Metal finishing Q&As since 1989

-----

Suspected sulfide related cracking of CF8M pump casing - Soda ash industry

2004

We operate an Inorganic chemicals Complex (in Gujarat state In India about 980 km northwest of Bombay) The main product at the complex is Soda ash. One of the critical pumps for our Soda ash plant is suffering casing cracks due to suspected sulfur [affil links] precipitation in the system.

The duty conditions are:

Clear Liquid at 70 C
Pressure 6 kg/CM2
pH about 10
Material of casing CF8M
Composition: Sodium Chloride 270 gm/L
ammonia [on eBay or Amazon] 85 gm/L
Carbon dioxide 35 gm/L
Sodium Sulfide is dosed in the system to maintain concentration of 0.1 gm/L.

This is a recent change. Earlier we were using Hydrogen sulfide dissolved in ammonia - water for this dosing. We have changed this recently to eliminate use Hydrogen sulfide- a very hazardous material. For the last 50 years or so, we did not face the pump casing cracking problem. This is noticed only after we changed the dosing to Sodium sulfide recently.

The reaction to liberate Sulfur in Ammonia-Sodium Chloride system does not take place at temps lower than 90 °C and only in presence of Ammonium chloride but we still suspect this.

Thanks in anticipation for help,

Mr. Rahul J Buch
Head technical services, inorganic chemicals industry - Mithapur, Gujarat, India

I don't know about the cracking but for your process parameters you can use corocoated or polymer lined pumps they can give you performance better than CF8M and would be more viable techno commercially.

Amit Mahajan
- Delhi
2007