Rust proofing steel tube?

[Marty_d]

Hey all,

 

I'm at the stage of cutting and installing the wing struts.  These are seamless chrome moly tubes.

I've cleaned up and sprayed the outside of the first one with etch primer, and now I'm thinking about the inside.  

What's the best way to rust proof the inside of steel tubes, that aren't sealed on the ends and are on the outside of the aircraft?

 

Thanks in advance.

Cheers, Marty

[KRviator]

In the RV with the push/pull tubes, I ran a bit of string through the tube and tied a small sponge to it. Poured etch primer in at the sponge end, then pulled it through, "painting" the inside with the sponge. Repeat as often as needed till you're comfortable 'enough' has been painted to coat the interior.

[BrendAn]

8 minutes ago, Marty_d said:

Hey all,

 

I'm at the stage of cutting and installing the wing struts.  These are seamless chrome moly tubes.

I've cleaned up and sprayed the outside of the first one with etch primer, and now I'm thinking about the inside.  

What's the best way to rust proof the inside of steel tubes, that aren't sealed on the ends and are on the outside of the aircraft?

 

Thanks in advance.

Cheers, Marty

powder coating ?

[Marty_d]

Thanks KR, the sponge on a string is a good idea.  Given it's open at one end, I could probably use a sponge attached to a smaller diameter tube as well.

 

Brendan - good idea, but the spars are around 2m long so cost might be an issue. 

[Blueadventures]

20 minutes ago, KRviator said:

In the RV with the push/pull tubes, I ran a bit of string through the tube and tied a small sponge to it. Poured etch primer in at the sponge end, then pulled it through, "painting" the inside with the sponge. Repeat as often as needed till you're comfortable 'enough' has been painted to coat the interior.

And then do same with ACF50 at times say twice a year.

[onetrack]

Marty - Cortec make a huge range of VpCI (Vapour Phase Corrosion Inhibitors) that are each specifically designed for particular uses.

 

I suggest you contact them and inquire as to which of their products they recommend for your intended use.

 

I use several of their VpCI products in my workshop and they're all very good.

 

Products

WWW.CORTECVCI.COM

---

Cortec® Product Information Product Life CycleCorrosion Chart VpCI® Total Corrosion Control How VCI Works Click on the links below to access product descriptions and other information regarding various...

 

[Thruster88]

You could get some corks and put say 500ml paint in sloshing it. Stand on end to drain excess paint.

[skippydiesel]

11 hours ago, Blueadventures said:

And then do same with ACF50 at times say twice a year.

Or Tectyl  liquid/sprayable wax used in automotive rust prevention.

[cherk]

.....or Fishoilene .....penetrates and dries like varnish but slightly flexable

[facthunter]

Paint with ZINC in it gives Galvanic protection..   Nev

[Kenlsa]

I did the tubing on my Colt using Linseed oil.  It is an approved method.

 

Ken

[Blueadventures]

6 minutes ago, Kenlsa said:

I did the tubing on my Colt using Linseed oil.  It is an approved method.

 

Ken

Skyfox is the same; however sealed tubes not open.

[LoonyBob]

The Taylorcraft & Austers used Linseed oil (as Kensla said, it's Approved).  VH-WRB had no corrosion whatsoever inside it after the bowser incident at Bathurst (I thinkthat was WRB?). but it wa sonly about 33 years old then.

Be aware! In Tymes of Olde, Boiled Linseed oil was ordinary linseed oil, brought to the boil & simmered to drive all the moisture off/reconfigure the volatiles; and it dried as a completely impervious film. Bunnings "Boiled Linseed" is linseed oil cut with a thinner, and dries porous. A good artist supplier will sell fair dinkum boiled linseed; pricey, but not compared to the alternatives.

 

Linseed has the advantage of being self-healing. i've used unboiled linseed, both straight and 50/50 with fish oil, in car sills (which are ventilated), and either stops any further rusting for a decade or so.

[facthunter]

ZINC based Paint gives you galvanic protection, Not just a physical barrier.  Nev

[onetrack]

The latest protective chemicals and paints far exceed any older "tried and tested" products such as linseed oil. I use a local rust-proofing paint called Metalfix, produced by Phoenix Paints.

It was put together by a bloke who is a chemist, and its based on phosphoric acid technology. The paint chemically bonds to metals and even any rust present, to provide an impermeable coating.

