Hullo Nige, hope you're still letting the good times roll 
Nige I was avoiding HCl because it's not good for stainless steel.
In case it's of interest to anyone, FX2 did the business. The data sheet says it has >34% Phosphoric Acid and some Citric Acid. I put 1.25 litres of FX2 into 5 litres of water, and there was about 1 litre of plain water (left over from flushing) still in the coil, so I reckon the net concentration was about 7% Phosphoric. I also like the fact that it's a liquid, so no powder to have to dissolve and dust to have to avoid inhaling.
After 24 hours of this solution, at about 70 deg C, the flow rate through the coil more than doubled, so now it's usable again and I have one customer who's happy not to be needing a new cylinder.
Thanks to everyone for their advice.
Oh - one more thing; I found a supplier of Nitric Acid and completed their obligatory declaration form so that I can order it, just in case it was needed. I haven't noticed any police helicopters overhead, but I'm not wearing my backpack anymore....
Nige I was avoiding HCl because it's not good for stainless steel.
In case it's of interest to anyone, FX2 did the business. The data sheet says it has >34% Phosphoric Acid and some Citric Acid. I put 1.25 litres of FX2 into 5 litres of water, and there was about 1 litre of plain water (left over from flushing) still in the coil, so I reckon the net concentration was about 7% Phosphoric. I also like the fact that it's a liquid, so no powder to have to dissolve and dust to have to avoid inhaling.
After 24 hours of this solution, at about 70 deg C, the flow rate through the coil more than doubled, so now it's usable again and I have one customer who's happy not to be needing a new cylinder.
Thanks to everyone for their advice.
Oh - one more thing; I found a supplier of Nitric Acid and completed their obligatory declaration form so that I can order it, just in case it was needed. I haven't noticed any police helicopters overhead, but I'm not wearing my backpack anymore....
