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Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

(OP)
All.. help...

Pneumatic Duct [300-PSIG air, 800F]: Inconel 625,'multiple s-turns' duct, 3.0-inch OD, 0.035-inch WT, dents creases due to miss-handling up-to ~0.20 deep. Some of the dents/creases have sharp features [very tight radii at dent center/crease-centerline].

Ideas for restoring tubing roundness? These ducts are $30K/each... last production run... now out-of-production.

What tooling works best and what is currently available? Vendors? Home-made?

Pull/push-thru ball mandrels?

Localized internal [hydraulic?] expansion tools?

High powered magnetic dent-remover [concave outer electromagnet, convex inner permanent/steel?

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

will 300psi pop them out ? maybe use collars on the outside to support the tube and pressurise ?
or something like a car panel dent remover ??

another day in paradise, or is paradise one day closer ?

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Might check with someone who repairs musical instruments like tubas an trumpets.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

What is the requirement for flow surface profile accuracy of the duct? You can pull a .2" dent out of a 3" OD x .035 wall 625 Inconel tube using a slide hammer and some wires welded to the outer wall. But the result will not be perfect. There will also be some local work hardening of the 625 Inconel material.

The best way to make a clean repair might be to cut out the damaged tube section and butt weld in a patch.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

I agree that a brass instrument repairman might be able to help. He won't like working with Inconel at all; tell him it fights back way harder than brass.

I have found that an ordinary grease gun can apply hydraulic pressure well enough to 'overdo' it easily. If you can localize the pressurized area with temporary bulkheads, maybe.

I'm concerned about the localized high curvature areas; maybe with steady internal pressure, an auto body guy could hammer around them and bump out most of the depth, but probably not the actual crease.

Now I'm thinking you have a chance if you hire a brass repairman and an old auto body guy to work together, and go over the pipes dent by dent.


Mike Halloran
Pembroke Pines, FL, USA

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

When I worked at Convair in San Diego in the 90s we had a series of balls,(Pull through ball mandrels) each one a couple of thousandths bigger than the next mounted on a 1/2" diameter cable. these were lubricated and drawn through a duct to burnish out minor defects. Most of that stuff ended up on the junk pile when Convair shut up shop in SD, But if you can afford to spend 30 K , you can make new ones.
The bigger question is can you de-mount the ducts and get them into a shop. Panel beating will also work ,if you can find people with the hand skills. While a panel wheeling machine may be out of the question, a pneumatic planishing hammer on a specialized yoke may be able to get at some damaged areas. Al lot here is going to depend on the twists and turns of the duct. One question, how were the originals made? were they bent from tube, Drop hammered in two halves and welded together or hydroformed ?
B.E.

You are judged not by what you know, but by what you can do.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

wktaylor-

A while back I briefly worked for a company that specialized in manufacturing ducts and fluid pipes for aerospace applications. The cryogenic propellant pipes they made for launch vehicles were 718 Inconel with mostly butt welds. The butt welds on the flow surfaces were often smoothed using roller planishing. They had all sorts of specialized tooling for the roller planishing equipment that would allow them to access welds inside of tube bends. So as berkshire noted this might be a suitable method to repair minor damage in your duct walls.

I believe the company had an MRO group, so you might give them a call. The folks on the manufacturing side I met there all seemed to be very nice and willing to help, and I'm sure someone there would be happy to spend a few minutes on the phone discussing your repair. Even if they are not in a position to do the work themselves, they might be able to recommend someone that can.

Good luck to you.
Terry

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

QUESTION: Does this duct see internal pressure, and if yes, what pressure?

COMMENT: Any sharp edges remaining no matter what method is used to burnish the defects will of course be stress risers and any heating will affect strength integrity.

RECOMMENDATION: Contact AZUSA Pipe and Tube Bending in Azusa, California (Chris). They are extremely adept at this kind of condition.

Bellows Manufacturing and Research, Inc.
https://bellowsmfg.com

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Talk to an auto body repair company. I heard that some of their equipment uses a vacuum. Others use heat to soften the material in combination to the vacuum.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

(OP)
All... further research...

I have heard of pulling re-sizing-balls, heavily lubricated, thru the dent: each ball ~0.002--0.004 larger than the last. Moderate success with ductile tubing and no joints. Music instrument folks dealing with brass instruments seem to use this reliably.

My Inconel 625 pneumatic duct assys have any where from 2-to-4 bellows per assy. Sizing balls would be a tight fitt with these bellows; so can't take the chance. Might be practical to cut sections apart so that the balls do not pass thru the bellows; then re-weld the sections together. What a pain.. but probably do-able.

A tubing-repair shop chief just informed me that they have an 'old, homemade, hydraulic expansion tool' made specifically for this purpose. An expansion tool-head is made for each OD tubing; and assumes minimal difference in ID between fairly thin wall thicknesses for each OD ["one size fits all ODs regardless of wall thickness"]. The barrel shaped expansion head is sliced in-half axially and has a hydraulic piston [bladder?] that forces the 1/2s open. The tool-head is connected with a long braided hose to a hydraulic hand pump for opening/relieving, which also defines/holds angular position of the head [hose is torque/twist resistant; and a marking stripe on the hose side gives some visual reference with a stripe along the side wall]. Tool-head inserts to the back side of the dent, positioned so that the expansion will occur directly against the dent [and opposite side-wall]; then it is expanded-closed, expanded-closed, etc... in short increments thru the dent-area. The shop chief believes it will fit thru our bellows without conflict. Total tool-head movement from fully collapsed to fully open is ~0.20" [=max dent limit by default?] for the 3.0-OD tubing we have. NOTE: ; and which has a pressure relief valve to allow it to relax after expanding. Apparently they've had "good success' on CRES Inconel and aluminum tubing. Biggest issue is "watching the dent carefully" so that when it has been pressed-out to round contour, then "STOP"... otherwise it might bulge-out the tubing wall [lesson learned??].

We will have a demo in a few days on a mildly damage tubing assy. If this works, could solve many problems and really keep repair costs down.

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????


It sounds like you have the job covered Will , You can also buy hydraulic tube expanders that open like the segments of an orange.
B.E.

You are judged not by what you know, but by what you can do.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

wktaylor-

If these ducts do not need to be repaired at an approved facility your best bet might be to send them to a fabricator that builds race engine exhaust systems. F1, Indy and LeMans race engines all use Inconel exhaust systems. These exhaust systems are hand fabricated from butt-welded tube bends with wall thickness close to .020". One of these race exhaust fabricators could cut out the damaged wall section, butt-weld in a fitted patch, and even weld a doubler over the patch if necessary. It's the off-season for racing, so if you're quick you can probably get them to do the work fast and fairly cheaply.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Will any heat treatment be necessary after the rework?
What about NDI? I haven't worked with Inconel before so I'm just curious.

Too bad the brits didn't have you around ten years ago, Wil, you could have saved a few of their Nimrods with your attention to detail.

STF

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

SparWeb-

If the tube wall dent was deep and had a "sharp radius crease", then there was likely significant yielding of the material. If you use a hydraulic inner/outer die forming process to "flatten" the dent, the result will probably look like a series of squashed wrinkles in the tube wall.

Just like removing a deep dent in a steel auto fender, the stretched metal in the dent must be "shrunk" to make the repair look smooth. The metal shrinking process used on steel auto body panels is usually done by carefully heating and quenching the area around the dent, working from the outer edge of the dent inward. There are also some mechanical surface working techniques like hammer peening that can shrink sheet metal parts.

Since 625 Inconel tends to work harden, some heat treat/stress relief may be required. As for NDI, a surface etch and dye pen would work for surfaces that are accessible. But if both the inner and outer surfaces are not accessible, some other type of NDI such as ultrasound would be required. And if you wanted to be extra safe you could perform an acceptance level pressure test on the repaired duct.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

do you have a picture of it maybe you can share?

Bellows Manufacturing and Research, Inc.
https://bellowsmfg.com

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

(OP)
Berkshire...
"...You can also buy hydraulic tube expanders that open like the segments of an orange". >>> Do You know what companies sell these tools?

tbuelna...
We have considered cutting out damage tubing segments if dents remain sharp centered/edged/creased. As stated sharp creases/dents are stress risers. Small lumps/bumps ~= wall thickness, W/O sharp features will be acceptable.

SparWeb...
Visual/dimensional inspections.
NDI
Penetrant inspect for cracks, chips, etc.
Ultrasonic inspect wall for eratic thickness variations [IE: sudden thinning, ludders-thinning, etc]
Proof pressure test [restrained bellows]

Abrasive blast or etch repair-disposition # adjacent to existing part markings.

http://files.engineering.com/getfile.aspx?folder=8...

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Wil,

I think Berkshire was thinking of this type, common around muffler shops and suitable for very light (<.05 wall mild steel) gauge large dia. tubing:

http://www.amazon.com/Exhaust-Tail-Pipe-Expander/d...

Driving that type with the nut/bolt arrangement they typically come with limits the amount of internal pressure that can be generated due to the torque/tensile limits of the bolt and driver. Getting the darn things started can also be a pain, especially on new, smooth or oily tube surfaces. If you can find version

Expanders capable of heavier wall expansion/flaring are typically meant for heat exchanger tubesheet joints, and aren't made to slide very far into a tube. Like these:

http://www.amazon.com/Exhaust-Tail-Pipe-Expander/d...

It sounds like what you want is something like the first one, but with an attached very small and compact hydraulic cylinder providing the pull/expand function, and the entire thing capable of being snaked down a long, twisty piece of tubing with a hydraulic line attached...I've never seen one, but am waiting and reading this thread in anticipation of being surprised. Maybe I will design one over the holidays and sell you the prototype.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

aaaand...shortly after hitting "post" I recalled one other technique I have seen used, with mixed results.

If the material has ductility at low temperatures, you can use the expansion of freezing ice (or some other liquids, I think bismuth and other low mp alloys also expand on freezing - I know plutonium does, but that might not be practical for you) to pop small dents, even repeatedly freezing/thawing to slowly "ratchet" the dent out. In your case, you would want to rig some expansion plugs into the pipe to trap the water/liquid where you want it, then dip the thing into liquid nitrogen, or roll it into a deep freeze.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Ok,
The unit I saw was actually a conversion that used the screw type expander and replaced it with a Greenlee type hydraulic pulling cylinder.
They say it is capable of expanding 12 gauge mild steel fence posts. This can start as the basis for a custom head to get into a tube and reform it by gently stretch forming the tube.
B.E.

You are judged not by what you know, but by what you can do.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

The cylinder in the picture shown by Berkshire has a side port, and the cylinder itself is larger in diameter than the expander...so getting it into wk's tube might not work. But otherwise, yes, that's the right approach. Ideally, the joint between the cylinder and expander body would also have a pin joint, allowing the assembly a bit more flexibility to fit through a pipe bend.

The next problem to solve is what do you do about non-circular section ducts...

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

(OP)
btb...

The expander head(s) the local tube shop made have the ratio/appearance of itty-bitty "beer kegs", IE: noticibly convex barrel '(_)' shape, length ~= unexpanded barrel diameter. The hydraulic hose port is in the flat base of the 'keg' [axis]. The stubby convex barrel shape allows the expander head to pass thru fairly tight elbows. OH yeah: the Expander head is made of steel; the techs places a powerful permanent magnet on the OD to locate the center of the barrel in the duct for relatively precise positioning [obviously works for non-magnetic tubing alloys only]. during expansion the mech keeps his eyes/hand on the dent site to 'see/feel' how the process is going.

The various tube expanders mentioned by others, all appear to be intended for end-of-tube-expansion use only.

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Trueblood,
There are other cylinders that can be used on a Portapower type hand pump, including some that have end fittings to get down inside a tube.
I have some alligator jaw type body jack fittings that could also be modified to spread a pipe by fitting curved ends, that could be used on non circular sections.
This is precisely what Wills crew is doing. It sounds like right now, that Wills crew has a handle on the problem, and that they need to fabricate more custom machines for the parts they cannot handle yet.
B.E.

You are judged not by what you know, but by what you can do.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

(OP)
berkshire... I think You are right.

The shop techs who've been around awhile are worth their weights in gold. They can/have come up with some amazing 1-off tools for solving problems like this.

DANG. Too bad we [engineers] weren't clued in earlier to prevent scrapping some ducts that probably could have been salvaged.

