Acid cleaning limescale 3

[StephenA]

We have a pipeline with a thick layer of limescale (up to 15mm). Some of it can be scrapped off but we are thinking to use Citric acid to clean the bends, delivered between a pair of pigs.

The question is how much acid do we need and how long do we leave it in place?

StephenA

 

[bimr]

The answer depends on many factors such as what the pipeline is used for, what has caused the scale, the size and length of the pipeline, and the material of construction of the pipeline.

Why have you focused on citric acid? Have seen others use hydrochloric, but not citric.

http://www.pubs.asce.org/

http://WWWdisplay.cgi?9402488

http://www.new-technologies.org/ECT/Other/pipechem.htm

 

[cub3bead]

Citric has three carboxlyic acid groups (i.e. 3 replaceable H atoms).

You should be able to estimate the mass of the scale fairly accurately. Do you know if it is Ca(OH)2 or CaCO3? If CaCO3 the CO2 will form bicarbonate and buffer the acid base neutralization and require more acid. (pKa = 3.13, 4.76, 6.40.)

I would recommend that you contact a chemical cleaning contractor and talk to them about this.

PS - dilute HCl maybe faster and cheaper to do this cleaning with

 

[StephenA]

Thank you for your replies.

The line is an effluent line discharging to the sea. The limescale (96% CACO3) is up to 15mm thick and coating 50% of the circumference.

The citric acid has been recommended as being more environmentally friendly.

We can easily calculate the mass of the scale, and were wanting to find out the quantity of acid required per kilogramme of limescale.

 

[m777182]

A friend of mine made big money by removing lime scale deposits in potable water pipings in hotels.He simply used HCl with some EDTA and was following Zn concentration in the effluent potentiometricaly. He stopped the flow when he detected Zn.
m777182

 

[kenvlach]

Since discharging to the ocean, hydrochloric acid would be more environmentally friendly than citric -- the HCl rxn. with scale makes saltwater.

It might be difficult keeping the citic acid solution hot to keep it effective. Also a slight(!!!) problem that calcium citrate [CAS# 813-94-5, Tricalcium Dicitrate Tetrahydrate] is almost insoluble in water. Of course, it is ~non-toxic (permitted in food), so you could eat it.

I suggest using dilute HCl (don't want localized heating or pipe corrosion) and monitoring the pH of the effluent to control your pumping speed. Not sure how well pigging will work with changing ID as scale dissolves, but if pigging, make several fast passes, don't try do do in one.

When the scale gets thin, add sodium silicate to the HCl solution to inhibit attack on the pipe in the clean areas.

 

[unclesyd]

You might want to look at this material. It is an excellent cleaner for lime scale. It is based on HCl and has all the inhibitors, surfactants, rinse agents needed.

http://www.rydlyme.com/home.html