I was helping out a chap that collects military vehicles from the 70s. A
coolant reservoir had developed a pin prick rust hole fairly near a
seam. Initial inspection made me think it was basically a steel
cylinder construction tinned after the joints and pipes had been
attached. The tinning had corroded to allow some light rusting over the
surface.

I chose to braze the hole shut. The interesting thing, to me was the
adjacent joint was some sort of hard solder. It would have been far
tooexpensive to be silver solder. Anyway I sealed the hole and the
adjacent solder melted a bit but no damage.

I now need to address the surface rusting and was thinking of using
hydrochloric acid and then wondering about re tinning, any suggestions
for what to use? On another rusty tank I previously used zinc chloride
flux and an old lead based solder, a heat gun and wiped it on but it
was a bit patchy.

On 08/05/2021 13:20, AJH wrote:
I was helping out a chap that collects military vehicles from the 70s. A
coolant reservoir had developed a pin prick rust hole fairly near a
seam. Initial inspectionÂ* made me think it was basically a steel
cylinder construction tinned after the joints and pipes had been
attached. The tinning had corroded to allow some light rusting over the
surface.

I chose to braze the hole shut. The interesting thing, to me was the
adjacent joint was some sort of hard solder. It would have been far
tooexpensive to be silver solder. Anyway I sealed the hole and the
adjacent solder melted a bit but no damage.

I now need to address the surface rusting and was thinking of using
hydrochloric acid and then wondering about re tinning, any suggestions
for what to use? On another rusty tank IÂ* previously used zinc chloride
flux and an old lead based solder, a heat gunÂ* and wiped it on but it
was a bit patchy.

My first port of call would be plumbers flux. Though I guess they're not
all equal.

I recall an instance when I attached a copper pipe to a club hammer I
was using to support the pipe whilst soldering a joint.

On 08/05/2021 13:20, AJH wrote:
I was helping out a chap that collects military vehicles from the 70s. A
coolant reservoir had developed a pin prick rust hole fairly near a
seam. Initial inspectionÂ* made me think it was basically a steel
cylinder construction tinned after the joints and pipes had been
attached. The tinning had corroded to allow some light rusting over the
surface.

I chose to braze the hole shut. The interesting thing, to me was the
adjacent joint was some sort of hard solder. It would have been far
tooexpensive to be silver solder. Anyway I sealed the hole and the
adjacent solder melted a bit but no damage.

I now need to address the surface rusting and was thinking of using
hydrochloric acid and then wondering about re tinning, any suggestions
for what to use? On another rusty tank IÂ* previously used zinc chloride
flux and an old lead based solder, a heat gunÂ* and wiped it on but it
was a bit patchy.

Personally, I'd be tempted to use a gas torch and an active flux.

On Saturday, 8 May 2021 at 20:32:06 UTC+1, newshound wrote:
On 08/05/2021 13:20, AJH wrote:
I was helping out a chap that collects military vehicles from the 70s. A
coolant reservoir had developed a pin prick rust hole fairly near a
seam. Initial inspection made me think it was basically a steel
cylinder construction tinned after the joints and pipes had been
attached. The tinning had corroded to allow some light rusting over the
surface.

I chose to braze the hole shut. The interesting thing, to me was the
adjacent joint was some sort of hard solder. It would have been far
tooexpensive to be silver solder. Anyway I sealed the hole and the
adjacent solder melted a bit but no damage.

I now need to address the surface rusting and was thinking of using
hydrochloric acid and then wondering about re tinning, any suggestions
for what to use? On another rusty tank I previously used zinc chloride
flux and an old lead based solder, a heat gun and wiped it on but it
was a bit patchy.
Personally, I'd be tempted to use a gas torch and an active flux.

Phosphoric acid is good.

John

On 09/05/2021 11:43, John Walliker wrote:
Phosphoric acid is good.

I've got some 80% strength what dilution? Why would it be better than
hydrochloric acid?

I am thinking of unearthing a set of bodywork books from the 1930s that
my wife's granddad gave me shortly before he died in the 60s. He was an
old school pane beater and before resin fillers they would beat out the
dents and use lead to get the final finish as a skim.

On 09/05/2021 13:29, AJH wrote:
On 09/05/2021 11:43, John Walliker wrote:
Phosphoric acid is good.

I've got some 80% strength what dilution? Why would it be better than
hydrochloric acid?

I am thinking of unearthing a set of bodywork books from the 1930s that
my wife's granddad gave me shortly before he died in the 60s. He was an
old school pane beater and before resin fillers they would beat out the
dents and use lead to get the final finish as a skim.

Phosphoric will convert the oxide (rust) to an adherent layer of iron
phosphate. Good if you are going to paint, less helpful if you wanted to
tin. Hydrochloric if you want to pre-treat (active fluxes are doing the
same thing).

On Monday, 10 May 2021 at 21:42:03 UTC+1, newshound wrote:
On 09/05/2021 13:29, AJH wrote:
On 09/05/2021 11:43, John Walliker wrote:
Phosphoric acid is good.

I've got some 80% strength what dilution? Why would it be better than
hydrochloric acid?

I am thinking of unearthing a set of bodywork books from the 1930s that
my wife's granddad gave me shortly before he died in the 60s. He was an
old school pane beater and before resin fillers they would beat out the
dents and use lead to get the final finish as a skim.
Phosphoric will convert the oxide (rust) to an adherent layer of iron
phosphate. Good if you are going to paint, less helpful if you wanted to
tin. Hydrochloric if you want to pre-treat (active fluxes are doing the
same thing).

I have used concentrated phosphoric acid as a flux when soldering stainless
steel. It can spit a bit, so wear eye protection. It makes really nice joints with
tin/lead solder. I haven't tried lead-free solder.
Hydrochloric acid or chlorine containing salts are more likely to leave corrosive
residues as chloride ions catalyse rusting.

On 11/05/2021 12:41, John Walliker wrote:
On Monday, 10 May 2021 at 21:42:03 UTC+1, newshound wrote:
On 09/05/2021 13:29, AJH wrote:
On 09/05/2021 11:43, John Walliker wrote:
Phosphoric acid is good.

I've got some 80% strength what dilution? Why would it be better than
hydrochloric acid?

I am thinking of unearthing a set of bodywork books from the 1930s that
my wife's granddad gave me shortly before he died in the 60s. He was an
old school pane beater and before resin fillers they would beat out the
dents and use lead to get the final finish as a skim.
Phosphoric will convert the oxide (rust) to an adherent layer of iron
phosphate. Good if you are going to paint, less helpful if you wanted to
tin. Hydrochloric if you want to pre-treat (active fluxes are doing the
same thing).

I have used concentrated phosphoric acid as a flux when soldering stainless
steel. It can spit a bit, so wear eye protection. It makes really nice joints with
tin/lead solder. I haven't tried lead-free solder.
Hydrochloric acid or chlorine containing salts are more likely to leave corrosive
residues as chloride ions catalyse rusting.


Isn't that what 'Kurust' was intended for ?. That has been
reformulated as a water-based compound and is nowhere near as
good as the original product.