Hydrochloric acid (brick cleaner) to clean s/s props?

[CaptainMike1970]

I saw a recent thread on here about cleaning S/S props with hydrochloric acid (brick cleaner) and as this is a job on the to-do-list for the weekend I bought 5 litres of the stuff from Jewson (plus all the correct PPE).


However it clearly states on the back of the container DO NOT USE ON STAINLESS STEEL plus a quick “google” brings up

“Hydrochloric Acid: All concentrations of hydrochloric acid will attack stainless steels because the acid destroys the passivity”

The internet did however suggest that the use of nitric or sulphuric acid would be OK.

It also suggested that hydrochloric acid would make the S/S brittle – not very good for a propeller!

Any thoughts, experiences or scientific explanations would be much appreciated.

 

[duncan]

whilst I think nitric is used to clean ss in welding for the reasons you give the principle here seems more around a quick clean inc calcium deposits and other plant material.

 

[sealine]

Hi

What they say is right, stainless steel is passivated in 50% nitric acid for 30 minutes, this removes all the impurities inbedded by the machining process, (tooling) from the stainless (which is the route cause of SS rusting) the SS is then placed in solution of copper sulphate for 3 minutes, should the ss have a fine copper coating, impurities are still in the SS, so the process is repeated until no traces of copper are detected, the SS is then classified as passivated. By placing the props in HCL for a long piriod it removes the film and can cause the SS to become brittle. But if brushed on for a minute or two at the most should have no effect, you will notice the acid will start to fizz within seconds and cleans very fast, so only needs to be on the props for less than a minute, then wash off with plenty of water.

 

[wilsibabes]

I would use one of the pickling acids available at good welding suppliers. These are designed to remove the oxidation left after welding and some pickling agents can clean and leave a protective oxidation layer.
You must only use a stainless wire brush to avoid cross contamination and try to avoid using any carbon steel tools whilst cleaning the stainless.

 

[eyehavit]

While there seems to be plenty who from their own experience advocate cleaning stainless steel with HCl, (aka hydrochloric acid aka spirits of salts aka muriatic acid), it is not good practice.
Try a 10~15% concentration by weight of ordinary citric acid powder dissolved in warm water. Its effective and non-toxic. Do wear safety goggles and elbow length rubber gloves because if citric acid splashes into eyes or a cut it will really sting.
Citric acid does not interfere with the oxide surface of stainless steel.
We buy it in bulk from any of the food processing wholesale people but I reckon any decent grocery store will sell small packs.

 

[thefatlady]

Stainless steel is only "stainless" by virtue of a molecular layer of chromium oxide on the surface. Hydrochloric acid destroys this layer and the steel will then rust. It should do no other harm.

It is for this reason that hydrochloric acid is used in stainless steel soldering flux.

If the suface of the steel is subsequently abraded to expose a new surface, the chromium oxide layer will re-form.

 

[capnjack]

This is exactly how I thought SS is structured. It is classed as a self repairing material, which is why it is so popular.

I don't understand how it can become brittle, unless it is a very thin coat, or has a high Chromium level, as in for example Surgical Stainless Steel.

Perhaps the experts can provide a little more explanation please.

 

[DAKA]

Brick cleaner works fine and contains something to help protect metal.
You are not going to submerge them in solution so what actually happens is


as you pour the acid on the alkaline growth immediately neutralises the acid , leaving on for 30 mins before a rinse off is not a good idea but you are not leaving acid on for 30 mins just an almost ph neutral used mush.

like everything dont over do it, splash it on wait 5 mins and rinse off with fresh water or alkaline salt water even better !

Any missed bit treat with a brush and dont be tempted to pour a load more on as once the alkaline growth has gone the acid will remain stronger.

I left some very thin ss line cutters submerged for a day and they were wrecked, they were only 1 or 2 mm thick.

 

[Deleted User YDKXO]

Using hydrochloric acid on props is very common in the Med because of the agressive fouling but only on bronze props. I don't think anyone on this forum has recommended using HCL on stainless steel

 

[cliff]

Strong acid solutions (e.g. hydrochloric acid or "spirits of salts") are sometimes used to clean masonry and tiling of buildings but they should never be permitted to come into contact with metals, including stainless steel. If this should happen the acid solution must be removed immediately by copious water flushing.

Any HCl based product will create corrosion stress cracking in stainless steel over time, also known as hydrogen embrittlement.

Acetic acid can be used to remove lime scale deposits (25% soln)

Nitric acid is also good if you can get it (25% soln and no hotter than 40°C) - do be careful of the fumes!

If you do use HCl you are asking for problems.

Why do you want to acid wash the props anyway?, what is the contaminant you are trying to get rid off?
--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[CaptainMike1970]

Many thanks for some great advise.

 

[CaptainMike1970]

Well the job is done and the HCL stayed in the bottle, the solution was much closed to home, less risky and much easier than I thought.
1) Make sure SWMBO is out of the house
2) Pop the props in the dishwasher with two dishwasher descaler tablets and set it off on a full power wash
3) Return an hour or so later a remove very nearly spotless props.
4) Spary with Alloy Wheel Cleaner (£3.49 from Halford) and scrub the really stuck on stuff with a nylon pan scrub
5) Rinse in fresh water
6) Get props and all evidence back to garage before SWMBO returns home, bribe Shipmate Nr 1 with smarties and biscuits not to grass me up to SWMBO
7) JOB DONE, props look like new.

 

[tcm]

oh hell

sheet! I think other people should be warned of the incredible dangers and even the sheer stupidity of using a dishwasher like that. For a start, if you get found out it shows that you know where the dishwasher actually is, and how it works...