caustic soda on a seat post

[rjsdavis]

Re:

Caustic soda is only good for steel and Titanium frames, as it doesn't corrode them. The only issue with a ti frame may be if it has alloy riv nuts for the bottle cages or an alloy insert for the seatpin.
I will be completing my 93 team ti build soon, and I face the issue of a buried seatpost about 6 inches inside the tube, plus it is sat on top of alloy riv nuts, and there is an alloy shim glued inside the top of the seat tube!
A very delicate job in my case.

Just to understand this - when you say that the seatpost is "buried" - do you mean that the whole/part of the seatpin that you are trying to remove is stuck down inside the seat-tube - with no part of it exposed to clamp onto and grip?

Ifso, this is the exact problem that I've got with a Ti frame also. I'd be very grateful to hear how you got on with this?

 

[integerspin]

As far as titanium goes that shouldn't be a problem. It's properties are described as very resistant to sodium hydroxide. A magnet will tell you if the cage bosses are steel or ali, if they are ali it shouldn't be a problem if you don't get the caustic brimming out of the hole and pour it in so it doesn't go on them.

When I took the post out of a steel frame, that had the post cut off and hammered down the seat tube, I took pics while doing it. I stuck a few of the pics on one of the how do i rem a seatpost threads on here.

 

[danson67]

rjsdavis:

Ti is resistant to caustic soda at any concentration, unless you leave it for a veeery long time.
Also no chemical damage unless you try using almost boiling very very alkaline (pH 12+):

"Titanium is very resistant to alkaline media including solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonium hydroxide. Regardless of concentration, titanium generally exhibits corrosion rates of less than or equal to 5 milliinches per year - mpy (0.127 mm/yr). Near nil corrosion rates are exhibited in boiling calcium hydroxide, magnesium hydroxide, and ammonium hydroxide solutions up to saturation. Despite low corrosion rates in alkaline solutions, hydrogen pickup and possible embrittlement of titanium can occur at temperatures above 170°F (77°C) when solution pH is greater than or equal to 12. Successful application can be achieved where this guideline is observed."

https://www.azom.com/article.aspx?ArticleID=1239

All the best,

 

[The History Man]

Tame the beast..........

It’s great fun too!

 

[rjsdavis]

rjsdavis:

Ti is resistant to caustic soda at any concentration, unless you leave it for a veeery long time.
Also no chemical damage unless you try using almost boiling very very alkaline (pH 12+):

"Titanium is very resistant to alkaline media including solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonium hydroxide. Regardless of concentration, titanium generally exhibits corrosion rates of less than or equal to 5 milliinches per year - mpy (0.127 mm/yr). Near nil corrosion rates are exhibited in boiling calcium hydroxide, magnesium hydroxide, and ammonium hydroxide solutions up to saturation. Despite low corrosion rates in alkaline solutions, hydrogen pickup and possible embrittlement of titanium can occur at temperatures above 170°F (77°C) when solution pH is greater than or equal to 12. Successful application can be achieved where this guideline is observed."

https://www.azom.com/article.aspx?ArticleID=1239

All the best,

Thanks for this Danson - appreciated.

I'll be removing the press-fit B/B, so it's just a bare frame, but I've got a concern that seat-tube bottle boss eyelets are ally, and hence would be melted by the hydroxide solution. The rammed in seatpost remains are pretty damn near, if not covering, the top bottle boss from the inside.... therefore, trying to work out how best to leave a quantity of solution in the seat-tube working on the seatpost remains for a period of time, but without affecting the bottle boss/es.

I can leave the frame "headtube up" in the workstand, and squirt some solution in with a syringe or something from the seat-tube / seatpin opening, which would work a bit on the section of seatpin that's resting against the back 1/4 edge of the seat-tube. I would imagine that once this has been eaten away, the seatpin remnants will pry up more easily away from the seat-tube itself and become emanantly more workable to remove?

 

[danson67]

Re:

I'd leave the bottle bosses in and see what happens.
They're probably zinc plated steel, rather than alu.
If they are alu and get damaged by the caustic, they can be drilled out with a 7.5mm drill and simply replaced. I have the kit if you need.

All the best,

 

[Bawgixer]

Re:

I did it few weeks back to a Karakoram frame,the post was stuck down inside the frame as previous owner had trying sawing and holding it in a vice.
Frame was turned up side down and placed in a plastic storage box.
The bb was removed and a funnel and fuel line hose was used to put the caustic down through the bb into the seat tube,the seat tube was sealed off using and old inner tube cut and slide over the opening then folded over n over a few times then cable tie to hold shut,the bottle bolts were removed and again inner wrapped round to seal.
When the caustic was put in and the reaction started I ran cold water down the out side of the frame to limit the heat transfer effects on the paint surface.
£10 of caustic from local hardware store was used and It took Near 2 hrs for it to be clear.

 

[rjsdavis]

Re: Re:

I'd leave the bottle bosses in and see what happens.
They're probably zinc plated steel, rather than alu.
If they are alu and get damaged by the caustic, they can be drilled out with a 7.5mm drill and simply replaced. I have the kit if you need.

All the best,

Thanks for this Danson.

I definitely don't want to get into the situation of having to drill out and replace the bottle bosses! I'd rather leave the remnants where they are than do this - particularly on a frame like this.

I've now got the press-fit bottom bracket out, and I've been looking over the frame really carefully, and I think I've got some additional complicating factors:

1 - The bottom bracket shell appears to have an ally sleeve in it, that the press-fit parts butt up against. It's defo not magnetic, so assuming that it's not any sort of steel. My concern about this, is that any caustic just tipped into the seat-tube will eat into and through this from the bottom of the seat-tube! If the frame was upright.

2 - I can now see that the top of the seat-tube has an internal sleeve, approximately 20cm long from the very top of the seat-tube. Again, I am assuming that this is also ally. Therefore, if the frame was upside down and caustic tipped in by say one of the bottle bosses, this sleeve would be damaged / eaten by the caustic also! It is not possible to get to the seat-tube, via the bottom bracket, because of the bottom bracket sleeve mentioned above.

3 - The bottle bosses themselves appear to be ally. They are not magnetic at all, therefore concerned that these would be damaged in the process if caustic was allowed to sit in the tube

Troubled now, and struggling to come up with a removal plan!

 

[Weon]

Re:

I know it's not the whole "doing it yourself" vibe, but this guy is awesome - he's removed a post for me and left the frame lovely and smooth inside. Saved me a load of hassle.

http://theseatpostman.com/

(and no, I'm not on commission!)

 

[danson67]

Re:

I'd point you in the direction of the seatpost man, too, given the complications you have.

£70 or so well spent.

All the best,