Cracked or pinhole leak in hydraulic steel tube

[DaveK OR]

My Bobcat CT230 (almost identical to a Kioti CK30H) has developed a leak in a cracked tube that connects to the Joystick Valve Assembly. It's the steel tube that connects on the outside of that assembly. My suspicion is that there was a longstanding metallurgical issue that failed when I accidentally deadheaded the hydraulic system (trying to lift a bit too much with the FEL) and a crack propagated through the tube.

Anyway, since Bobcat no longer makes these tractors, and it seems that Kioti has declared the corresponding part to be obsolete, getting a replacement tube assembly may be troublesome, to say the least.

A local tractor vendor has suggested that I have the tube brazed to fix the crack. Does anyone have any insight on this? Can it be brazed to effect a reliable repair? Would it be better to TIG weld the crack? Are there other options I should consider?

It's going to be a somewhat difficult job no matter what, as I will have to dismount the FEL, then remove the right-side FEL mount to gain access to bolts that secure the other end of that hydraulic tube.

Thanks in advance for any advise.

 

[RickB]

Brazing will be effective if done well.

 

[RNeumann]

First goal would be to have a new hose made- even a flex hose would do.

If the end going into the valve is something special I’d braze a new common fitting (IP or JIC) onto the pipe.

Brazing a crack can be done but I personally don’t like chasing cracks with brazing or welding- I’d rather cut it off a put a new end on.

About 15 years ago I silver soldered some fittings onto pipe for the power steering on a vehicle I drive near daily. It has held up fine.

 

[wdchyd]

Any pics?

 

[rScotty]

My Bobcat CT230 (almost identical to a Kioti CK30H) has developed a leak in a cracked tube that connects to the Joystick Valve Assembly. It's the steel tube that connects on the outside of that assembly. My suspicion is that there was a longstanding metallurgical issue that failed when I accidentally deadheaded the hydraulic system (trying to lift a bit too much with the FEL) and a crack propagated through the tube.

Anyway, since Bobcat no longer makes these tractors, and it seems that Kioti has declared the corresponding part to be obsolete, getting a replacement tube assembly may be troublesome, to say the least.

A local tractor vendor has suggested that I have the tube brazed to fix the crack. Does anyone have any insight on this? Can it be brazed to effect a reliable repair? Would it be better to TIG weld the crack? Are there other options I should consider?

It's going to be a somewhat difficult job no matter what, as I will have to dismount the FEL, then remove the right-side FEL mount to gain access to bolts that secure the other end of that hydraulic tube.

Thanks in advance for any advise.

First off, is a tube strictly necessary in that application? Can you replace it with a hose instead? Pressure wise, a hose should be up to the task. And I doubt very much that any hydraulic pipe is ever designed to be part of a structural support. Why not a hose?

But you asked about brazing, and it's something I do a lot of. First off, cracks propagage because the point of the crack has a very small radius - so the loading per square inch goes off the chart at the point of a crack, while at the same time the length of the crack acts as a lever. That's why to stop a crack from propagating it's common to drill a hole at the ends of the crack. You'll do that before brazing. For a half-inch OD thin wall pipe I'd go with about a 3/32 diam. hole. Dimple the spot first to get it right at the end of the crack.

As for tradtional brazing on hydraulic line steel, it can be done with low fuming brass or bronze, or nickle bronze, or silver brazing - all of them will work, and will also fill in the two holes you drilled. Brazing isn't too common today, but most old timers have done a lot of it and will know which type of brazing they feel is right. Done right all of those alloys are more than strong enough. I work with them all. The key is going to be how that pipe looks when you get it off. Does it look swollen? I'm betting not, but look. That's because I wonder if the dead-heading really caused it. Most hydraulics get dead-headed commonly during use, and the relief valve protects the components. Is there a relief valve in that circuit? There almost has to be.

So as to brazing, I'd give it a try - especially since it sounds like no matter what the fix, you are going to have to dismount the loader and open that side. That's just wrenching, so is likely to be painfully slow the first time and pretty easy the second...if necessary.