Off-topic note.
During my general research on CRES and HRA duct failures/repairs I ran across a report that catagorized high temp duct primary-causes for failure. Crazy... I have seen each of these 'failure modes' in my career as a field service engineer.

1. Non-spec welds/weld-beads. IE: too big, too small, erattic width, re-entrant, undercutting, poor penetration, dirty/contaminated welds due to poor pre-cleaning practices and/or moisture, and/or inadequate inert gas coverage, etc.

2. Duct manufacturing [alignment] errors that lead to poor "natural fit". IE: built-in misalignment that causes mechanics to force [pre-stress] these sections to fit. In some cases this means over-stressing no-aligned flanges and-or severe movements of flexible joints [bellows, etc] to make it fit.

3. Inadequate flexibility and/or restraint design practices. IE: too stiff and/or too flexible for internal pressure, thermal, inertia [mass-flow] loads/strains; and/or mating structure flexure/strain.

4. Maintenance abuse. Mishandling before installation, mishandling during installation/removal; poor storage practices; inadvertant use as hand-hold ['chinning bar'], etc when installed; or impact/contact during other maintenance [dropped tools or trapped FOD, etc]; or failure to follow established tech data to the letter.

NOTE.
In one case, the tech data had very specific sequences to follow in order to to remove, then re-install or replace, certain duct sections. The mechs were struggling to replace one of the sections that was found cracked. The mechs had removed it, and were trying to install the replacement, without even taking a look at the tech data/procedures. Restarting the process 'by-the-book', with some variations due to the disassy circumstances, finally allowed the section to fit 'adequately'.

5. Unanticipated operating environment; or operating environment that becomes more severe over time; or a system failure up/down stream that leads to unanticipated consequences.

NOTE.
The acft I work on have all been re-engined. The new engines supply bleed air at roughly the same pressure/temperature/flow... but are able to supply this bleed air continuously; as opposed to discontinuously... due to much higher re-engine thrust ratings.

NOTE. In one acft I worked on, a duct system failure down stream caused a dramatic rise in temperature [350F up-to 650F] up-stream of the break, since the bleed-air was passing thru the up-stream pre-coolers way-too-fast and couldn't reduce the temperature as designed. This extremely hot air did very bad things to wire harnesses and aluminum structure.

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????


https://www.youtube.com/watch?v=cSHD9tI2vWM
I can attest this method works pretty slick on dented and even creased dirt bike exhaust ( < .06 inch thick mild steel rolled cones and "pipe" ).

In addition I prefer to have a method to modulate (release, mostly) the pressure as well. I think it helps me avoid bulges way better than just pulling the torch away.

I have no clue about the metallurgical effects of heating your material to the point its yield strength is lowered.
Legend holds, and my experience confirms, that a mild steel pipe repaired this way will dent somewhat easier the next time it and the rock meet.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Wktaylor,
it occurs to me that while you are wrestling with damaged ducts, your bellows may be suffering the same fate.
Here is a company that manufactures bellows and expansion joints, that you may be able to work with. Whether or not they will do Milspec work you will have to find out.

You are judged not by what you know, but by what you can do.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

Good point about the metal bellows berkshire. Most people think that since metal bellows are designed to flex they are immune to being over-stressed. Often metal bellows are only designed to handle stresses produced from a very limited amount of compression/tension, bending and torsion. The duct company I worked at designed and manufactured their own metal bellows. They were very highly engineered devices and were not simple to manufacture. For example, the convoluted bellows itself was constructed from multiple thin layers of metal rather than a single layer. Many aircraft bellows, like those that might be used on wktaylor's high temp/pressure bleed air ducts, might exceed stress limits if they are displaced just a modest amount beyond what they are designed for. The bellows wall must be thin enough to flex without applying too much force, but must also be thick enough to handle the duct pressure without bursting or ballooning.

I recall that the bellows were constrained in a fixture during welding that preloaded it and aligned the ends. If there is a need to cut a full section out of the duct and weld in a new piece, the people doing the repair will need to make sure the duct is fixtured accurately.

RE: Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss????

whilst restoring the shape is a good thing, what about the strength properties ?

another day in paradise, or is paradise one day closer ?

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