How to descale chrome components without damage?

Need help with equipment usage or want to share your latest discovery?
skydragondave

#1: Post by skydragondave » Mar 03, 2013, 8:20 pm

Hi all, wondering if you can help me.
I've been carefully descaling the group head on a commercial machine. It's been very tedious filling the passages with diluted acid, warming the group head up, rewarming it, and so on until scale is cleared. I have several more to descale. How do you guys do it?
I've noticed the acid mix will only fizz when it's warm. All activity seems to stop once it gets cold. I've heard mention of using a 100-cup coffee urn to acid-dip parts in, which would be great except in the case of a chromed group head or nickel-plated boiler. How does one handle this?
I just purchased a 5G stainless stock pot for dipping, that I plan on warming with a hotplate. What temperature should I be aiming for to descale parts with?
Thanks for any advice.
LMWDP #433

kboom1

#2: Post by kboom1 » Mar 04, 2013, 9:56 am

what type acid or descaling solution are you using? I've had issues in the past using different descaling products that will scar stainless and chrome but never had a problem with a citric acid solution mixed properly.

User avatar
rpavlis

#3: Post by rpavlis » Mar 04, 2013, 12:52 pm

You should not consider using any acids other than acetic or citric. If you having things disassembled, you should really only use vinegar. Acetic acid is a weaker acid than citric, and calcium acetate is soluble. Under some conditions you can get citric acid to precipitate insoluble calcium citrate in place of the calcium carbonate. It is also easier to use acetic acid, you simply buy a jug of white vinegar. It can be diluted a bit with water if desired. Warming to just a bit above room temperature, say 35-45C should be fine.

You must take great care to get rid of either acid after doing this, especially with vinegar. The vapour pressure of acetic acid is substantial, so relatively small residues can make "espresso salad" if one fail to remove every last trace of it by thorough rinsing.

Hydrochloric acid is a particularly bad idea with either brass or copper. It forms complexes with copper and other metals, and CuCl is stable and small amounts of it in pores in the metal can initiate what is called "bronze disease."

User avatar
erics

#4: Post by erics » Mar 04, 2013, 1:45 pm

I've been carefully descaling the group head on a commercial machine.
It would be helpful, perhaps, if you identify the victim.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

skydragondave

#5: Post by skydragondave » Mar 04, 2013, 6:25 pm

Hi Eric,
I've been careful to avoid identifying the "victim" (Ouch! I haven't killed it yet!) because I don't want product-specific answers here, I am seeking general shop practices guidelines to apply to all the machines I work on.
I've been using a liquid phosphoric acid descaler manufactured by a local company (it's not sold in the US) which has mixing directions for use in coffee urns. I've been using a higher concentration because it does nothing to the heavy scale I've been finding at the recommended concentration.
I've been using the liquid because at the time I bought it, I was told that citric acid powder is best for maintenance-level descaling where no disassembly is required, and for heavy scale I needed something more aggressive. Since then I've seen Doug at OE using citric acid exclusively to tackle in some cases some pretty heavy scale in the many videos he and Barb have posted, so I'm starting to question my decision. If "bronze disease" or any other ill effects are caused by using phosphoric acid, I'll definitely stop using it, but I'd like to know more about it if any of you care to humour me.
In any case I want to avoid immersing chrome or plated parts to avoid damaging them. I'm just not sure what else to do with them. I upended the group head casting and filled the warming passages with diluted acid, and immersed that in a small bucket of hot water, changing the water when it got cold, and that seemed to go okay. I'm now descaling a vertical passage near the back, resting the grouphead upright and running hot water through the warming passage with a hose to keep it warm, but it's pretty tedious having to babysit one part for a whole evening. There has to be a better way!
Thanks again for reading and any help you can offer. Cheers
LMWDP #433

User avatar
Paul_Pratt

#6: Post by Paul_Pratt » Mar 04, 2013, 9:53 pm

To descale without any risk of removing chrome you need to leave the machine intact and then get the citric into the boiler and the HX's. If you can, get the steam boiler level higher than normal. Leave the machine at operating temp for a few days, occasionally letting off steam, pulling hot water and pulling a shot or two to get the water moving around. Drain, inspect and repeat as necessary. I would always strip the machine and rinse again after this to be sure that I have removed all the grains of scale.

This would help clean the group internals, after all that you should probably do a regular soak type descale of all the other bits like boilers, pipes etc..

Not the best way to descale a machine but it will not touch the chrome.

You can always put the chrome bits in citric and hot water and keep an eye on them and remove them from time to time to make sure the chrome is still good. I do this all the time without any damage to the finish.