Preventing rust inside steel pipe or tubing?

Monocoque metal, mostly yes these days; frame & skin, no because aluminum is structurally inefficient as a frame.

Split pipe rub rails are most often just sealed voids. Sometimes they are filled with pitch & pine, but even then they are sealed.

 

Very interesting, particularly as I am about to add some new suggestions about utilizing steel pipe for 'floatation tubes' over on this floating cottage/houseboat subject thread:
http://www.boatdesign.net/forums/boat-design/retirement-houseboat-floating-home-23987-12.html

I'll likely make a link back to your posting here,...or you could add such a posting to that subject thread after I add my new material?

 

What I bought is spray foam that is expanding, and closed cell.

Since it will compress inside the pipe, there will not be any gaps anywhere.
Since it's closed cell, air will not flow through it.

What could possibly go wrong? I can't imagine?

If theres a tight seal, no air, how can rust start?

 

Just do it.

 

Never thought of it before, but are the bubbles in the foam air or some other gas? Most aerosols use propane as a propellant, is that whats in foam bubbles?

 

Can you expand on this a bit more?

What would you expect of 'natural gas pipe' that is fully closed off, and then utilized for a floating device?

 

I suppose you are talking about single part foam? Since the foam will push the air ahead of it in the tube, will there be sufficient moisture remaining in the tube to effect a cure?
I have had to gouge out two part foam insulation from steel trawler fish holds several times for access to the hull plate. Even where the foam has been long term saturated on the internal face, the steel has been perfect underneath after nearly 30 years with only the original weld primer coating.

 

What could possibly go wrong? I can't imagine?

If theres a tight seal, no air, how can rust start?
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Yes, without Oxygen there can be no rust, however virtually all solid material have some permeability to liquid and gas entrance.

A steel chamber welded shut has very low permeability to these fluids leeching thru, and can be an effective seal IFF there are no cracks or holidays. Paints, and Epoxies have permeabilites allowing far more fluid ingress, but can do a practical job if applied correctly.

Expanding foam has permeability hundreds or thousands of times greater than some epoxies, and these foams might only be good as flotation when exposed to liquids for a few weeks or months, but not for really long term sealing.

 

Ok, to sum up the situation - sealing is not possible, greasing is not possible, epoxying is not possible. This is a structure of a land vehicle, not a boat.

My two cents worth:
Make sure that it is a closed-cell foam, which is the essential requirement. An open-cell foam is the gateway to rust. Do the foam job and live with the fact that it is not an optimum solution, but it is a solution. 7 days have passed since your quest, it's time for action.

Cheers

 

What are you speaking of?

 

speaking of the Parkland's case: http://www.boatdesign.net/forums/bo...nside-steel-pipe-tubing-50666.html#post692457 , which this thread is about.

 

Yup I'm going for it.
The foam spec sheet says it's closed cell, so there we go, I guess.
I'm going to make a longer hose for the foam can dispenser, and I think I should be able to really fill the tubing well.

The product says it bonds to metal, allows flexing, air tight, so sounds like it will work.
This will be nice, The frame will be covered by a thin metal body, so won't get water on it, but the foam is like an extra layer of protection. Maybe it will even reduce the noise of the metal tube framing as well.

I'll post up a few pictures when I do it.
I know it's not a boat, but hey, metal is metal.

 

Well, you have some very good suggestions from people.
Why not incorporate two or more.
Rwatson has a standard method of preventing rust, fish oil. Also, lanoline and kerosene mixture has been used.

Weld a threaded socket at one end, push some 10mm 3/8" reticulation tubing down the pipe with a spray at the end and pump the anti rust solution through the pipe as you draw the pipe backwards.

There are ready made solutions on the market.

Then pump your foam in.

Foam is good anyway as it maintains buoyancy if the pipe leaks.

Seal the socket with a threaded plug and sealant. Done.

Nick, says that fish holds don't rust, could be the fish oil is coming out of the fish onto the steel. Fill the pipe with dead fish

Also the speed of rust, all sorts of structures are made of steel, even with no coating, is the steel going to rust out that fast it will be a problem anyway?

Poida

 

I'm thinking oil could damage the foam maybe.

I can't seal the tubing, some joints can only be welded on 3 sides, and also the body panels are getting riveted onto the tubing, so it will never be air tight unless filled with foam.

 

Is this something you have tried and seen that it works?

I am asking because I have some doubts that foam would adhere to the surface which has been previously coated with an oily anti-rust product.

And one also has to make sure that the foam is chemically compatible and won't melt when in contact with anti-rust chemicals.