Pilots of America Message Board

Home Live Chat
Go Back   Pilots of America Message Board > Controlled Airspace > Maintenance Bay

Maintenance Bay Looking for a good mechanic? Got a question about changing a landing light or installing a new radio? Any mechanical questions you've got, someone here probably has an answer for you!

Reply
 
Thread Tools Display Modes
Old May 3rd, 2012, 03:46 PM
Posted in reply to Skylane81E's post "Re: Corrosion.."
  #76
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by Skylane81E View Post
I think the real question is what regulatory leg would I have to stand on to tell him that it is unairworthy?
very easy..

" your aircraft is not considered safe for flight "

you the pilot have now been informed, you can't comply with 91.7

Last edited by Tom-D; May 3rd, 2012 at 03:48 PM.
Tom-D is offline   Reply With Quote
Old May 3rd, 2012, 04:01 PM
Posted in reply to N801BH's post "Re: Corrosion.."
  #77
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by N801BH View Post
In reality, sheet metals, whether it be steel, aluminum or other materials is actually a forging to some extent.. Rolling metals using high pressure is a form of forging it... With a real high powered microscope you can see the granular structure of tin foil..
This is true, but only the ZINK alloys are plagued with intergrainular corrosion due the low melting point of ZINK.
Tom-D is offline   Reply With Quote
Old May 3rd, 2012, 04:27 PM
Posted in reply to N801BH's post "Re: Corrosion.."
  #78
iHenning Henning is offline
(User ID: Henning)
Taxi to Parking
 
Henning's Avatar
 
Join Date: Feb 2005
Location: Ft Lauderdale FL
Posts: 42,589
Re: Corrosion..

Quote:
Originally Posted by N801BH View Post
In reality, sheet metals, whether it be steel, aluminum or other materials is actually a forging to some extent.. Rolling metals using high pressure is a form of forging it... With a real high powered microscope you can see the granular structure of tin foil..

Yeah, kinda, rolling mills and extrusion use pressure, but it is not near the pressure that the forgings of aerospace are made from using these machines:http://boingboing.net/2012/02/13/machines.html

__________________
Quote:
There is enough for everyone; there is never enough for the greedy.-Mahatma Gandhi

All life is precious, the problem is there is just too much of it.-Dali Lama
Henning is offline   Reply With Quote
Old May 4th, 2012, 02:04 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #79
Doug DouglasBader is offline
(User ID: DouglasBader)
Line Up and Wait
 
Join Date: Apr 2012
Posts: 896
Re: Corrosion..

Quote:
Neither of those two aircraft are made from .032" 2024-t3 sheet.

Intergranular corrosion does occur, but only in thicker forgings and always starts from with in the grain boundaries never on the surface.
That's the basic characteristic of intergranular corrosion, although I've seen it occur in some fairly thin parts, generally in 7075. What appears initially to be filiform corrosion under a coating quickly becomes something else, as one begins to remove material. I've found it on a number of panels on Sabreliners.
DouglasBader is offline   Reply With Quote
Old May 4th, 2012, 02:43 AM
Posted in reply to DouglasBader's post "Re: Corrosion.."
  #80
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by DouglasBader View Post
That's the basic characteristic of intergranular corrosion, although I've seen it occur in some fairly thin parts, generally in 7075. What appears initially to be filiform corrosion under a coating quickly becomes something else, as one begins to remove material. I've found it on a number of panels on Sabreliners.
Yes, that's usually filiform corrosion or direct chemical attack, it is caused by microbe's pizz or electrolyte attacking the alclad, and will quickly get between the alclad and the basic alloy, causing the alclad to exfoliate, But it is not considered intergrainular, that actually starts between the grain boundaries.

Each of the types of corrosion is named by its cause.

read AC 43,13 chapter 6

Last edited by Tom-D; May 4th, 2012 at 02:46 AM.
Tom-D is offline   Reply With Quote
Old May 4th, 2012, 07:12 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #81
Doug DouglasBader is offline
(User ID: DouglasBader)
Line Up and Wait
 
Join Date: Apr 2012
Posts: 896
Re: Corrosion..

