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71 Cards in this Set
- Front
- Back
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What is an electro chemical reaction? |
Occurs when chemical changes are produced by electricity (electrolysis) or electricity is produced by chemical changes (galvanic action) |
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What is the best measure of the corrosivity of soil? |
Soil resistivity, measured by a soil resistance meter |
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What is one advantage and one limitation of using zinc compounds over lime or caustic soda for corrosion control? |
Scale is less apt to be a problem with zinc compounds Zinc compounds are more expensive |
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How can the proper chemical dose be determined to produce water that is just saturated with calcium carbonate? |
1. Graphic methods 2. Trial-and-experiment calculations with a computer 3. Use of the marble test, Langelier index, or an Enslow column |
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How can the corrosivity of water be reduced? |
By treating the water so that the water is saturated or slightly super saturated with calcium carbonate |
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What 4 chemicals may be added to waters to reduce the corrosivity? |
Quicklime Hydrated lime Caustic soda Soda ash (these four alkalis increase alkalinity, which reduces corrosion) |
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How can pits be started on a metallic surface underwater? |
By anything that will shield the metal surface from dissolved oxygen in the water, such as bits of clay, dirt, sand, or a colony of bacteria |
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List the five CHEMICAL factors that influence corrosion |
pH, alkalinity, chlorine residual, levels of dissolved solids and dissolved gases, various minerals |
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What is a dangerous corrosion inhibitor? |
One that acts on the ANODE reaction. If not enough inhibitor is added, severe pitting will result and corrosion will be worse then if no inhibitor had been added |
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If routine monitoring indicates that a lead and copper problem exists in the source water feeding the distribution system, the utility must remove the contaminant from the source water by selecting one of which treatment methods? |
1. Coagulation+filtration 2. Ion exchange 3. Lime/soda softening 4. Reverse osmosis |
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The 2007 revisions to the lead and copper rule enhance the implementation of the 1991 rule in which areas? |
1. Customer awareness 2. Lead service line replacement 3. Monitoring 4. Treatment |
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To achieve calcium carbonate saturation, which chemicals should be added to waters with HIGH levels of HARDNESS and ALKALINITY? |
Caustic soda, soda ash (these alkalis don't increase hardness like quicklime or hydrated lime do, just alkalinity) |
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Which biological factors influence corrosion? |
Iron bacteria Sulfate-reducing bacteria |
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Which chemical factors influence corrosion? |
Alkalinity Chloride and sulfate Dissolved oxygen Hardness pH |
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Which physical factors influence corrosion? |
Soil moisture Stray electric current System construction System pressure Temperature of water |
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What is a negative side effect of controlling corrosion using silicates? |
May reduce the useful life of domestic hot water heaters due to glassification |
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What is the major use of sodium polyphosphates in water treatment? |
To control scale formation in waters that are super saturated with calcium carbonate |
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What is an electrolyte? |
A substance which dissociates (separates) into two or more ions when it is dissolved in water |
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Chloride and sulfate ions in water may inhibit the formation of what? |
They inhibit the formation of protective scales by keeping hardness ions in solution They are bad because corrosion will occur |
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How do chemical inhibitors control lead and copper in distribution systems? |
By forming a protective coating over the site of corrosion activity |
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What are the excepted potable water corrosion-control treatments? |
1. pH and alkalinity and adjustments (to reduce acidity) 2. Calcium adjustment (to form protective calcium carbonate films in plumbing) 3. Phosphate or silica-based inhibitors (to form protective films in plumbing) |
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What is the definition of an action level in the lead and copper rule? |
The value measured in the 90th percentile at the consumers tap |
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How can internal pipe corrosion be detected? How can it be controlled? |
-by rusty water complaints and by examining the insides of pipes for pitting and tubercles -treat the water to achieve calcium carbonate saturation |
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How can electrolysis of water mains be caused by other utilities? |
From currents generated by cathodic protection installed by other utilities |
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What do Rusty or red water complaints indicate? |
The water is corrosive |
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What is the meaning of pHs? |
It is that pH where water is just saturated with calcium carbonate |
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The Langelier Index is defined by what equation? |
LI=pH-pHs |
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How can water be tested to determine if it is under saturated or super saturated with calcium carbonate? |
1. Marble test 2. Langelier Index |
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When is a water considered stable? |
When it is just saturated with calcium carbonate |
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What toxic metals may enter drinking waters from the customers plumbing due to corrosive water? |
Lead, copper, cadmium |
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What does a loss of dissolved oxygen in the water flowing in a distribution system indicate? |
That the water contains organic matter or that corrosion is occurring |
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How can you detect a film of calcium carbonate that is too thin to see? |
By placing a drop of hydrochloric (HCl) acid on an obvious cathodic area and observing the area for effervescence (bubbles) |
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How can corrosion rates be measured |
By inserting steel specimens called coupons in water mains. After a period of time, the coupons are removed and the loss of weight is measured. |
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What is a tubercle? |
A small protective crust of rust that builds up over a pit caused by the loss of metal from corrosion |
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Where can an oxygen concentration cell be started? |