This paint withstands up to 1000°, making it virtually fireproof as well. The best part is, it's water based and lasts forever, you just thin it with a little more water, if its gone to a too-thick consistency.

I've seen a Landcruiser painted with Metalfix, that was being used to haul boats out of the ocean on a daily basis, and even after 10 years of this work, there was no corrosion.

The only problem is the paint is breathtakingly costly, but if you need maximum corrosion protection, you can't beat it.

 

https://www.phoenixpaints.com.au/products/primer-coats/metalfix/

 

[Marty_d]

No distributors in Tas by the looks of it, OT.

 

[Blueadventures]

1 hour ago, Marty_d said:

No distributors in Tas by the looks of it, OT.

 

Business opportunity????

[Marty_d]

I don't think people will want to come 20km south of Hobart then down our steep & dodgy driveway for a tin of paint.

[skippydiesel]

My observations:

 

All the oil/liquid wax corrosion preventers :

• Can be applied to almost any dry surface without much in the way of preparation, painted/unpainted - SHOULD NOT BE APPLIED OVER WET SURFACES/CAVITIES as may trap moisture, 
• Dry to a waxy finish (ie not like paint). Finish may attract dust for a sustained period.
• Self healing ie scratch will close over
• Have good to excellent penetrating qualities
• Can be sprayed or painted - most can be thinned (if need be) for spraying with a putty gun. Cavities are best treated with a flexible tube fitted with side jets,  on the gun.
• Durable ie will last quit a long time (could be 10 years + for some - will depend on product & exposure). May require follow up treatment for best protection.
• Messy but usually minimal toxicity 
• Can be thinned with most thinners (even turps) - follow instructions for best thinner & ratios
• Cost effective - a little goes a long way
• May be heavy for aviation use
• Most can not be successfully painted over

Chemical bonding paint types (some undercoats):

• Need to religiously follow surface preparation & curing/drying instructions.
• Care should be taken to determine chemical compatibility with surface to be treated.
• Tend to be expensive
• Usually toxic - good quality PPE required
• Light weight
• Durable but unlikly to be self healing. Likely to last the service life of the aircraft.
• Top coat compatibility should be checked before purchase.
• Likely to be a two pack system, requiring accurate mixing ratios.
• May adhere to spray/mixing equipment making them unusable for other paints. 

 

[onetrack]

And that's the beauty of the Metalfix paint - non-toxic, water-based, only basic preparation required, compatible with any type of carbon steel, no need for complex preparation/curing/drying times, can be painted over with all types of paint. Can be brushed or sprayed on.

[skippydiesel]

"compatible with any type of carbon steel,"

 

What about other metals/alloys??

[onetrack]

Well, Metalfix is phosphoric acid based, so if phosphoric acid is capable of reacting with the base metal, it will bond to it. This does mean it will bond to galvanised metal and aluminium. It will also bond to timber and fibreglass, and can be used to patch holes in gutters, tanks and roofs. Click on "Product Applications" in the link below to see plenty of application photos.

 

Metalfix | Phoenix Paints

WWW.PHOENIXPAINTS.COM.AU

 

Edited February 23 by onetrack

[Reynard]

Yep, phosphoric acid, which you can get at Bunnings. For chrome moly it acts more as an anodic inhibitor.

[facthunter]

There's more than one type of Phosphoric acid. it's rather complex chemistry. Nev

[onetrack]

Yes, there is more than one type chemically, if you want to be pedantic - but the common "phosphoric acid" you can buy nearly anywhere is correctly named orthophosphoric acid, but it's always simply called "phosphoric acid".

It comes in various forms and combinations, you can buy it in a jelly format, where it's called "naval jelly", or called "mag wheel cleaner", "aluminium cleaner", and it's also found under about twenty different brand names.

But you'd find it difficult to purchase the other chemical varieties of phosphoric acid, because they're not readily available, and they're mostly confined to laboratory operations.

The greatest variation in products found is the percentage of phosphoric acid in the solution. Some are pretty weak, some have a high percentage of phosphoric acid in them. Ranex is one of the stronger varieties.

Phosphoric acid is added to a number of paints, it's added to "etch primer" to assist in chemical bonding of the paint, and to neutralise any light surface rust.