Corrosion..

[Tom-D]

Over the weekend I was completing an Annual on a 170, and was to install a new headliner. After the old head liner was out this is what I found.

Rear Cabin bulkhead where Cessna used glue to attach the OEM headliner

What would you want me to do with it?

 

[somorris]

I would want it cleaned up and fixed. Corrosion is one of my biggest worries and an aircraft owner. Then again, with aluminum, what is the chance of that continuing to get worse or just staying like that? Since it is a 172 and the headliner was OEM, it has probably been like that a long time. Who is to say it wouldn't continue like that and get no worse until you and I are long gone?

 

[Piloto]

Typical of old airframes were the structure has not been coated with zinchromate. Does not appear to be a serious condition, just surface corrosion. Sand off the affected surfaces, clean it very well with MEK and apply zinchromate. If possible clean and apply zinchromate to the whole structure to prevent future damage.

José

 

[Tom-D]

I would want it cleaned up and fixed. Corrosion is one of my biggest worries and an aircraft owner. Then again, with aluminum, what is the chance of that continuing to get worse or just staying like that? Since it is a 170 and the headliner was OEM, it has probably been like that a long time. Who is to say it wouldn't continue like that and get no worse until you and I are long gone?

The headliner I took out is the second one.

 

[somorris]

What are your thoughts, Tom?

 

[Tom-D]

I would want it cleaned up and fixed. Corrosion is one of my biggest worries and an aircraft owner. Then again, with aluminum, what is the chance of that continuing to get worse or just staying like that? Since it is a 172 and the headliner was OEM, it has probably been like that a long time. Who is to say it wouldn't continue like that and get no worse until you and I are long gone?

You never sand on Cessna structure, you etch to remove all corrosion products, and re-enforce as required.

Cabin former(bulkheads) are structure in the 100 series.

 

[Tom-D]

What are your thoughts, Tom?

Seeing as it will require 3-4 days work to clean up the corrosion, I sent the owner on his way, to clean it up him self.
When he is ready to repair/or preserve the area I'll inspect and we can replace the head liner, and he can sign it off him self.

no sense eating up his wallet for me to do the labor when he is capable.

 

[N801BH]

Seeing as it will require 3-4 days work to clean up the corrosion, I sent the owner on his way, to clean it up him self.
When he is ready to repair/or preserve the area I'll inspect and we can replace the head liner, and he can sign it off him self.

no sense eating up his wallet for me to do the labor when he is capable.

If he can sign it off himself, why did he need you to do the annual ?

 

[Let'sgoflying!]

Only an ia can sign the annual, owner can do P.M. and sign that off.

 

[N801BH]

Only an ia can sign the annual, owner can do P.M. and sign that off.

I do know that.... it was the statement Tom made "Cabin former(bulkheads) are structure in the 100 series.", that had me curious.. If he feels the component is structural then that forbids owner maintenance.

 

[Let'sgoflying!]

ah - got it, Ben. Can't speak for Tom...maybe he thinks its minor enough to be owner-P.M.?

 

[Tom-D]

If he can sign it off himself, why did he need you to do the annual ?

the head liner has nothing to do with the annual.

simply a discrepancy that an owner can repair under CFR 43-A (c)
Preventive maintenance the owner can clean and treat corrosion even on structure.

 

[Henning]

Over the weekend I was completing an Annual on a 170, and was to install a new headliner. After the old head liner was out this is what I found.

Rear Cabin bulkhead where Cessna used glue to attach the OEM headliner

What would you want me to do with it?

Hard to tell, how's it feel when you poke it with an awl?

 

[Tom-D]

Hard to tell, how's it feel when you poke it with an awl?

I'd simply rather see it when it is cleaned up and see what a scratch gauge measures, to see if we need a repair.

I really don't want to do more damage than has already been done.

 

[Henning]

I'd simply rather see it when it is cleaned up and see what a scratch gauge measures, to see if we need a repair.

I really don't want to do more damage than has already been done.

If I can poke an awl through it now I can save all that clean up expense because no clean up will make it pass. Why waste money and time?

 

[Tom-D]

If I can poke an awl through it now I can save all that clean up expense because no clean up will make it pass. Why waste money and time?

Until you know where the deepest pit is you are simly guessing as to where to stick the awl.

I'll wait. Down time is not an issue.

 

[Henning]

Until you know where the deepest pit is you are simly guessing as to where to stick the awl.

I'll wait. Down time is not an issue.

Wasn't a guaranty, just a dozen taps to see if it's worth cleaning. If not, there's a 75%+ chance I'll find enough to shut down in that dozen taps.

 

[Tom-D]

Wasn't a guaranty, just a dozen taps to see if it's worth cleaning. If not, there's a 75%+ chance I'll find enough to shut down in that dozen taps.