Tom,

I understand corrosion very well, being a long time career mechanic and inspector, as well as former director of maintenance (several times).

Intergranular is internal to the metal, but is often found having surfaced, and may appear to be minor surface corrosion. Sometimes it's like chasing a gopher hole; a small amount on the surface becomes veins or areas beneath the surface, and an attempt to remove corrosion quickly leads to discovery of a very unairworthy panel or part.
DouglasBader is offline   Reply With Quote
Old May 4th, 2012, 11:32 AM
Posted in reply to DouglasBader's post "Re: Corrosion.."
  #82
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by DouglasBader View Post
Tom,

I understand corrosion very well, being a long time career mechanic and inspector, as well as former director of maintenance (several times).

Intergranular is internal to the metal, but is often found having surfaced, and may appear to be minor surface corrosion. Sometimes it's like chasing a gopher hole; a small amount on the surface becomes veins or areas beneath the surface, and an attempt to remove corrosion quickly leads to discovery of a very unairworthy panel or part.
What you say it true, but the difference between intergrainular and any other is where it starts. Only intergrainular starts internally and breaks out to the surface. all other types of corrosion starts on the surface and eats away the metal and may cause the alclad to exfoliate. That doesn't mean it is intergrainular.

Last edited by Tom-D; May 4th, 2012 at 11:35 AM.
Tom-D is offline   Reply With Quote
Old May 4th, 2012, 04:01 PM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #83
Rotor&Wing RotorAndWing is offline
(User ID: RotorAndWing)
Final Approach
 
RotorAndWing's Avatar
 
Join Date: Sep 2008
Location: Other side of the world
Posts: 6,503
Re: Corrosion..

Quote:
Originally Posted by Tom-D View Post

My 48 170 had the entire rear cabin former replace, along with 22 other fuselage skins, including the whole horizontal stab, rudder and elevators skins, due to the aircraft being comprised of 4 other aircraft made into one and ending up bent 3/4" out of alignment, and the wrong elevator installed. 6 months of work. estimated 30,000 in labor and materials.
I thought N2801C was a 1954 Model? Also, are you sure you actually replaced any formers or fuselage skins?
__________________


"Carelessness and overconfidence are more dangerous than deliberately accepted risk."---------------Wilbur Wright 1901


RotorAndWing is offline   Reply With Quote
Old May 4th, 2012, 07:57 PM
Posted in reply to RotorAndWing's post "Re: Corrosion.."
  #84
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by Rotor&Wing View Post
I thought N2801C was a 1954 Model? Also, are you sure you actually replaced any formers or fuselage skins?
how many 170s have I owned?

Proving once again you make conclusions based upon what you think you read. not what was actually said.

If you really were a FAA employee you could look that info up.

Last edited by Tom-D; May 4th, 2012 at 08:00 PM.
Tom-D is offline   Reply With Quote
Old May 4th, 2012, 08:12 PM
Posted in reply to Tom-D's post "Corrosion.."
  #85
Bruce T. kontiki is offline
(User ID: kontiki)
Line Up and Wait
 
kontiki's Avatar
 
Join Date: May 2011
Posts: 782
Re: Corrosion..

Photo 3 looks like it's it's got a hole corroded all the way through!
__________________

In theory, there is no difference between theory and practice however, experience suggests that in practice, there is!

My posts reflect my personal views and are not in any way endorsed or approved any organization I'm affiliated with.
kontiki is offline   Reply With Quote
Old May 4th, 2012, 08:14 PM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #86
Rotor&Wing RotorAndWing is offline
(User ID: RotorAndWing)
Final Approach
 
RotorAndWing's Avatar
 
Join Date: Sep 2008
Location: Other side of the world
Posts: 6,503
Re: Corrosion..

Quote:
Originally Posted by Tom-D View Post
how many 170s have I owned?

.
You owned 2623V (1948) and 2801C (1954).
__________________


"Carelessness and overconfidence are more dangerous than deliberately accepted risk."---------------Wilbur Wright 1901


RotorAndWing is offline   Reply With Quote
Old May 4th, 2012, 09:13 PM
Posted in reply to RotorAndWing's post "Re: Corrosion.."
  #87
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by Rotor&Wing View Post
You owned 2623V (1948) and 2801C (1954).
And..

I have mentioned both of them here, but not the others.

Feeble at best.

Last edited by Tom-D; May 4th, 2012 at 09:15 PM.
Tom-D is offline   Reply With Quote
Old May 4th, 2012, 09:19 PM
Posted in reply to kontiki's post "Re: Corrosion.."
  #88
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by kontiki View Post
Photo 3 looks like it's it's got a hole corroded all the way through!
We will know in the next couple days, he says he has it nearly cleaned up.
Tom-D is offline   Reply With Quote
Old May 5th, 2012, 12:51 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #89
Doug DouglasBader is offline
(User ID: DouglasBader)
Line Up and Wait
 
Join Date: Apr 2012
Posts: 896
Re: Corrosion..

Quote:
What you say it true, but the difference between intergrainular and any other is where it starts. Only intergrainular starts internally and breaks out to the surface. all other types of corrosion starts on the surface and eats away the metal and may cause the alclad to exfoliate. That doesn't mean it is intergrainular.
No, it means it's intergranualar when you begin treating the surface, remove material and discover that the entire piece is infected with intergranular corrosion, which is often how it's found.
DouglasBader is offline   Reply With Quote
Old May 5th, 2012, 01:12 AM
Posted in reply to DouglasBader's post "Re: Corrosion.."
  #90
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by DouglasBader View Post
No, it means it's intergranualar when you begin treating the surface, remove material and discover that the entire piece is infected with intergranular corrosion, which is often how it's found.
That's not what it says in the AC 43,13 :


6-17. INTERGRANULAR CORROSION.
Inter-granular corrosion is an attack on the grain boundaries of a metal. A highly magni- fied cross section of any commercial alloy shows the granular structure of the metal. It consists of quantities of individual grains, and each of these tiny grains has a clearly defined boundary which chemically differs from the metal within the grain. The grain boundary and the grain center can react with each other as anode and cathode when in contact with an electrolyte.
(See figure 6-9.)
Rapid selective corrosion of the grain boundaries can occur. High-strength aluminum alloys such as 2014 and 7075 are more susceptible to inter-granular corrosion if they have been improperly heat-treated and then exposed to a corrosive environment.

6-18. EXFOLIATION CORROSION. Ex- foliation corrosion is an advanced form of in- ter-granular corrosion and shows itself by lift- ing up the surface grains of a metal by the force of expanding corrosion products occur- ring at the grain boundaries just below the sur- face. (See figure 6-10.) It is visible evidence of inter-granular corrosion and is most often seen on extruded sections where grain thick- ness are usually less than in rolled forms.It is visible evidence of inter-granular corrosion and is most often seen on extruded sections where grain thickness are usually less than in rolled forms.

Last edited by Tom-D; May 5th, 2012 at 01:20 AM.
Tom-D is offline   Reply With Quote
Old May 5th, 2012, 01:18 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #91
Doug DouglasBader is offline
(User ID: DouglasBader)
Line Up and Wait
 
Join Date: Apr 2012
Posts: 896
Re: Corrosion..

No one is arguing that, Tom.

Often it goes undiscovered until it surfaces, unless the part, panel, or component is subject to an inspection procedure that might otherwise identify that corrosion.

Not uncommonly, intergranular goes undiscovered until it surfaces somewhere. By then, it's far too late.
DouglasBader is offline   Reply With Quote
Old May 5th, 2012, 01:27 AM
Posted in reply to DouglasBader's post "Re: Corrosion.."
  #92
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by DouglasBader View Post
No one is arguing that, Tom.
The argument was "what is Intergrainular corrosion."

I hope every one now knows it starts from with in the metal, it is the only type that does.
Tom-D is offline   Reply With Quote
Old May 5th, 2012, 01:37 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #93
Doug DouglasBader is offline
(User ID: DouglasBader)
Line Up and Wait
 
Join Date: Apr 2012
Posts: 896
Re: Corrosion..

There was no argument, Tom. I never disagreed with that. I think we're all familiar with the concept of intergranular corrosion.

What some may not be familiar with is what it does, how it is and isn't detected, and where it can be found.
DouglasBader is offline   Reply With Quote
Old May 5th, 2012, 02:20 AM
Posted in reply to DouglasBader's post "Re: Corrosion.."
  #94
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

Quote:
Originally Posted by DouglasBader View Post
There was no argument, Tom. I never disagreed with that. I think we're all familiar with the concept of intergranular corrosion.

What some may not be familiar with is what it does, how it is and isn't detected, and where it can be found.
the AC 43,13 pretty much tells it all.

Intergranular is seldom found in the Cessna and pipers, Direct chemical attack and filliform yeah they all have it.

I don't believe we fully understand what each other writes.
Tom-D is offline   Reply With Quote
Old May 5th, 2012, 03:12 AM
Posted in reply to Tom-D's post "Corrosion.."
  #95
Bruce T. kontiki is offline
(User ID: kontiki)
Line Up and Wait
 
kontiki's Avatar
 
Join Date: May 2011
Posts: 782
Re: Corrosion..

Assuming is something common and easy to work with (like 2024-T3), you could drill it off. Make a forming block out of wood, get some dead soft stock and form a replacement. Heat treating it might be an issue, I don't know where I'd look for a heat treat oven on a GA field. Given it's a Cessna it's probably not real thick sheet Metal. It would come out of the oven a little twisted, but usually you can pull it into place when you shoot it back in.
__________________

In theory, there is no difference between theory and practice however, experience suggests that in practice, there is!

My posts reflect my personal views and are not in any way endorsed or approved any organization I'm affiliated with.
kontiki is offline   Reply With Quote
Old May 5th, 2012, 03:52 AM
Posted in reply to Tom-D's post "Re: Corrosion.."
  #96
iHenning Henning is offline
(User ID: Henning)
Taxi to Parking
 
Henning's Avatar
 
Join Date: Feb 2005
Location: Ft Lauderdale FL
Posts: 42,589
Re: Corrosion..

Quote:
Originally Posted by Tom-D View Post
That's not what it says in the AC 43,13 :


6-17. INTERGRANULAR CORROSION.
Inter-granular corrosion is an attack on the grain boundaries of a metal. A highly magni- fied cross section of any commercial alloy shows the granular structure of the metal. It consists of quantities of individual grains, and each of these tiny grains has a clearly defined boundary which chemically differs from the metal within the grain. The grain boundary and the grain center can react with each other as anode and cathode when in contact with an electrolyte.
(See figure 6-9.)
Rapid selective corrosion of the grain boundaries can occur. High-strength aluminum alloys such as 2014 and 7075 are more susceptible to inter-granular corrosion if they have been improperly heat-treated and then exposed to a corrosive environment.

6-18. EXFOLIATION CORROSION. Ex- foliation corrosion is an advanced form of in- ter-granular corrosion and shows itself by lift- ing up the surface grains of a metal by the force of expanding corrosion products occur- ring at the grain boundaries just below the sur- face. (See figure 6-10.) It is visible evidence of inter-granular corrosion and is most often seen on extruded sections where grain thick- ness are usually less than in rolled forms.It is visible evidence of inter-granular corrosion and is most often seen on extruded sections where grain thickness are usually less than in rolled forms.
Thanks Tom, excellent reference; been a long time since I looked at that. So any alloy family is susceptible but it is the heat of the grade that makes for Intergranular activity. The effect itself is electrolytic because aluminum is a poorly behaved metal; it is easy to work with though. If you heat incorrectly you set up a potential charge for a battery within the grain structure of the alloy just waiting for some electrolyte to turn it loose. This ends up with a fizzing of the area on the edge of each grain.

It's the exfoliation which is an advanced feature of the reaction brought about by the pressure of the forging process. 50,000 tons of weight bearing down. That's how they achieved it, just stacks of mass, Iron for the most part. From the looks of the one I attached it appears as a steam actuated, cam driven, mechanically raised structure and stack of weights.
__________________
Quote:
There is enough for everyone; there is never enough for the greedy.-Mahatma Gandhi

All life is precious, the problem is there is just too much of it.-Dali Lama
Henning is offline   Reply With Quote
Old May 5th, 2012, 04:43 AM
Posted in reply to Henning's post "Re: Corrosion.."
  #97
FBH N801BH is offline
(User ID: N801BH)
Final Approach
 
N801BH's Avatar
 
Join Date: Jul 2008
Location: Jackson Hole Wy
Posts: 9,779
Send a message via Yahoo to N801BH
Re: Corrosion..

Quote:
Originally Posted by Henning View Post
..... From the looks of the one I attached it appears as a steam actuated, cam driven, mechanically raised structure and stack of weights.
I can just picture a OSHA sign attached to it with the warning that says "Pinching Hazzard"..
__________________
Ben
Jackson Hole Wy.
www.haaspowerair.com
N801BH is offline   Reply With Quote
Old May 5th, 2012, 08:10 PM
Posted in reply to Henning's post "Re: Corrosion.."
  #98
Cap'n Jack Cap'n Jack is offline
(User ID: Cap'n Jack)
En-Route
 
Cap'n Jack's Avatar
 
Join Date: Jun 2006
Location: Nebraska
Posts: 4,341
Re: Corrosion..

Quote:
Originally Posted by Henning View Post
50,000 tons of weight bearing down. That's how they achieved it, just stacks of mass, Iron for the most part. From the looks of the one I attached it appears as a steam actuated, cam driven, mechanically raised structure and stack of weights.
Company that owns it now claims it's hydraulic.

http://www.wymangordon-grafton.com/f...abilities.html
Cap'n Jack is offline   Reply With Quote
Old May 14th, 2012, 11:18 PM
Posted in reply to Cap'n Jack's post "Re: Corrosion.."
  #99
3934V Tom-D is offline
(User ID: Tom-D)
Touchdown! Greaser!
 
Join Date: Feb 2005
Posts: 16,288
Re: Corrosion..

I finally got to see the cleaned up cabin former today. Basically no serious damage, primed it and that's all it required.

We installed new BAS shoulder harness and sent him home to install his new head liner.

I didn't get pictures, forgot the camera.
Tom-D is offline   Reply With Quote
Old May 14th, 2012, 11:46 PM
Posted in reply to Cap'n Jack's post "Re: Corrosion.."
  #100
iHenning Henning is offline
(User ID: Henning)
Taxi to Parking
 
Henning's Avatar
 
Join Date: Feb 2005
Location: Ft Lauderdale FL
Posts: 42,589
Re: Corrosion..

Quote:
Originally Posted by Cap'n Jack View Post
Company that owns it now claims it's hydraulic.

http://www.wymangordon-grafton.com/f...abilities.html
Question in my mind is are the hydraulics openning the press or closing it. It would seem to me using them to open the press an let the weight forge would do a better job. Neat stuff though, big old machines still knocking out parts.
__________________
Quote:
There is enough for everyone; there is never enough for the greedy.-Mahatma Gandhi

All life is precious, the problem is there is just too much of it.-Dali Lama
Henning is offline   Reply With Quote
Reply
Home Register New Posts Today's Posts
Go Back   Pilots of America Message Board > Controlled Airspace > Maintenance Bay

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Corrosion areas on a Skyhawk? cbmontgo Maintenance Bay 9 September 15th, 2011 07:26 PM
Corrosion in the carb Tom-D Maintenance Bay 10 November 10th, 2010 05:49 PM


All times are GMT -4. The time now is 07:26 AM.


Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
(c) 2005 - Pilots of America