Brazing Pickle

Edited By mgj on 06/04/2010 22:40:11

Thanks for the comments. I ought to point out that although I had many years experience in chemical cleaning of industrial plant, I have never silver soldered or made a brazed joint in my life – I have all that good fun stuff to look forward to – so I don’t have any real experience of removing fluxes and general cleaning up after hot work.

My points are pretty general. As you say, all we are trying to do is to remove a ‘scale’ and leave the base material unharmed. Unfortunately, all the common acids used for metal cleaning WILL attack the base metals, it’s just in their nature to do it! Slight qualifier here – copper, some grades of stainless steel and some fairly exotic high nickel content alloys such as R55 probably won’t be attacked but normal carbon steels, aluminium and zinc containing alloys will be chewed at by the acids. In fact even pure water will attack steel like an acid (i.e dissolve the metal and liberate hydrogen) if the temperature is high enough.

So, don’t underestimate that bit of lemon juice, it can, does and will happily dissolve steel. Just takes a long time to do it so the effects aren’t obvious. For what it’s worth the order of ‘aggressiveness’ on carbon steel is something like:

Hydrochloric, Sulphuric

Phosphoric acid

Citric acid

Hydrofluoric acid – NB Do not try this one at home!!

Then there are various descalers that work in alkaline conditions that are based on chelating agents such as EDTA. Very safe but need to be used very hot and are not easy to get hold of anyway. Caustic soda (Sodium hydroxide) is fairly good for general cleaning but nasty to handle.