Aircraft Pneumatic Duct Wall severely dented/creased: methods/techniques to restore roundnesss???? 1

[WKTaylor]

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.

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

 

[rb1957]

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 ?

 

[KENAT]

Hmm, sounds likd conventional English Wheel is out of the question.

http://www.aviationpros.com/article...ight-into-using-this-sheet-metal-forming-tool

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[3DDave]

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

 

[KENAT]

How about a museum or similar that restore vintage A/C?

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[tbuelna]

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.

 

[MikeHalloran]

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

 

[berkshire]

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.

 

[tbuelna]

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

 

[bellowsmfg]

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

 

[Dougt115]

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.

 

[WKTaylor]

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"

 

[berkshire]

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.

 

[tbuelna]

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.

 

[Sparweb]

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

 

[tbuelna]

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.

 

[bellowsmfg]

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

Bellows Manufacturing and Research, Inc.

https://bellowsmfg.com

 

[berkshire]

There is a company named Eckold that makes rubber bonded shrinking and stretching hammers for specialized work.
B.E.

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

 

[WKTaylor]

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/getfil...nch_Dia_X_035-inch_WT~Typ_Damage_at_Elbow.jpg

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"

 

[btrueblood]

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/dp/B001Z0RF1G

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/dp/B001Z0RF1G

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.