Welding Tips and Tricks

Here's my view inside a liquid hyrogen trailer. Less to see than I expected...

well, it's not something you see everyday, that's for sure.

is that the fill gauge apparatus in the middle?

I have seen similar

Why doesn't the trailer have baffles?

I sell diesel and routinely see inside of tank trucks and once the compartment is over a certain size, it would have in a baffle. That trailer looks to be about 5000 gallons and in the fuel business, it would have 4 to 5 baffles inside of there. Tank trailers or trucks fall under DOT 406 spec.

What spec does liquid hydrogen tanks fall under?

Delraydella,

The pipe in the foreground is vacuum-jacket, containing two 3/8" pipes. One WAS the full-trycock line, as a fill indicater, as you surmised. These have been sealed (epoxy-injected), as they were subject to breakage. The other pipe was, and still is, the vapor-phase signal to the liquid level gauge. In the background is the vapor leg going to the top of the vessel (with about 10" cut off for access), a 3" pipe used for vapor recovery, and the main safety emergency vent system. The trailers are now filled using a metering system, and then a weighing for confirmation.

Fargo,

The I.D. is 90". The capacity is 13,487 gallons.

The reason there are no baffles is that 13K gallons of liquid hydrogen only weighs about 7400 pounds and has a low moment of inertia.

Otherwise, they fall under the same DOT req.s, except for ASME vessel retest. There is an exemption that allows the pressure retest to be done at 1.25X MAWP, where most vessels are tested at 1.5X. This is due to the high vacuum between the inner and outer vessels. (When the inner is open to atmosphere, there is still "one atmosphere", or about 14.7 PSI pressure difference between the inner vessel and the evacuated space.)

Otto, I have two fears. One, heights. Two, confined spaces. No amount of money could get me to work in an environment like that. When I'm in an enclosed space, it feels like the walls are pushing against me.

Anyway, I've done some repair on some electrical motors and some other stuff. Since I now can weld, I'm thinking of making my own generator. I know where to get a gas engine and can build a killer platform. But, I need a power head able to produce a minimum of 50 amp for my buzz box. If you could point me in the right direction, I would greatly appreciate it.

Craig,

I've known several people who couldn't do confined spaces, for the reason you mentioned. I've only known one who learned to override it. Notice I didn't say "conquer" it. He was never comfortable, but he became able to handle it.

As for the power head you're seeking, I'm not sure where to direct you. If I were making the search, I'd look on E-bay and similar for existing machines being sold with "engine trouble". Buy the whole damn works, and put your motor on it, for a song.

Just speculation. Your mileage may vary.

Steve

Craig,

You can usually find dead, dying, or maybe running generators for parts on this site...http://gsaauctions.gov/gsaauctions/aucitdsc/

look under "Electrical and Electronic Equipment and Components" also try under "Industrial Machinery", sometimes there are a few there.


Steve

I'm the same way when it comes to confined spaces. If the end was open, no problem, but close it in or if someone gets between me and the opening way out....I'm done.

Try checking your local metal recycler for generator power heads. I see so much of this stuff get scrapped because people cannot be bothered to repair it, or simply do not know how to repair it. We live in a throw away society and there's lots of perfectly useable products sitting in the recycle yards, just waiting for someone to retrieve it. Typically, I would pay no more than 5 bucks in a recycling yard for a generator. (10 cents per pound is average.)

CraigLam wrote:Anyway, I've done some repair on some electrical motors and some other stuff. Since I now can weld, I'm thinking of making my own generator. I know where to get a gas engine and can build a killer platform. But, I need a power head able to produce a minimum of 50 amp for my buzz box. If you could point me in the right direction, I would greatly appreciate it.

Hey guys, the response is great. The recycler is a good idea. This is actually gonna take some time. I saw on the internet, that some guy took a car regulator, and hooked it up in such a way that the amps it generated was used as a welder. Then I started going down that road and other sites had it as well. But, there's no schematic. I'm trying to get hold of an electrician who would know how to do this. I saw one with a battery. The amps in the battery are about 300 amps, but , that wouldn't hold when you started to weld. I would think that the amps would drain quickly and take the alternator a long time to recharge the battery. As you can see, I'm not too literate when it comes to electrical.
Power heads were impossible to find. I checked everywhere. The best thing is to wait 'till I see a used generator for sale on ebay. They had 15KW generator for sale for $1600. Not too bad, but, local pick only. If I build my own, I could do it for half the cost.
Anyway, thanks for the help. I'll keep looking.

I found it, I found it, I found it! I came upon a web site, where a man was in the process of building a homemade generator. Like me, he didn't know alot, but, from his explanations, he knows alot more than I do. He took a gas engine and an alternator/generator and designed a platform to mount them. So far, I got that. However, he explains that a car alternator is not good to use. It's to expensive and will not produce the current I need. He also explained what three phase is. I never new that. I know that there are three wires that are hot. But, he explained it perfectly. How three hot wires share the load instead of one. Instead of one turning 360 deg., a three phase turns 120 deg. (3x360) and delivers more power. Best of all, you can get them cheap. Companies actually throw them out. Thy're too expensive to rewind, so they toss them. I looked on ebay, and I can get a good one for about a hundred bucks.
Anyway, I'm gonna contact an electrician to find out how to build a control panel with all the proper components. To be continued......!

any spinning electric motor will generate power. Our shop has a lot of 3 phase machinery but we don't have 3 phase coming into the shop, so we use a "rotary phase converter" which is basically a 3 phase motor and a motor starter. Depending on the total horsepower needed for however many machines you are running at one time, that is the size motor to get. Always go over on size.