In the dead end of a water main |
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What is the most common type of corrosion cell? |
The oxygen concentration cell |
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What is the impact of calcium carbonate on corrosion? |
A thin film or coating of calcium carbonate can drastically inhibit corrosion |
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Why does water with a higher dissolved solids content have a greater potential for corrosion? |
Because of the increased conductivity of the water |
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What will happen if a copper service line is connected to a steel water main? |
The cathode (copper) area is large relative to the anode (steel) and corrosion will occur at the anode |
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What happens when copper and lead solder are in contact? |
The lead becomes the anode and will corrode in preference to the copper (cathode) |
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What happens to an iron water pipe when the pipe is connected to a copper pipe? |
The iron pipe will corrode into the water if the water contains dissolved oxygen |
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Electrochemical corrosion caused by the joining of dissimilar metals is called what type of corrosion? |
Galvanic corrosion |
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How can external pipe corrosion be detected? How can it be controlled? |
-by observing pinhole leaks or rust on the outside of pipes -by the installation of the proper bonds and insulating fittings, and by the use of cathodic protection |
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Why is the application of cathodic protection practical in treatment plants? |
To protect mixers, tanks, flocculators, clarifiers, and filter troughs |
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What is the C-factor? |
The C-factor designates the coefficient of roughness with a pipe A high C-factor means a smooth pipe A low C-factor means a rough pipe A C-factor is a cool factor and another word for cool is smooth. Smooth factor |
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What are the health effects of copper? |
Stomach and intestinal distress Liver damage Wilson's disease-The inability to metabolize copper |
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What are the health effects of lead? |
-Damage to the brain, red blood cells, and kidneys -Slows down mental and physical development of growing bodies -Young children and pregnant women are at the greatest risk |
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What problems are caused by iron and manganese? |
-Iron and manganese may accelerate biological growths, further exacerbating taste, odor, and color problems -stain clothes -Causes reddish-brown or black color in water |
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What 2 methods are used to treat iron and manganese? |
-lime softening -oxidation by chlorine dioxide, chlorine or other oxidizing agent |
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What is used to accomplish water softening? |
Lime and soda ash |
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What is the acceptable water hardness level? |
Up to 50 mg/L |
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The degree to which a particular metal will become anodic (corrode) in a galvanic reaction is related to what? |
Its tendency to enter into solution |
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The more active metal of any two in the galvanic series will always become what? |
The anode |
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What two metals are commonly used as sacrificial anodes? |
Zinc and magnesium |
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Is very reactive metals are called what? |
Base metals |
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On the cathodic side of the galvanic series, the least reactive metals are called what? |
Noble metals |
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What type of coupling is used to separate copper and steel? |
A dielectric coupling, which is partially constructed of ceramic, plastic, or other non-conductive materials |
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What happens when the cathode area is small relative to the anode? |
Corrosion will not be a problem |
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What six physical factors affect corrosion? |
-System construction -System pressure -Soil moisture -Stray electric current -Temperature: corrosion increases as temperatures increase -Flow velocity: corrosion is caused by low flows and high flows |
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What must be present for water to be corrosive? |
Oxygen |
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What is a common source of lead from plumbing? |
Copper tubing with soldered fittings |
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What will high levels of copper in corrosive waters produce? |
Bitter or metallic taste Green stains on plumbing fixtures |
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How does the marble test indicate whether the water was supersaturated or under saturated with calcium carbonate? |
Add a pinch of powdered calcium carbonate. If the pH, alkalinity, or calcium have increased, the water was under saturated If they have decreased, the water was supersaturated |
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How does the Langelier Index indicate whether the water is supersaturated or under saturated with calcium carbonate? |
A positive Langelier Index (pH greater than pHs) indicates that the water is supersaturated with calcium carbonate A negative means that the water is corrosive *This is the most COMMON index used to test calcium carbonate saturation* |
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What should be added to waters that have a LOW HARDNESS and ALKALINITY in order to form calcium carbonate? |
Quicklime and hydrated lime These alkalis will increase alkalinity and hardness |
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What may be added to waters with high levels of hardness and alkalinity in order to form calcium carbonate? |
Caustic soda and soda ash But the pH must be increased |
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Where in the treatment process should lime be fed to the water? |
After it has passed through the filters, but before it enters the clear well |
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What are the three hazards of caustic soda? |
-Dissolves human skin -Produces heat when mixed with water -reacts with amphoteric metals generating hydrogen gas, which is flammable |
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How can scale indicate whether water is just saturated or supersaturated with calcium carbonate? |
Water that is just saturated with calcium carbonate will form a scale only on the CATHODIC corrosion areas, but water that is supersaturated will form a scale on all surfaces |
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How does water temperature affect calcium carbonate? |
Unlike most salts, calcium carbonate is less soluble in hot water Hot water pipes can become plugged with calcium carbonate |
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What is a first-draw sample? |
The first liter of water collected from a tap that has not been used for at least 6 hours |
