What Is Scale

1. What is Scaleflow, Scaleclean - A, and Neutraflow?

Scaleflow, Scaleclean - A, and Neutraflow is a revolutionary descaling agent. In other words, it is inhibited hydrochloric acid for general use in all types of chemical descaling operations. It removes water hardness scales, deposits from steam and hot water, mill scales, weld scales, moulding, foundry deposits and many other types of foreign residues on metals.

Scaleflow, Scaleclean - A, and Neutraflow in addition to inhibitors, also incorporates wetting agents to assist the solvent action of the acids on the deposits to reduce 'drag out' losses, absorption of inhibitors by scale, rust and helps the solution to penetrate into inaccessible regions.

2. What is Scale?

A scale is a hard water soluble substance formation or incrustation resulting from the general deposition of dissolved solids in water, over heat transferring metal surfaces.

The principal scale forming material, coolant water is calcium carbonate (CaCO3), a hard tenacious adherent baked scale. Other scale forming constituents are magnesium hydroxide, calcium sulphate and silica. Other types of scales which are formed on hot or cold worked metals consist of metallic oxides, sulphide and other components.

The solubility of different salts in water is given Below

3. How Are Scales Formed?

When heat is applied to water containing bicarbonate, the CO2 is expelled from Calcium compound. Since the relatively high solubility of Calcium bicarbonate is due to this gas, CaCO3 is precipitated rapidly as soon as the gas is removed. Removal of CO2 by chemical means the same results should be obtained & the precipitation of non-carbonate of calcium follows. As a result of this phenomenon calcium carbonate is precipitated within the boiler/equipment, forming a scale.

Also calcium sulphate, owing to its insolubility at high temperature, is precipitated rapidly. Unless it is converted into some other form by chemical treatment or removed from water as it is formed, it causes a hard, dense scale which adheres tenaciously to the internal metal surfaces of the boiler/equipment.

The problem of deposition of boiler / equipment scale is primarily one of the solubility at elevated temperature i.e. certain slightly soluble substances become less soluble with increase in temperature. The whole body of a boiler solution constantly tends towards a state of super saturation as steam is removed.

In addition, since scale forming substances decreases in solubility with increase in temperature, the film of boiler water adjacent to a heating surface may be relieved by spontaneous crystallization, possibly promoted by irregularities in the surfaces even when vaporisation is taking place.

The growth of deposits is accelerated by the effect of skin friction at the internal surface of the tubes, since the velocities along the tube wall are much smaller than those near the centre of the tube. Deposition of silicate scale might not otherwise develop in the presence of the minimal amount of siliceous materials in feed water.

4. Descaling Chemicals

"SCALECLEAN - A" is a liquid preparation with Hydrochloric Acid base, designed to dissolve industrial deposits without affecting metals. "Scaleclean - A" is supplied in fully inhibited and concentrated form and is to be diluted with water for use. In general, any type of equipment on which scale has been deposited, can be cleaned by using "Scaleclean - A".

"SCALFLOW" is specially developed for removal of hard scale like silicate of calcium, magnesium, sulphates, carbonates etc. "Scaleflow" is supplied in fully inhibited and concentrated form and is to be diluted with water for use.

"NEUTRAFLOW" is a liquid preparation with an alkaline base. The "Neutraflow" treatment has the effect of swelling up the scales through hydrolysis of the scale components. The result is that the subsequent "Scaleclean - A" or "Scaleflow" treatment becomes faster and more effective.

5. Operational Hazards Caused By Scales

Some of the operational difficulties caused by scale deposits are:

• Obstruction of fluid flow
• Impedance of heat transfer
• Wear & tear of metal parts
• Localization of corrosion attack
• Metal failure at hot spots under scale deposits (plate)

Metal oxide scales (Mill scale, rust, etc.) must be removed from metal surfaces before painting, galvanizing, tin plating, and other principal metal-finishing processes.

6. Why De-scale With Scaleflow, Scaleclean - A, Neutraflow?

Scaleflow, Scaleclean - A and Neutraflow use HCL as the principal agent.

Calcium Chloride, Iron Chloride, etc., which are formed by the reaction of scale, are highly soluble with HCL in water.

The time taken for the solution of rust or scale is minimum in HCL as compared to other acids.

The solution rate of mill scale is 10% to 27% higher in 10% & 5% HCL, respectively, than in similar solutions of H2SO4.

A dark slime or "smut" left on metal surfaces pickled in other acids is not present when HCL is used.

During pickling in HCL, the scale is directly dissolved by the acid, and the "mechanical effect" of removal of scale by hydrogen bubbles (formed by the reaction between metal and acid) is not required. Accordingly, HCL can be inhibited with strength inhibitors.

The degree of Hydrogenation and, consequently, Hydrogen embrittlement are absent when HCL is used.

No heating is required during cleaning with HCL, as the acid dissolves the scale at normal temperature.

The tolerated iron content in pickling solutions is higher when HCL is used.

The corrosive action of HCL on clothing and skin is milder.

In general, any type of metallic equipment on which scale has been deposited can be cleaned by Scaleflow, Scaleclean-A, and Neutraflow. Typical examples of equipment include Boilers, Economizers, Super Heaters, De-aerators, Vents, Condensers, Stage Heaters, Heat Exchangers, Surface Condensers, Feed water treating equipment, valves, miscellaneous equipment, piping, water mains, oil wells, equipment used for acidizing of oil wells (to improve yields of oil from oil-bearing limestone formations), air-conditioning equipment, canteen equipment, stabilizers, electric boilers, kettles, surgical instruments, immersion heaters, heating coils, sugar and caustic evaporators, black liquor evaporators in the pump industry, railway carriages and bus bodies, brewery equipment, steel strips and sections requiring pickling, cold drawing, etc.

7. Procedure To Be Followed In Descaling The Equipment

1st Stage: Take "NEUTRAFLOW" and mix with water in the ratio of 1:6 (One litre of NF and six litres of water). Circulate the solution or immerse the equipment in this solution for 2 hours. This will be helpful in loosening the rock-hard scale. It will also help to remove oil & grease from the surface.

2nd Stage: Flush the entire system with ample fresh water, for at least 15 to 20 minutes.

3rd Stage: Take "SCALEFLOW" and mix with water in the ratio of 1:6 (One litre of SF and six litres of water). Circulate the solution or immerse the equipment in this solution for 6-8 hours.

4th Stage: Flush the entire system with ample fresh water, for at least 15 to 20 minutes.

5th Stage: Take "NEUTRAFLOW" and mix with water in the ratio of 1:6 (One litre of NF and six litres of water). Circulate the solution or immerse the equipment in this solution for 2 hours.

6th Stage: Flush the entire system with ample fresh water, until the pH of the inlet & outlet of fresh water matches.

The information contained in this technical bulletin is adequate for common descaling problems, but if further information is required, please write to us giving details of the equipment to be de-scaled and the type of scale encountered.