It is important to note that although those devices generate 3 phase power, it is NOT pure 3 phase power. That means that the legs don't fire at an exact 120 degrees apart so you won't get the rated horsepower from whatever machine it's hooked up to. You can expect anywhere from half to 2/3rds of rated horsepower.

Steve

Made progress Friday. By damming the rear third of the compartment, I've significantly reduced the "search area".

Steve

My knowledge of three phase is limited. However, I do know you have to have three phase power coming into your building from an outside source. Anyway, tomorrow is Monday and I'm gonna find an electrician that can draw me a detailed schematic of what I want. My mig welder is nice, but, I still want to be able to use my buzz box. I still think stick welding is the ultimate.

No, Craig,

They make "phase converters", as delraydella said. The simplest is a single-phase motor coupled to a three-phase aternator. Had one of these that would support 7.5 HP in this little back-woods shop I worked in 25 years ago. These should be avaiable used, and possibly military surplus. They're more of an industrial item than home-shop equipment, though I suppose they were available in smaller sizes.

There are also digital ones based on inverter technology, but I doubt I could afford one.

I've never needed one, so I don't know where to look other than starting with google.

Steve

http://www.phase-a-matic.com/

they are usually available at industrial supply stores like Grainger or Production Tool
check Craigslist, too, there is usually someone out there who builds his own for a fraction of the cost of a Phaseamatic, but you won't get the service that you will from a professional supplier.
Static phase converters are listed by whatever horsepower motor you need to start. A rotary phase converter can be any horsepower depending on what horsepower the motor is that is generating the 3 phase power.

Static phase converters should never be used for any type of CNC machinery or any type of machine with a heavy starting load. Any type of machine with electronics should not use static converters.

Rotary phase converters can generally be used for most types of CNC or electronics, but not all. You have to check with the manufacturer to see if a rotary or an electronic phase converter is needed.

Depending on your power needs,Static converters generally run from $125 to $500, a rotary will run about $500 to $2500+ and an electronic one will usually start in the several thousands of $$$.

Steve,

I use a VFD (Variable Frequency Drive) in my home basement workshop to drive my lathe. It takes the 220VAC single phase incoming power and converts it to a variable frequency three phase output which I use to turn the three phase motor of my lathe.

It is extremely efficient and has sixteen programmable speeds that can be assigned to push buttons, plus a full analog speed control knob (for fine speed adjustments). It also features a programmable two speed spin up and two speed spin down system so that the mass of the work piece is managed in a very effective way.

There is a thermal shut off switch so that the motor won't over heat and an optional shut down switch that can be anything that you want it to be. I use a vibration switch, so that if the work piece becomes unbalanced, the system shuts down for safety purposes.

http://www.hitachi-america.us/products/ ... ves/l100m/
http://www.youtube.com/watch?v=aTwPsxS5h6I
http://en.wikipedia.org/wiki/Variable-frequency_drive

Otto Nobedder wrote:No, Craig,

They make "phase converters", as delraydella said. The simplest is a single-phase motor coupled to a three-phase aternator. Had one of these that would support 7.5 HP in this little back-woods shop I worked in 25 years ago. These should be avaiable used, and possibly military surplus. They're more of an industrial item than home-shop equipment, though I suppose they were available in smaller sizes.

There are also digital ones based on inverter technology, but I doubt I could afford one.

I've never needed one, so I don't know where to look other than starting with google.

Steve

Hey there,

Back on topic, does a hydrogen tank need to be cleaned out before you weld on it as per any other flammable liquid?

Mick

I thought about the same thing Mick

In my line of business, gasoline tanks would have to be steamed out to remove any residue before any repairs. But diesel tanks can be repaired with fuel in it once (no liability accepted) the diesel level is below the repair and the fuel is blanketed continously with CO2. TIG welded of course to remove any chance of pinholes(small leaks)

I have heard of an instance where a diesel tank that was full of fuel and the outlet broke off the tank ahead of the first valve just leaving a open hole in the side of the tank. The owner of the tank stick welded the outlet back on to the tank with diesel actually spouting out as he was welding.

We do not perform hot-work of ANY kind on a trailer that has not been purged to nitrogen with a measured outlet temerature of at least 52*F, and we verify with LEL meter that the H2 level is below 1% before it's even allowed in the shop. The lower explosive limit for H2 in standard air is 4%.

H2 boils above -423F, so by the time the vessel reaches ambient temp, the liquid is long gone. All that is left to do is purge any remaining gas. Our primary customer takes care of this (on the inner vessel and all piping) before we recieve it, so all we normally have to do is verify it before bringing it in.

For an inner tank leak, however, the annular space (the space between inner and outer vessels) may have a nearly pure hydrogen atmosphere, which we must purge outside in open air until it's safe.

Unlike petroleum products, Hydrogen does not leave a residue to clean.

Steve

BTW, today I narrowed the leak to one of two welds on a 6" pipe.

To my irritation, I can't "put my finger on the leak" without major surgery. The pipe that is leaking is not process piping, it is the rear, curb-side main tank structural support, so I have to open the outer vessel below, and support the inner tank before I can remove the structure that's in the way of further location of the leak.

The boss handed me this job because I like a challenge... Truth is, I like some more than others.

Steve

Good stuff thanks for info.

Mick

Hey, guys, I'm moving this over to stick welding. Keeping this on topic is correct. See you there.

Yesterday morning, about a half-hour before the test disproving a second leak on the roadside tank support, the mass-spec took a crap. $30,000 tool took a crap while I'm using it. So I'm on hold until the replcement arrives Friday, and won't be back in the tank 'til Monday.

Damn!

Steve S.