Passive flux

[davenport.neil]

Can anyone tell me, is residue from passive flux such as "la-co" corrosive after the soldering process is complete?

Thanks.

 

[Deleted member 25704]

Yes la-co is corrosive, just as all fluxes are. However, it is gas council approved and is suitable for use in the uk for water as well.

It should be used with caution - only flux the male ends, not the fittings, and removed with a damp cloth after soldering. Heating systems should be thoroughly flushed, both hot and cold to get rid of any internal residues.

However, if these conditions were not satisfied, flux on the outside of joints leaves a green unsighlty residue.

On the inside of systems, it an be argued scientifically through sampling and scientific reason, that an increase in the ph of the system water acts as an electrolyte and may lead to electro-chemical corrosion in the prescence of disimilar metals usually found in heating systems. However such occurances would not be down to the flux, but down to occupational quality.

 

[davenport.neil]

Yes la-co is corrosive, just as all fluxes are. However, it is gas council approved and is suitable for use in the uk for water as well.

It should be used with caution - only flux the male ends, not the fittings, and removed with a damp cloth after soldering. Heating systems should be thoroughly flushed, both hot and cold to get rid of any internal residues.

However, if these conditions were not satisfied, flux on the outside of joints leaves a green unsighlty residue.

On the inside of systems, it an be argued scientifically through sampling and scientific reason, that an increase in the ph of the system water acts as an electrolyte and may lead to electro-chemical corrosion in the prescence of disimilar metals usually found in heating systems. However such occurances would not be down to the flux, but down to occupational quality.

Thank you for your response.

So would i be right in thinking that in the case of gas, as some flux residue will find its way inside the pipe due to the fact that the solder is drawn in by capillary action, that it is not a case of if the pipe will corrode from the inside out but just how long it might take?

 

[Deleted member 25704]

I think you could reason this argument that corrosion would go on etc. However, the science which made the product approved, has to be trusted until such times new scientific data is available. I do not know if there is any published data on this issue, but it is an argument which has often been raised in plumbing circles - some plumbers will not use la-co for this reason. However, I do, because there is no scientific argument other than anecdotes to convince me otherwise.

 

[SimonG]

Green pipes, my pet hate. Doen't take a couple of seconds to wipe it down.

I'm not sciency and won't pretend to be, but is corrosion not oxidisation, and as gas doesn't contain oxygen then you shouldn't get oxidisation?

Steps back and waits for the clever lot to put me right!

 

[AWheating]

on wet pipes it gets flushed so dont worry, on gas clean and use very little flux on pipe only. Theres no 100% garantee you will not leave a small amount inside a pipe.

More importantly than what flux is how long. How long the pipe is going to be left de commissioned. If your turning the water on straight away after the work is complete to enable you to flush the pipework then you should have no problems. If your not going to commission for a while, like you would on new builds/ 1st fixes then you must fully flush the pipework straight away bwfore leaving empty. Not flushing can leave contaminates to corrod and bacterial can grow which its dangerous for health reasons. Made even worse by plumbers on new builds using dirty from storage tubs and dirty containers when pressure testing.

obviously on heating systems chemicals can be used to clean and avoid corrosion.

 

[wheeto]

... gas doesn't contain oxygen [so] you shouldn't get oxidisation?

That's exactly what I've always thought but I've never heard anyone else say it before, let alone say it with authority!

 

[lame plumber]

That's exactly what I've always thought but I've never heard anyone else say it before, let alone say it with authority!

contains some water residue tho and thats made of?

 

[Guest123]

My pet hate is seeing snot soldered pipes covered in green flux residues. Shows a lack of skill and care for their work.

As for flux, let the fitting cool naturally (never cool a fitting straight after soldering as capillary action is still taking place) and after about 2 minutes, wipe it over with a baby wipe and the flux is removed and the pipe stays clean.

 

[wheeto]

contains some water residue tho and thats made of?

Oxidation requires free oxygen, and water doesn't spontaneously decompose much. If it did we'd be living in a hydrogen economy (and quite thirsty).