Chrome friendly descalers?

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BaristaMcBob

#1: Post by BaristaMcBob »

Urnex Descaler definitely eats chrome. What about their phosphate-free product, Biocaf Descaler? Does anyone have experience with it?
Any other products worth considering? This would be for descaling an HX. I'm worried about descaler coming in contact with chrome parts on the machine's exterior (e.g., hot water tap).

Sw1ssdude

#2: Post by Sw1ssdude »

Sulfonic (sulphonic?) acid. Found in DURGOL brand descalers. is very gentle, but also very effective. also good for the questionable alloys in (gasp!) Bialetti coffee makers.

Citric acid has not (yet) eaten the chrome off my machines, but definitely eats away Nickel and Copper. it also dissolves the black copper oxide, so thorough rinsing is a must (might be difficult with a HX).

Vinegar is also cheap and easy to use. but it will eat all kinds of metal.

I'd say all three can be used on chrome. as long as you're not soaking these parts over night, it will be no problem. like flushing through the hot water tap or the group will be wayy too little time for the acids to eat away your chrome. just rinse with plenty of tap water, and all will be well...
Lean Mean Caffeine Machine

WWWired

#3: Post by WWWired »

Hi BaristaMcBob :)

As Sw1ssdude mentions, the more likely metal to be affected by descalers will be Copper or Nickel and if a descaler can get beneath Chrome plating (through a crack etc.) it might attack the base metal depending on what it is (copper etc.).

Descaling of Chrome plating and other metals may expose already present underlying galvanic and other corrosions. Corroded metals can be vulnerable during descaling with a corrosive agent (Acetic, Sulfonic, Citric Acids for example). With many of these Weak Acids, the corrosive effect is primarily subject to duration of exposure and temperature, but also is subject to the anodic index difference of the two metals involved. Any signs of corrosion should be addressed, and use of a descaler will often expose any hidden corrosion that may be occurring - a good thing as it allows the corrosion to be identified and addressed so ingestion of metals can be avoided.

An approximately 3% Citric Acid Solution might involve 1 or 2 tablespoons of Citric Acid (available in bags cheaply from any Home Brew or Wine Making Supply Shop) per 1 Liter (quart) of water. Most Vinegars (Acetic Acid) are usually about 5% solution of Acetic Acid in water, but may leave a flavour/odor residue unlike other descalers.

Resistance of Hard Chrome Plating to a 10% solution of Citric Acid in water (100 grams per liter, or about 7 Tablespoons per Quart) is considered to be:
  1. "Excellent" at 55℉ (13℃)
  2. "Moderate" at 135℉ (57℃)
This would seem to indicate that at about 55℉ (13℃) that Chrome plating is fairly resistant to normal descale solutions. If any signs of corrosion are being exhibited, this is likely due to previous damage that is just becoming evident due to the use of the descale solution, not because of it.

Corrosion underlying the flaking/damaging of Chrome could depend on the anodic index difference between the plating material and the base material/metal. A difference of 0.25 V between two metals may result in the more negative metal experiencing galvanic corrosion . . . this may present as pitting, flaking and what may be interpreted as dissolving of the chrome plating but may in fact just be the underlying base metal or Chromium plating showing the results of corrosion that may have been occurring well before the descaling. For that reason, Descaling should be seen as a good chance to assess the state of any possible corrosion occurring to metals inside the machine.
Anodic Index of Chrome Plating to Metals Commonly Found in Espresso Machines:
METAL..................INDEX (V)
Chromium.......-0.50 (18% CRES Corrosion-Resistant-Steel)
Chromium.......-0.60 (Plated, 12% Chromium-type CRES)
Copper............-0.35
Brass...............-0.40 to -0.45
Nickel..............-0.30 (Solid or plated)
Aluminum.......-0.75 (2000 Series Wrought aluminum)
Aluminum.......-0.90 to -0.95 (Wrought alloys or cast alloys, plated and chromate)

Based on the above anodic index numbers, it would appear that most of the metals used in high quality espresso machines should exhibit a reasonable level of resistance to galvanic corrosion since the anodic index differences are largely within the 0.25V range.