As for taking off the ends and brazing them to a new tube, it all depends on how accurately you can reproduce the old tube. From your description it kind of sounds to me like the pipe is not straight and accessible. Maybe it has bends and is in a hidden location. That might make it difficult to make another one fit right.....which puts us back to hoses....
rScotty

 

[mrmikey]

I've fixed a somewhat similar problem awhile ago and it's still going, it was ss hyd tubing. I cut a piece of tubing that the ID would match the OD of the cracked tube, cut it a bit longer than the crack, split it so I had a half tube and silver soldered it over the crack. .......Mike

 

[rScotty]

I've fixed a somewhat similar problem awhile ago and it's still going, it was ss hyd tubing. I cut a piece of tubing that the ID would match the OD of the cracked tube, cut it a bit longer than the crack, split it so I had a half tube and silver soldered it over the crack. .......Mike

I think that's a dandy way to fix a crack. The silver solder - also known as silver braze - is very strong and bonds especially well to the nickel in the ss hyd tubing. Drilling the ends of the crack before putting on the patch would make it stronger yet, as would rounding the corners of the patch, roughing the surfaces, and beveling the edges. That's all hand work. I'm betting you probably did some of those tricks, and it wouldn't surprise me if that patched area is now stronger than the rest of the tube.

Some questions: Were you able to remove that hyd tube and clean it before patching? Do you think that's necessary? Did your tube have a threaded compression fitting or did it terminate into a block?
And would it have been possible to replace the tube with a hose? Depending on the ends, I think it might be. It's worth thinking about.

I just love it when people get creative about fixing their old tractor instead of buying a new one. Most every tractor out there was designed and built to last a long, long time. It doesn't bother me that making it last implies some upkeep; that's just part of the fun.
rScotty

 

[pmsmechanic]

I usually replace a metal pipe with hydraulic hose. It's most of the time just easier to cut the pipe into several pieces to remove it than to disassemble all that's needed to remove it. The hose then then be easily maneuvered into place. Also a hydraulic hose absorbs flex where a metal pipe would break.

That being said I've also brazed leaks too. I've never thought of drilling a hole in the end to stop the crack but that makes sense to me.

 

[rScotty]

I usually replace a metal pipe with hydraulic hose. It's most of the time just easier to cut the pipe into several pieces to remove it than to disassemble all that's needed to remove it. The hose then then be easily maneuvered into place. Also a hydraulic hose absorbs flex where a metal pipe would break.

That being said I've also braised leaks too. I've never thought of drilling a hole in the end to stop the crack but that makes sense to me.

It can be a tiny hole. For stress relief the benefits start anytime the drill hole has a larger radius than the end of a crack. That doesn't take much.
For stop drilling a crack in the plastic fenders of my JD, I use a 1/8" or 9/64 drill bit & backfill with silicone sealer. For a crack in the metal hood latch on the same tractor I use a 3/32 drill and backfill with paint. For a gold bracelet where the catch has cracked I use a .050 drill bit and backfill with silver solder.
rScotty

 

[mrmikey]

Were you able to remove that hyd tube and clean it before patching?

Yup, pretty much have to to get rid of the hyd oil in the area, if you don't the heat will draw it out and you'll never get the solder to stick

Do you think that's necessary?

It could have been done in place (as long as I could get it drained properly) but it was at work and it was feeding hydraulics to the rear of a spreader/dump body and wasn't hard to remove with the body up.

Did your tube have a threaded compression fitting or did it terminate into a block?

Both ends terminated in a #12 Swagelock compression fitting to a #12 male JIC at each end. Truth be told, if we'd had the tubing in stock, I would have replaced it but I was too lazy to drive the half hour into town to get a length.

And would it have been possible to replace the tube with a hose?

We could have used hose on the initial build but by using ss tubing and ss Swagelock fittings it was one less area to worry about rust and a hose breaking. The tubing never cracked, it was worn thru by a hydraulic line someone had draped over the tubing aka a clothesline.