Letter 7046

What is inhibited HCl ? 

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We have a very serious scaling problem in our filter tubes, we have tried all sorts of cleaning mechanisms. we have been informed that inhibited HCl would help in descaling. kindly let us know what inhibited HCl is?

sanghani harshal
- nocil-rcd

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Straight HCl will attack steel as well as scale and rust. Inhibited HCl has organic additives that tend to coat the cleaned steel to inhibit the attack on the steel.


Ted Mooney, P.E. 
finishing.com
Brick, New Jersey

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The word "inhibited HCl" is usually used to indicate hydrochloric acid with acid corrosion inhibitor.

Hydrochloric acid is usually used as diluted in water, particularly 3 to 10% which varies by the fouling characteristics and material in the system.

Acid corrosion inhibitor means organic compound which adsorps metal surface to protect metal from acid atmosphere. It is commercially available and typically composed of several mixture of organic amines, imines, and/or thioureas, and so on.

There are a lot of products from chemical companies in the market and several types depend on the applications such as hydrochloric acid, sulfuric acid, organic acids, and so on.

The inhibited acid is at times heated usually up to 60 deg.C to facilitate the dissolving reaction between scale and the acids.

You should be careful to apply these acids, because hydrochloric acid, even inhibited, could attack some materials, like highly mechanically arranged devices and could lead to serious damage like cracking or partially detrimental corrosion. Especially for austenitic stainless steel, when it is finely modified.

Hiromi Kawaguchi
- Tokyo, Japan

March 6, 2009

i have a project to clean to clean a scaled boiler and also to clean an HVAC network. for the boiler i am going to use the HCL and for the HVAC i am going to use the Citric acid. my question is what is the inhibitor that i can add to the acid and at which concentration? thanks in advance.

charbel Ibrahim
chem engr in water treatment chemicals - Lebanon

July 1, 2009

To make an inhibited HCL solution according to ASTM, add 500ml HCL to 500 ml water, and dissolve in 5g of antimonty trioxide, and 5g of stannous choloride. Ta-da!

Ned Funnell
- Williamsburg, IA

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