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Topic: What would cause the metal on this fitting to flak apart? (Read 2027 times) previous topic - next topic

What would cause the metal on this fitting to flak apart?

The pictured fitting is part of one of the two air cylinders that moves the step in and out.  The other cylinder is fine.  I also added a picture of the flaked off metal. 

What's going on?

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Re: What would cause the metal on this fitting to flak apart?

Reply #1 –
Not seeing any pics Larry. 

Re: What would cause the metal on this fitting to flak apart?

Reply #2 –
pictures

Re: What would cause the metal on this fitting to flak apart?

Reply #3 –
Some sort of corrosion,could it be a cheap chinese replacement?

Re: What would cause the metal on this fitting to flak apart?

Reply #4 –
Is this on the step or the floor slide in front of the passengers seat? That dose look like corrosion on the cylinder.

Re: What would cause the metal on this fitting to flak apart?

Reply #5 –
Quote
could it be a cheap chinese replacement?

The cylinder is original to the coach.

Quote
Is this on the step or the floor slide in front of the passengers seat?

On the step.  This is a 2004 model. The cylinders are mounted below the step but not directly exposed.  They are covered by a panel that is open on the sides facing the sides of the coach.  The one that is bad is toward the front of the coach.  So the cylinder is not completely sealed from the outside but it is covered.  I don't see any build up of dirt and the rest of the cylinder has only minimal wear you'd expect. 

Re: What would cause the metal on this fitting to flak apart?

Reply #6 –
So if pinpointing the cause may not be easy, what treatment to the metal that will prevent further flaking?  Simple thing would be to wire brush, then clean and degrease with baking soda, then paint it. 

Re: What would cause the metal on this fitting to flak apart?

Reply #7 –
Spray some soapy water on the fitting and see if it is leaking. I could be coming from the air desiccant. 

Re: What would cause the metal on this fitting to flak apart?

Reply #8 –
May be just a bad batch of metal,clean and try some Rust Bullet brush on paint,you can get it on Amazon in a 4 oz. can.

Re: What would cause the metal on this fitting to flak apart?

Reply #9 –
Quote from: craneman –
Spray some soapy water on the fitting and see if it is leaking. I could be coming from the air desiccant. 

My thoughts exactly. 
Larry are the metal flakes magnetic?

Re: What would cause the metal on this fitting to flak apart?

Reply #10 –
That appears to be intergranular corrosion, often due to the type of alloy metals.

Re: What would cause the metal on this fitting to flak apart?

Reply #11 –
Quote from: sedelange –
That appears to be intergranular corrosion, often due to the type of alloy metals.
If the material is stainless steel, I agree.

Stainless steel has a very thin and stable oxide film rich in chrome. This film reforms rapidly by reaction with the atmosphere if damaged. If stainless steel is not adequately protected from the atmosphere during welding or is subject to very heavy grinding operations, a very thick oxide layer will form. This thick oxide layer, distinguished by its blue tint, will have a chrome-depleted layer.
 https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=239

Re: What would cause the metal on this fitting to flak apart?

Reply #12 –
If it was from the desiccant you would see other problems,the step is the farthest from the air drier.Regardless of what it is it is an
isolated incident,we'll never know exactly why this happened.

Re: What would cause the metal on this fitting to flak apart?

Reply #13 –
Quote from: sedelange –
That appears to be intergranular corrosion, often due to the type of alloy metals.

Bingo! Give that man a cigar.  The material is known generically as Die Cast referring both to the process used to make the part and the material used. The base material is Zinc with additions and the material is a solution not a mixture.  When cooled distinct granules form and under a surprising number of mild conditions intergranular corrosion forms prying the pieces apart.

Corrosion Resistance | Die Casting Alloys | Die Casting Company

P.S. I didn't eat all of those books for nuthin'

Re: What would cause the metal on this fitting to flak apart?

Reply #14 –
Quote
are the metal flakes magnetic?
Yes, but not very much.  The nut next to the fitting is much more magnetic.  The cylinder tube and this fitting are much less.

Quote
Spray some soapy water on the fitting and see if it is leaking
No leaking.

If it is intergranular corrosion, it took 15 years to get to this state.  It looks like I can wire brush it down to a level that looks good.  I could do that and then clean and paint it (and check it yearly). 

Or is the part compromised and should be replaced?  It's really not in a "critical" area that will leave me stranded if it fails.

Thanks for the expert knowledge folks!!!

Re: What would cause the metal on this fitting to flak apart?

Reply #15 –
Quote from: Larry Rubin –
Yes, but not very much.  The nut next to the fitting is much more magnetic.  The cylinder tube and this fitting are much less.
No leaking.

Well I guess that rules out desiccant then.

Re: What would cause the metal on this fitting to flak apart?

Reply #16 –
Quote from: Larry Rubin –


If it is intergranular corrosion, it took 15 years to get to this state.  It looks like I can wire brush it down to a level that looks good.  I could do that and then clean and paint it (and check it yearly). 

Thanks for the expert knowledge folks!!!

If you have the air cylinder out far enough to wire brush and paint, why not replace it with a new one.  Then you can check it off for the next 15 years.

As far as thanks for the knowledge, I just want to remind you that you get what you pay for . . .

Art

Re: What would cause the metal on this fitting to flak apart?

Reply #17 –
"If it is intergranular corrosion, it took 15 years to get to this state.  It looks like I can wire brush it down to a level that looks good.  I could do that and then clean and paint it (and check it yearly)."
That is what I would do. It isn't leaking and doesn't look that bad in the pictures. Ok my aircraft background would have me treat both of the cylinders to prevent further problems. I would probably spend some time under there cleaning and painting any outher rust/corrosion I found. ^.^d
Bill

Re: What would cause the metal on this fitting to flak apart?

Reply #18 –
"I would probably spend some time under there cleaning and painting any outher rust/corrosion I found. "

That's exactly what I've been doing all morning.  Lots of fun. 

Re: What would cause the metal on this fitting to flak apart?

Reply #19 –
Quote from: Larry Rubin –

Or is the part compromised and should be replaced?  It's really not in a "critical" area that will leave me stranded if it fails.

Thanks for the expert knowledge folks!!!

It take air that is also used to stop the coach with.  If it starts leaking bad enough you might not have enough air to stop or it will slow you down as the lack of air pressure will cause the parking brake to applying