How Difficult Is a Fluid Tight Weld?

[Iplayfarmer]

How likely is it that a self taught amateur like me could weld a container to hold fluid?

I'm self taught, and I'm comfortable with the structural soundness of my welds. Now, I am considering building a backhoe frame with a portion of the structural elements doubling as a hydraulic fluid reservoir. I've never tested any of my welds for "water tightness". Is this something that I could likely do or is it the exclusive territory of skilled professionals?

 

[mustangsallysdad]

How likely is it that a self taught amateur like me could weld a container to hold fluid?

I'm self taught, and I'm comfortable with the structural soundness of my welds. Now, I am considering building a backhoe frame with a portion of the structural elements doubling as a hydraulic fluid reservoir. I've never tested any of my welds for "water tightness". Is this something that I could likely do or is it the exclusive territory of skilled professionals?

Weld it up and and pressure test it with air...that's what I always use...you can even use a guage to see if it drops any.

 

[Transit]

Weld it up and and pressure test it with air...that's what I always use...you can even use a guage to see if it drops any.

You want a continuous weld bead without gaps or porosity. If there is a leak, grind the spot and re-weld. :thumbdown:NEVER leak test with compressed air, fill the tank with water and test for leaks. NEVER, NEVER test with compressed air---BOOM!

 

[mustangsallysdad]

You want a continuous weld bead without gaps or porosity. If there is a leak, grind the spot and re-weld. :thumbdown:NEVER leak test with compressed air, fill the tank with water and test for leaks. NEVER, NEVER test with compressed air---BOOM!

Safety Police Alert!!! Seriously, it only takes about 10 PSI to vessel test...done it for years...if there is an explosion concern use a 5 PSI pop-off valve...I would rather take my chances with 10 PSI air than deal with the water contamination. You use compressed air to check for a leak in a tire, don't you? Not much difference if you use common sense.

 

[Yankee]

As long as you're talking sheet metal and low pressures, pressure testing is fine. Every welding school in creation does it.

 

[RickB]

I'd vote against using a structural member as a reservoir regardless of your welding skills. The long-term probability of leakage due to flexation and cracking is just too high. There are lots and lots of Ford 730 and 735 loaders and other brands & types of loaders in this world with oil in the frames, and many of them weep fliud at high stress points. Once you get a crack permeated with oil, it's a chore to get it clean enough to weld up fluid-tight again.

 

[Egon]

How Difficult Is a Fluid Tight Weld?

It all depends on skill level. For some it's all in a days work. For others it may be classed in another category of weld.

In actuality its more about a proper weld than just being fluid tight for a short time.

 

[pat32rf]

A proper weld IS fluid tight. In most cases its just a case of taking the time to clean the joint and watching the puddle, not the arc. If you do wind up with a leak, grind it down instead of trying to patch the weld....
I started my welding by sticking two pieces of angle iron together to build shelves and patch broken "things" around my workshop. Then I found myself making "temperary" repairs on electric water heater tanks, the 400kw 416Volt variety that we had in apartment buildings. These were classed as pressure vessels due to their physical size and as such were supposed to be done by a licensed welder and then inspected.
In our case the building owners couldn't wait the 3 or 4 days before restoring hot water to 500 tenants so I went in with my buzz box and some 6011 to get the hot water back on that day. Then we would order a new vessel which often had a 90 day delivery

 

[towmotor]

I wouldn't say there's "nuthin to it", but if you lightly pressurize the vessel (like someone already said, 10 psi is plenty) you'll be able to spaot any leaks with a bit of soapy water.
I've also used vacuum to check for air/fluid tightness, but that will only tell you if there's a leak, not where, so it's only good for checking small welds, like a pipe nipple into a tank or something.

 

[dfkrug]

Once you get a crack permeated with oil, it's a chore to get it clean enough to weld up fluid-tight again.

This very important, and why I always test a welded hyd fitting with
air, as when welding a fitting onto a cylinder. I am no expert, so I do
get some micro-porosity is some of my MIG welds, detectable with soapy
water. If oil-contaminated, the weld will have to be cleaned with a
solvent to get all the oil out of the nooks and crannies.

