Sulphuric Acids in Steel industries for picling

“Picking is immersion of objects in dilute acid for the purpose of removing
oxides orscale. The most common acids used for pickling is hydrochloric acid, Sulphuric acid and Phosphoric acid”.

Hydrochloric acid, being fuming in nature, is normally used at room temperature unheated), while both Sulphuric and phosphoric acid are used, both heated and unheated.


SULPHURIC ACID PICKLING BATH
BATH MAKEUP

20-25Litres / 100litres of water.

CONTROL POINTS
Strength 20-25- Check daily
Iron Content (Fe) 10% Max – Check weekly.

TEST METHOD ( For both Hydrochloric Acid & Sulphuric Acid baths )

STRENGTH
1.Pipette 10 ml of bath solution in to a 100ml measuring Cylinder. Dilute to 100ml
Distilled water.
2.Pipette 10ml of the diluted solution in to a 250ml conical flask and dilute it with
100ml of distilled water.
3.Add 2/3 drops of methyl orange indicator.
4.Titrate against N/ 10 Sodium hydroxide solution to golden yellow end point.

%HYDROCHLORIC ACID (W/V) = NO. of mls of N/10 Na0H X 0.365

%SULPHURIC ACID (W/V) = NO. of mls of N/10 Na0H X 0.49

IRON
1. Pipette 10ml of bath solution into a 100ml conical flask
2. Add 10ml of dilute Sulphuric acid (1:1)
3. Titrate against N/10 KMno4 Solution until a pink color is obtained
% Fe (F/V) = No. of mls of N/10 KMno4 X 0.056