You must remove the corrosion before you will know what to do.

We are sure enough not going to remove and replace the whole aft cabin former, That requires a fuselage jig, with the wings off, and parts, which will have a good chance of being as bad as this one. cost?? around $13- $15k, good possibility that this will clean up with no need for a repair, and can be protected with a coat of zink cromate primer.

then the head liner can go in with no worries later.

 

[CMTowner]

I would clean up the corrosion the best I could and then apply either corrosion-x or ACF-50. The Zinc primers don't really have any corrosion prevention properties.


---
I am here: http://tapatalk.com/map.php?pdjp4l

 

[kyleb]

The Zinc primers don't really have any corrosion prevention properties.

They are very effective corrosion preventatives. About the only thing better is epoxy over properly prepared metal, and you can't get epoxy in a spray can...

 

[DouglasBader]

Typical of old airframes were the structure has not been coated with zinchromate. Does not appear to be a serious condition, just surface corrosion. Sand off the affected surfaces, clean it very well with MEK and apply zinchromate. If possible clean and apply zinchromate to the whole structure to prevent future damage.

Zinc Chromate peels. It doesn't prevent corrosion.

Don't sand those sufaces. Don't sand anything in the aircraft. Abrasive materials of certain kinds may be used, depending on what's found, but the first step is to clean the area.

If you go sanding the structure, you may embed particles in the structure which can lead to considerably more corrosion and cracking, as well as embrittlement. Don't do that. Only certain abrasive materials should be used, and long before you make that decision, you need to know what the extent of the damage is. Clean the area very thoroughly.

Conversion treatments and surface treatments are a first step once it's cleaned and prepared; alodining the material is far more important than chromate (if you can find chromate: most of what's billed as zinc chromate these days isn't).

Treatment with Corrosion X or other penetrating chemicals isn't going to fix the problem.

Clean it.
Inspect it.
Treat it.
Reinforce it.
Do the paperwork.

 

[Piloto]

Zinc Chromate peels. It doesn't prevent corrosion.

Don't sand those sufaces. Don't sand anything in the aircraft. Abrasive materials of certain kinds may be used, depending on what's found, but the first step is to clean the area.

If you go sanding the structure, you may embed particles in the structure which can lead to considerably more corrosion and cracking, as well as embrittlement. Don't do that. Only certain abrasive materials should be used, and long before you make that decision, you need to know what the extent of the damage is. Clean the area very thoroughly.

Conversion treatments and surface treatments are a first step once it's cleaned and prepared; alodining the material is far more important than chromate (if you can find chromate: most of what's billed as zinc chromate these days isn't).

Treatment with Corrosion X or other penetrating chemicals isn't going to fix the problem.

Clean it.
Inspect it.
Treat it.
Reinforce it.
Do the paperwork.

The use of zinc-hromate for aircraft corrosion prevention is very well known and documented. Check http://www.colorserver.net/history/history-zinc-chromate.htm

Sanding off the surface by hand with sand paper #100 or finer to remove surface corrosion and cleaning the dust with MEK is a common procedure at the MROs, repair shops and manufacturing facilities. On complex surfaces brushing is also used. The surface corrosion needs to be removed completely so the zinc-chromate will bond effectively to the bare metal. Alodine is an option but make sure there is no residue since it will impair zinc-chromate or other coating proper bonding.

José

 

[DouglasBader]

Sanding off the surface by hand with sand paper #100 or finer to remove surface corrosion and cleaning the dust with MEK is a common procedure at the MROs, repair shops and manufacturing facilities. On complex surfaces brushing is also used. The surface corrosion needs to be removed completely so the zinc-chromate will bond effectively to the bare metal. Alodine is an option but make sure there is no residue since it will impair zinc-chromate or other coating proper bonding.

A surface that's properly conversion treated, such as Alodine, doesn't need chromate.

Treating a surface with chromate is no substitute for properly treating the surface.

As for sanding, don't do it, as in NO!!!!!!!!!!!!!!!!!!!

When you say "brushing" of surfaces, hopefully you don't mean wire brushing. Again, that's a big NO!!!!!!!!!!!!!!

One doesn't remove surface corrosion then paint with zinc chromate. One removes surface corrosion then treats as needed. If chromate is to be applied, it's done after the metal is properly treated. Simply removing the corrosion then shooting the area with chromate is a poor practice, and is most definitely NOT industry standard.

"Sand paper" is a term that's sometimes used by people who don't know better or the difference. At best you might refer to it as "abrasive paper," but there are a number of differences in products used for the abrasive properties, and when it comes to "sanding" metal, you're far, far better off using other preparatory abrasives which do not embed the material with corrosion-causing agents. Scotchbrite is among the preferred materials used for abrading aluminum. Bead blasting with appropriate media such as corn is also preferred.

Surface preparation is always important, whether painting or treating. One should never paint, including etching primers and chromates and epoxies, before the surface is properly prepped and treated.

 

[Piloto]

A surface that's properly conversion treated, such as Alodine, doesn't need chromate.

Treating a surface with chromate is no substitute for properly treating the surface.

As for sanding, don't do it, as in NO!!!!!!!!!!!!!!!!!!!

When you say "brushing" of surfaces, hopefully you don't mean wire brushing. Again, that's a big NO!!!!!!!!!!!!!!

One doesn't remove surface corrosion then paint with zinc chromate. One removes surface corrosion then treats as needed. If chromate is to be applied, it's done after the metal is properly treated. Simply removing the corrosion then shooting the area with chromate is a poor practice, and is most definitely NOT industry standard.

"Sand paper" is a term that's sometimes used by people who don't know better or the difference. At best you might refer to it as "abrasive paper," but there are a number of differences in products used for the abrasive properties, and when it comes to "sanding" metal, you're far, far better off using other preparatory abrasives which do not embed the material with corrosion-causing agents. Scotchbrite is among the preferred materials used for abrading aluminum. Bead blasting with appropriate media such as corn is also preferred.

Surface preparation is always important, whether painting or treating. One should never paint, including etching primers and chromates and epoxies, before the surface is properly prepped and treated.

Doug

You are a contradicting guy. First you say not to sand and then you recommend different abrasive materials. Then you first mention not to use zinc-chromate then you say to prepare surface before zinc-chromate is applied. Are you a politician?

José

 

[DouglasBader]

You are a contradicting guy. First you say not to sand and then you recommend different abrasive materials. Then you first mention not to use zinc-chromate then you say to prepare surface before zinc-chromate is applied. Are you a politician?

No, I'm not a politician. I'm a fairly experienced aircraft mechanic and inspector, however. You, clearly, are not.

You don't understand the difference between "sanding" and the use of an abrasive medium such as a scotchbrite wheel or rolex wheel?

You don't understand that the use of the word "sanding" marks you as very ignorant of the topic?

Do a little research, then post back.

As for the use of zinc chromate: I didn't say one shouldn't use it. I did say that it does NOT take the place of proper surface treatment. Further, I also stated that proper preparation is necessary in all cases. Further, I did state that whereas chromate is not a corrosion treatment nor prevention method, surface conversion treatment is.

If you go sanding, especially with "sandpaper," you're more likely to cause corrosion than you are to solve any problem that may be facing you at the time. You could be causing some very serious problems down the line.

 

[Let'sgoflying!]

well, we could argue all night or we could just refer to the bible to see what it has to say about sanding.

 

[DouglasBader]

Table 6-1 in AC 43.13 1B cites the use of (not sand paper) abrasive paper or cloth using aluminum oxide, or garnet, though I don't know anyone who would use garnet, and very few today who would use other than a scotchbrite material.

 

[Piloto]

Table 6-1 in AC 43.13 1B cites the use of (not sand paper) abrasive paper or cloth using aluminum oxide, or garnet, though I don't know anyone who would use garnet, and very few today who would use other than a scotchbrite material.

So what is the difference between sand paper and abrasive paper. After all you never recommended any paper or sanding procedure, like it is indicated on the above table. How would you work with abrasive paper if it is not to be used for sanding?

José

 

[Let'sgoflying!]

Table 6-1 in AC 43.13 1B cites the use of (not sand paper) abrasive paper

I believe most people use the term sand paper generically to indicate a paper holding an abrasive, not necessarily silicates.

edit -
Here:
http://dictionary.reference.com/browse/sand+paper?s=t
sand·pa·per
   [sand-pey-per] Show IPA
noun
1.
strong paper coated with a layer of sand or other abrasive,

 

[DouglasBader]

So what is the difference between sand paper and abrasive paper. After all you never recommended any paper or sanding procedure, like it is indicated on the above table. How would you work with abrasive paper if it is not to be used for sanding?

Well, one difference is that people who don't know what they're talking about around aircraft in the shop refer to abrasive cloths and papers as "sandpaper." That's a good start.

Given the number of different abrasive materials available, and given that many of them cannot and should not be used on aircraft for certain applications, referring to abrasives used in corrosion control as "sandpaper" is much like referring to fuel in the tank as "gas." Is it 100LL, Jet A, Mogas, Diesel, or other? Specifics in aircraft maintenance are important.

Previously you seemed confused when considering the abrasive properties of scotchbrite vs. "sandpaper."

It's little wonder that you don't think there's a difference. You really don't have a clue, do you? Given that you don't have a clue, why dole out maintenance counsel concerning a subject about which you clearly know nothing?

 

[Piloto]

Well, one difference is that people who don't know what they're talking about around aircraft in the shop refer to abrasive cloths and papers as "sandpaper." That's a good start.

Given the number of different abrasive materials available, and given that many of them cannot and should not be used on aircraft for certain applications, referring to abrasives used in corrosion control as "sandpaper" is much like referring to fuel in the tank as "gas." Is it 100LL, Jet A, Mogas, Diesel, or other? Specifics in aircraft maintenance are important.

Previously you seemed confused when considering the abrasive properties of scotchbrite vs. "sandpaper."

It's little wonder that you don't think there's a difference. You really don't have a clue, do you? Given that you don't have a clue, why dole out maintenance counsel concerning a subject about which you clearly know nothing?

Dough, I have been an aircraft and boat owner for over 40 years. I used to own a Striker 44 cabin cruiser with aluminum hull, dock at a marina in Fajardo, PR. And believe me a boat in salt water will teach you everything about corrosion. In addition I was a systems engineer at Zhukovsky for the Beriev-200 amphibious during the JAA certification program. And a systems engineer at United SFO MRO responsible for the upgrade of the old classics (B727, DC-9, DC-10, B747-200, B737-200). Which BTW had plenty of corrosion problems.

My experience in life has been to never under estimate the background or experience of the guy on the other side. Take it from an old man.

José

 

[DouglasBader]

You're not a mechanic, then? That's all you needed to say. Don't know what you're talking about. That's good enough.

Being a boat owner doesn't make you an aircraft mechanic. Neither does being a systems engineer.

By all means, give counsel on engineering systems.

Refrain from talking about things you don't understand. Certainly treating corrosion and working on aircraft are two of those things. You should probably stick to boats.

 

[Piloto]

You're not a mechanic, then? That's all you needed to say. Don't know what you're talking about. That's good enough.

Being a boat owner doesn't make you an aircraft mechanic. Neither does being a systems engineer.

By all means, give counsel on engineering systems.

Refrain from talking about things you don't understand. Certainly treating corrosion and working on aircraft are two of those things. You should probably stick to boats.

No I am not a mechanic but used to supervise 7 APs and 8 technicians on the upgrade of the classics at United MRO. You should have seen what lavatories corrosion is like on an airframe. And yes we had plenty of sand paper to treat it.

José

 

[Tom-D]

I hope every one knows the 43,13 is not the proper reference to do any repairs to a Cessna or Piper or any aircraft that has a structural repair manual.

 

[Let'sgoflying!]

Yes, we know - you have told us many times. Thanks again for the reminder, Tom.

 

[Tom-D]

Yes, we know - you have told us many times. Thanks again for the reminder, Tom.

OK then, tell me what is the proper method of removing corrosion from structure in a C-170, like this?

 

[DouglasBader]

No I am not a mechanic but used to supervise 7 APs and 8 technicians on the upgrade of the classics at United MRO. You should have seen what lavatories corrosion is like on an airframe. And yes we had plenty of sand paper to treat it.

You're not a mechanic, and you used to supervise people cleaning toilets. Got it.

You've gone on about your high qualifications as a "systems engineer," and now you're down to supervising people cleaning toilets.

The extent of your qualification is an associate degree, is it not? You were an international systems engineer advising the biggest firms in the world, working on the biggest projects, and held yourself out as an expert in corrosion treatment, control, and repairs as a "systems engineer," and your expertise goes as far as group supervisor in a toilet cleaning crew, working off your associate degree...and you're presuming to give counsel on how to perform aircraft maintenance.

Very rich, indeed.

 

[Piloto]

You're not a mechanic, and you used to supervise people cleaning toilets. Got it.

You've gone on about your high qualifications as a "systems engineer," and now you're down to supervising people cleaning toilets.

The extent of your qualification is an associate degree, is it not? You were an international systems engineer advising the biggest firms in the world, working on the biggest projects, and held yourself out as an expert in corrosion treatment, control, and repairs as a "systems engineer," and your expertise goes as far as group supervisor in a toilet cleaning crew, working off your associate degree...and you're presuming to give counsel on how to perform aircraft maintenance.

Very rich, indeed.

Doug

My 2 cents advise. Never try to denigrate others in public. It looks bad on you. Take it from an old man. As for cleaning toilets I have a lot of respect for those involved in it. Without them this would be a dirty infected society.

José

 

[gprellwitz]

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[Let'sgoflying!]

OK then, tell me what is the proper method of removing corrosion from structure in a C-170, like this?

Why certainly, Mr. Tom! One would simply refer to chapter on corrosion treatment and control in the "Cessna 170 Structural Repair Man...........hey this isn't another of your trick questions is it?! I am guessing there exists no such book!
In any case, never would I feign to have any knowledge approaching yours in this department. Do tell! High speed wire wheel? H2SO4 bath? Steel scouring pad?


PS Thanks, Grant.