 

[Iplayfarmer]

Thanks for the replies. You've confirmed what I suspected...

A fluid tight weld doesn't require special skills, it just requires good basic skills.

I'm not sure I'm confident enough in my welding skills yet to count on it. If it were going to hold any kind of pressure I'd avoid it. Since it's a hydraulic reservoir with a vent to atmosphere, I may be willing to try it. The low pressure air test is a good idea I hadn't thought of. I guess I could weld up the piece and test it. If I can't fix all the leaks, then I can go with plan B, a bought reservoir. Are there any tricks to getting a good tight weld?... More heat? Multiple passes? MIG vs. Stick? (I have both.)

The discussion may be purely academic at this point since I calculated the volume of the space that I was thinking of using to be about 1.5 gallons. I'm using a 9 gpm pump.

 

[mbohuntr]

If your mig welding Hot Rolled Steel, it wouldn't hurt to grind off the mill scale first. Same with galvanised or rusty steel. Mig is pretty sensitive to dirty metal, worn tips and liners, as well as wind. If in doubt, run it a little hotter than you think you need. More penetration isn't a bad thing. Also, make your resevoir big enough so the fluid gets a chance to cool off. A small resevoir will get hot faster since you will likely be making an open center system. (The fluid is continuously pumped) Open (outside) corner joints are typically the easiest to make tight because you are exposing the most base metal to the arc. If you get a pinhole, hit it with the grinder, then spot it with a stick welder. Test with only water or air... Hydraulic fluid can flash when vaporized by welding. Lastly, make sure you put a filter before the pump so dirt doesn't ruin it.

 

[patrick_g]

While waiting to achieve the level of skill required to do air tight or water proof welds I found that a little flux and some brazing rod tended to make a leak go away.

Pat

 

[Iplayfarmer]

While waiting to achieve the level of skill required to do air tight or water proof welds I found that a little flux and some brazing rod tended to make a leak go away.

Pat

I had also thought about using the acetylene torch to touch up the pinholes.

...Also, make your resevoir big enough so the fluid gets a chance to cool off. A small resevoir will get hot faster since you will likely be making an open center system. (The fluid is continuously pumped)...

I will be using an open center system. That's why this reservoir will likely not work. I think the rule of thumb is to have the reservoir equal to the gallons per minute. I.e. my 9 gpm pump needs a 9 gallon reservoir.

 

[mbohuntr]

If memory serves, Mine had a 10 gal. reserve, a 2" cylinder, and a two stage barnes pump. I could run it on a hot day without worry. We did quit using snowblower engines as they burned up by running too hot.

 

[Car Doc]

I do it all the time its no big deal as long as you arnt welding upside down and backwards haha!

Its really a matter of getting the area clean and grind as necessary and make multiple passes where you can see what you are doing and air check with soapy water in a spray bottle.

That said why do it inside the structure I would be very worried about stuff happening or contaminants?

Steve

 

[Transit]

While waiting to achieve the level of skill required to do air tight or water proof welds I found that a little flux and some brazing rod tended to make a leak go away.

Pat

Yes, thinking along the same lines only with solder as a seal.:thumbsup:

 

[Scotty370]

IPlay- I built a tank for a log splitter years ago by O/A welding some 1/8" plate to each end of a 24" piece of 6" pipe. I also burned a couple 1" holes in one end of one of the plates, (side by side, at the six o'clock position) and cleaned and welded 3/4" pipe couplings, for inlet/outlet fittings. Worked fine after I ground and spot-filled some pin holes with brazing rod. In your application I'd be concerned that the flexing created in a 'structual' member would crack any weak spots, in short order! ~Scotty

 

[patrick_g]

Worked fine after I ground and spot-filled some pin holes with brazing rod.

Glad to see I'm not the only one brazing welds to get them pressure tight. I don't feel quite so inadequate now.

Pat

 

[Scotty370]

Glad to see I'm not the only one brazing welds to get them pressure tight. I don't feel quite so inadequate now.

Pat

Pat- My motto "If ya can't be perfect, learn how to cheat!" :laughing: