Pietenpol-List: Re: exhaust manifold

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Pietenpol-List: Re: exhaust manifold

Post by matronics »

Original Posted By: Wayne Bressler
Many years ago on another homebuilt, I had a stainless system built. It had slip joints and ball joints where appropriate to allow for expansion. The various pictures I've seen of the current batch of Pietenpol exhaust systems don't have those; maybe they should.It lasted past when I sold it, don't know how it fared after that, and I sold it early on.David Paule________________________________________________________________________________
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Re: Pietenpol-List: Re: exhaust manifold

Post by matronics »

Original Posted By: "Jack"
I was starting to wonder if any of these failures were due to poor exhaust system design. Tony Bingelis makes it very clear that any system, regardless of material or welding technique, will fail if it is not allowed to flex/expand/contract relatively unimpeded.As David said, the use of ball joints, slip joints, etc would help to ensure a long exhaust live.I don't know if this was the problem with anybody here's exhaust. I'm just sharing some info from the Bingelis books.Wayne Bressler Jr.Taildraggers, Inc.taildraggersinc.com________________________________________________________________________________
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RE: exhaust manifold [was Re: Pietenpol-List: humped center section]

Post by matronics »

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Jack, great post, thanks! Just purchased a tig and have been reading up onit. I thought to myself, why mess with "back filling with argon", well nowI know. Here is a fantastic site for welding tips,http://www.weldingtipsandtricks.com/index.html and some info on shieldingthe backside (not CYA-cover your ass). One article..."One thing I have to mention about welding stainless steel is that the backside of the weld needs argon shielding just as much as the front. The photoof the aircraft engine stator being prepared for welding displays specialtooling made for the purpose of shielding the back side of the weld. If thepenetration side is not shielded with argon, it will "sugar" which is aslang word for oxidize. Granulation is another descriptive term thataccurately describes what happens. A close-up photo of the granulated orsugared stainless steel weld reveals why sugared welds fail in service.There are deep pits and crevices that are bound to develop into cracks".They also have information on "how to" construct "back shield" devices.Thanks again!JackDSMFor those contemplating stainless steel ehaust systems, let me share alittle pearl of wisdom that I learned just a bit too late:My original exhaust system on my Pietenpol was TIG welded stainless steel,welded by my neighbor (who also welded my aluminum fuel tank). The weldslooked good, but after about 30 hours of operation, the left stack broke offand was only kept from departing the airplane by the SCAT hose on the heatmuff. I had my neighbor re-weld it, with an additional strut to helpdistribute the load. Then I flew the airplane to Brodhead and OSH (this wasin 2005). On the way home, the right side stack broke off and was againheld in place by the SCAT hose. I had to find a local welder make emergencyrepairs so I could make it home.I decided that stainless was simply not a good choice and made a whole newset from plain carbon steel, which I could weld myself. No problem with it,except that it has begun to rust. In another 10 years or so I'll have toreplace it.Meanwhile, I was talking to a fellow who makes exhaust systems for race cars(TIG welded stainless), telling him of my troubles. He asked "What did youdo to shield the inside of the tubing?"I just looked at him with a stupid look on my face (fairly easy for me todo), and said "Huh?"He said, "TIG shields the area around the weld with argon gas to prevent theweld from burning, but with such thin walled material, the metal on theinside of the tube is just as hot as the outside. You've got to shield itas well."He said that when he does a job like this, he plugs one end of the tube,then turns on the gas from the TIG torch and uses it to flood the entiretube with Argon. He tests to see if he has enough by striking a match andinserting it into the tube. If it doesn't go out immediately, he knows hedoesn't have enough Argon to shield the weld.So when it comes time to replace my exhaust system again, I may givestainless another try, using this technique.Jack PhillipsNX899JPRaleigh, NC-----Original Message-----
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Re: Pietenpol-List: Re: exhaust manifold

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Original Posted By: helspersew(at)aol.com
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Re: Pietenpol-List: Re: exhaust manifold

Post by matronics »

Original Posted By: helspersew(at)aol.com
I've also heard you don't have to worry about preheating thin material=2C but some of the more knowledgable people in the business say yes to preheating. FAA still recommends gas welding=2C but some production aircraft are MIG welded. Go figure.Doug DeverIn beautiful Stow OhioSubject: Re: Pietenpol-List: Re: exhaust manifoldDate: Tue=2C 27 Oct 2009 20:28:33 -0400
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Re: Pietenpol-List: Re: exhaust manifold

Post by matronics »

Original Posted By: Lloyd Smith
The plating causes something called hydrogen embrittlement. Wikipedia has a good article and explains it better than I can:http://en.wikipedia.org/wiki/Hydrogen_embrittlementThe strength of 1,000 MPa that the article mentions as a threshold for concern is 145,000 psi, considerably stronger than the ductile materials used in exhaust systems, so probably there's not going to be an issue. 4130, normalized, is about 90,000 psi and lower at the welds. There's lots of margin there.Although baking the parts after plating is the general solution to the problem, according to the article it needs to be done relatively soon after plating. So although we'd expect that the exhaust system is going to get plenty hot enough in service, it won't happen soon enough.It's worth mentioning that that often chrome plating companies don't first plate with copper and then with nickel as the aerospace spec says to do. They just plate directly with the chrome. Chrome doesn't stick that well to steel if there's any flexing, since they have different coefficients of thermal expansion and different modulus of elasticity (no, I don't remember the chrome values off-hand, sorry). But we've all seen plenty of motorcycle exhausts that were plated, successfully, so don't worry about it. Odds are it'll be fine. Just something to check at annual, and you'd do that anyway.David Paule I TIG welded my 4130 exhaust stacks on the model A, and afterward had them chrome-plated. I was informed that this was not a good idea, because they would be prone to cracking for some reason I can't remember. Can anyone knowledgeable fill me in on this? Thanks. Dan Helsper Poplar Grove, IL. ________________________________________________________________________________Date: Tue, 27 Oct 2009 21:28:11 -0400Subject: Re: Pietenpol-List: Re: exhaust manifold
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Re: exhaust manifold [was Re: Pietenpol-List: humped center section]

Post by matronics »

Original Posted By: Ryan Mueller
Subject: Re: exhaust manifold [was Re: Pietenpol-List: humped center section]
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> RE: exhaust manifold [was Re: Pietenpol-List: humped center

Post by matronics »

Original Posted By:> ** owner-pietenpol-list-server(at)matronics.com [mailto:
>> Actually, the repair on the way back from OSH was made by a professional> welder, TIG welded. It lasted nearly twice as long as the first one (50> hours). It cracked too. At the weld.>>> You=92ve confused me a bit ' in your 5th sentence you said =93you can weld> 4130 without preheating or fear of cracking.=94 Then 3 sentences later you> say =93With 4130 the area will need to be preheated to prevent cracking=94.> Which is it?>>> Anyway, to some extent I agree with you ' I like oxyacetylene welding.> However, for some applications TIG is far better. I=92ve tried gas welding> aluminum, I=92ll leave that for the pros. I also tried gas welding stainless> and burned up a lot of test material without any good welds. MIG I have no> experience with, but I know Champion Aircraft uses MIG to build Citabrias> and Decathlons (at least the Citabria I helped rebuild had a lot of little> twigs of welding rod stuck to it like MIG tends to leave behind).>>> This was just a tip given o me that I passed along. I have not tried it,> but it makes sense to me. Your mileage may vary.>>> Jack Phillips>> NX899JP>> Raleigh, NC>>> ------------------------------>
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> > RE: exhaust manifold [was Re: Pietenpol-List: humped center

Post by matronics »

Original Posted By:> > owner-pietenpol-list-server(at)matronics.com
> >> pietflyr(at)bellsouth.net>>> >> > For those contemplating stainless steel ehaust systems, let me share a> > little pearl of wisdom that I learned just a bit too late:> >> > My original exhaust system on my Pietenpol was TIG welded stainless> steel,> > welded by my neighbor (who also welded my aluminum fuel tank). The welds> > looked good, but after about 30 hours of operation, the left stack broke> off> > and was only kept from departing the airplane by the SCAT hose on the> heat> > muff. I had my neighbor re-weld it, with an additional strut to help> > distribute the load. Then I flew the airplane to Brodhead and OSH (this> was> > in 2005). On the way home, the right side stack broke off and was again> > held in place by the SCAT hose. I had to find a local welder make> emergency> > repairs so I could make it home.> >> > I decided that stainless was simply not a good choice and made a whole> new> > set from plain carbon steel, which I could weld myself. No problem with> it,> > except that it has begun to rust. In another 10 years or so I'll have to> > replace it.> >> > Meanwhile, I was talking to a fellow who makes exhaust systems for race> cars> > (TIG welded stainless), telling him of my troubles. He asked "What did> you> > do to shield the inside of the tubing?"> >> > I just looked at him with a stupid look on my face (fairly easy for me to> > do), and said "Huh?"> >> > He said, "TIG shields the area around the weld with argon gas to prevent> the> > weld from burning, but with such thin walled material, the metal on the> > inside of the tube is just as hot as the outside. You've got to shield it> > as well."> >> > He said that when he does a job like this, he plugs one end of the tube,> > then turns on the gas from the TIG torch and uses it to flood the entire> > tube with Argon. He tests to see if he has enough by striking a match and> > inserting it into the tube. If it doesn't go out immediately, he knows he> > doesn't have enough Argon to shield the weld.> >> > So when it comes time to replace my exhaust system again, I may give> > stainless another try, using this technique.> >> > Jack Phillips> > NX899JP> > Raleigh, NC> >> > -----Original Message-----
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