It is possible that any damage to chrome plating may be occurring due to already present corrosion that has occurred between the base metal and plating metal and a descaler may just be cleaning up the already existing issue or revealing it. This is likely a good thing as ingesting certain types of metal ions may pose a health risk. Chromium(III) ions are considered important to health, however Chromium(VI) is considered to have some Toxicity and carcinogenic concerns. Chrome platings may involve Chromium(VI) and any signs of corrosion should be addressed to avoid ingestion of metals.

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JohnB.
Supporter ♡

#4: Post by JohnB. »

Sw1ssdude wrote:
Vinegar is also cheap and easy to use. but it will eat all kinds of metal.

I'd say all three can be used on chrome. as long as you're not soaking these parts over night, it will be no problem. like flushing through the hot water tap or the group will be wayy too little time for the acids to eat away your chrome. just rinse with plenty of tap water, and all will be well...
I use cold undiluted white vinegar exclusively for descaling parts & have never had it eat into or dissolve any of the metal (steel, brass, copper). This includes leaving parts soaking overnight or longer. As for attacking chrome I once left several old LM chrome plated pfs soaking in a tub of white vinegar for 10 days hoping it might strip the chrome & it did absolutely nothing. The pfs had deep scratches through the chrome layer yet the vinegar had no effect other then cleaning the chrome.
LMWDP 267

BaristaMcBob (original poster)

#5: Post by BaristaMcBob (original poster) »

Thank you for the info. You mentioned a 3% citric acid solution. Why not add more powder - make it a 6% or 9% solution. Wouldn't that descale faster or more effectively? I realize that might be a naive question.

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homeburrero
Team HB

#6: Post by homeburrero »

BaristaMcBob wrote:You mentioned a 3% citric acid solution. Why not add more powder - make it a 6% or 9% solution. Wouldn't that descale faster or more effectively? I realize that might be a naive question.
Perfecly reasonable question.

A 6% solution (60 g or about 4 tablespoons of citric acid per liter) would work faster and dissolve twice as much limescale. But it would also be much more acidic and potentially corrosive.

A 6% solution of citric is comparable to full strength white vinegar in terms of how much limescale it can dissolve. But where the white vinegar (5% acetic) pH is around 2.4, the 6% citric would have a pH closer to 1.6. Since pH is a log scale that's a big difference - about 6x higher concentration of [H+] ion. Sticking with 3% or less is prudent, although if you have a lot of scale to dissolve you may need to repeat with a fresh acid solution.
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

BaristaMcBob (original poster)

#7: Post by BaristaMcBob (original poster) »

I see. Thank you for the explanation. So, if I have a lot of limescale, sounds like it's better to repeat the process with 3% acid than to try a single treatment with 6%.

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homeburrero
Team HB

#8: Post by homeburrero »

BaristaMcBob wrote:So, if I have a lot of limescale, sounds like it's better to repeat the process with 3% acid than to try a single treatment with 6%.
Yes. Even at 3% (about two tablespoons per liter) it would have a lower (i.e., more acidic) initial pH than pure white vinegar. For routine descaling with very little scale in the machine you could go even lower than 3%. Doug Garrott at Orphan Espresso used to recommend mixing up a 1 tablespoon per liter solution. Dr Pavlis preferred white vinegar, and sometimes diluted to half strength for small boiler descaling. (Vinegar has an advantage over citric in that it would not create a calcium citrate precipitate. It also requires a thorough flushing to get rid of the vinegar smell, which can aslo be viewed as an advantage because that forces you to rinse fully. )
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

BaristaMcBob (original poster)

#9: Post by BaristaMcBob (original poster) »

I noticed that one of the differences between Urnex Dezcal and Urnex Bio Caf is that the latter does not contain a flocculant (aluminum sulfate). I wonder if Bio Caf would also not produce a precipate, like vinegar.