, with the risk of the valve shaft breaking off. Not this one, it caused a leak. A picture will do more than words, here. Note the dye-penetrant: As I said, an interesting day!

Steve S

Hey,

Sounds like one of those " If you really knew what was happening out there, you would never sleep again" Moments.

Mick

How long does i take you to weld one of those seams all the way around?

Good question, Jeff.

Two passes from "IN", backgrind, and two passes from "OUT". Aprox. 25' each pass, TIG all the way.

I'll have to log the time, so I can eventually answer.

I should add, I never encounter a "typical" situation, where I can answer off the top of my head. These cases have been unique.

Steve S