Types of Corrosive Water

Mian Muhammad Bilal

Muhammad Hamad Saeed

Sea waterFresh water High purity waterBrackish waterWaste waterPotable waterDistilled waterCooling water

Sea WaterSeawater or salt water is water from

a sea or ocean. On average, seawater in the world's oceans

has a salinity of about 3.5%.This means that every kilogram (roughly one

litre by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts.

Sea water can act as a good electrolyte and can cause galvanic corrosion and crevice corrosion.

Corrosion cause by sea water depend on oxygen content, velocity, temperature and biological organisms.

Effect of oxygen

Effect of pH

Factors which aggravate marine corrosionPitting and Cavitation

Stress Corrosion

How can marine corrosion be controlled? Protection by painting 

Cathodic protection

Inhibition 

Galvanic corrosion

Using corrosion resitant alloys

Metals and Alloys that are normally use in seawater areTitanium, copper nickel alloys and nickel chromium molybdenum alloys.

Fresh water Corrosivity in fresh water varies depending

upon oxygen content, hardness, chloride content.

Depending upon the minerals dissolved fresh water can be

Hard water Soft water

Soft waters are usually more corrosive than hard water.

Cast iron, galvanized steel brass, aluminium are most widely used materials for handling fresh water.

High Purity Fresh waterAs the purity of water increases corrosion

resistance increases.It is normally use as a heat transfer

medium.Intergranular attack and cracking of

solution quenched stainless steels and alloys occur in high purity water containing oxygen.

WASTEWATER is the fancy term applied to water that is contaminated by human activity such as bathing, dishwashing and flushing the toilet or it may be of industrial waste.

Globally, two million tonnes of sewage, industrial and agricultural waste is discharged into the world's waterways.

Waste water

While traveling through sewer lines, the wastewater can become anaerobic or septic as a result of the metabolic processes of microbes commonly found in wastewater

Under anaerobic conditions, specific sulfate-reducing bacteria thrive. These microbes generate hydrogen sulfide (H2S) as a byproduct of their respiration

Waste water constituents

H2S has a low solubility in wastewater and when it escapes from the wastewater and moves into the air it is easily recognized by its characteristic offensive, rotten-egg odor.

H2S can also be responsible for severe corrosion problems and toxic

conditions. So the corrosion invovled isBiological corrosion.

Waste water corrosion

Waste water disaster

Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water.

Brackish water

Brackish water contains between 1 and 2.5% sodium chloride, either from natural sources around otherwise fresh water or by dilution of seawater.

Brackish water differs from open seawater in certain other respects. The biological activity, for example, can be significantly modified by higher concentrations of nutrients.

Brackish water

Any compound capable of donating free chlorine ions (Cl -) to an aqueous (water-based) solution has the potential for causing failure in stainless steels. The chlorine ion is extremely electronegative, and therefore very reactive with certain compounds and elements. 

Corrosion

Chloride attack of stainless steel is spreading out evenly as rust does. So thin tubes and pipes will not necessarily last much longer than thick ones before failing due to chloride induced corrosion.

Chlorine effect on corrosion:

Case study

The observed cracking of monel alloy bolt in service is due to MIC by SRB.

Inter granular corrosion attack on the grain boundaries was by MIC.

The only conceivable source of sulfide in this case is bacterial activity of Sulfate Reducing Bacteria (SRB).

The sulfides can cause breakdown of the passive film layer on the Monel alloy.

Thus making it susceptible to intergranular corrosion by chlorides.