Inhibitors for Citric Acid descaling solution 1

[moltenmetal]

What sort of inhibitor is used in citric acid descaling solutions? I've seen commercial inhibitor brand names mentioned but want to understand what class of chemicals these are and how they work to inhibit parent metal corrosion.

 

[EdStainless]

It will depend on the metals involved.
You aren't going to remove much scale with citric unless you are concentrated and hot.
Citric makes a good SS pasivation treatment.

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Plymouth Tube

 

[moltenmetal]

Yes, Edstainless, it's a highly technical question this time!

It's hot, but not that concentrated- but effective, and shockingly expensive I might add, though not quite giving ink jet printer ink a run for its money...Used every few months in my espresso machine!

The boiler on my espresso machine is apparently stainless steel (grade unknown).

The vendor doesn't give out MSDSs for their de-scaling solutions, and the "caution" list includes citric and lactic acids and "corrosion inhibitor". I'm curious what strategy you would use to inhibit parent metal corrosion against an organic acid like this. Obviously you flush the system really well after use, but I'm still curious what's in there and how it works.

 

[stanweld]

It appears that you are descaling calcium carbonate deposited on the ID surface. If so, I have found that vinegar does a fine job of scale removal.

 

[moltenmetal]

Yes, that's normally the 1st thing I'd reach for, but the manufacturer recommends specifically against vinegar in their manual for some reason (possibly to sell more expensive de-scaling solution!). And I paid enough for the machine that I'm not inclined to ignore that advice...

Yep, it'd be a calcium/magnesium carbonate/sulphate and iron scale on the ID of the boiler. They give no explosion drawing and I've never had the machine apart to know what it looks like. The alkalinity here is relatively low, but insufficiently frequent de-scaling is the death of these machines for sure.

 

[unclesyd]

Check the local grocery store for CLR. If not there check the big box stores, either blue or orange.

 

[moltenmetal]

Unclesyd: never would have even considered dumping that stuff into my snooty little espresso machine, but since you suggested it, I took a look at the MSDS for CLR. I'd always figured it to be a sulphamic acid or HCl concoction, but no- it's lactic acid, a lauric acid surfactant (presumably as a metal coating inhibitor?) and a "cellosolve" type glycol ether (hmm, not sure what that's for- just to thicken it a bit?). Guess that IS actually a direct and cheap replacement for what the espresso manufacturer sells!

A well deserved star, again- you're a great resource!