Corrosion FAQ

Why is corrosion important?

Corrosion is the main factor in the deterioration of public and private properties. If cars did not corrode, bridges not collapse and water mains not burst, there would be no need to consider corrosion as a science. But cars lose control, bridges do collapse and water mains burst with almost predictable regularity. Engineers and technicians repair obviously corroded bridge support structures but corrosion is often hidden. It cannot be seen inside structures. There are, however, technologies that can stop hidden corrosion. Corrosion engineers are the persons to call.

How much money is lost due to corrosion?

NACE International, formerly known as the National Association for Corrosion Engineers, estimated in 2005 that in the U.S. alone the annual cost to municipalities for repair and replacement of corroded items such as bridges, roads, water mains and machinery is over $36 billion dollars. In many towns and villages, the cost of water main repairs are more than 50% of the water and sewage department annual budgets.

Why do your town's water mains break?

Often heard is the statement that the water main pipe that broke is "old". True, age is a factor but it not the whole story. In northern regions, ferrous (steel and ductile iron) mains that run parallel to or that intersect roadways break, regardless of age. This is due to the chlorides from road salts. Municipalities often replace these mains with plastic lines that do not corrode but incur a great cost.

Why is it important to apply cathodic protection to water mains?

There are techniques that corrosion engineers have been using for many years to detect potential water main breaks. Where a potential main break is detected, it is by far more economical to insert anodes then to replace that section of the pipe. The cost differential is often one to ten. For example, if the cost of replacement of the pipe after it ruptures is $8,000, an efficient municipal water department team would insert an anode or two for about $800 and no subsequent rupture would occur.

Can water main leaks from corrosion cause contamination of drinking water?

Yes. For each 10 gallon of water that leak into the ground from a leaky pipe, about one gallon would be htmlirated into the water main (even though the main is pressurized). If the pipe happens to run through a town square that 200 years ago was a cow pasture, the drinking water would be contaminated.

What can be done to protect water mains?

Your corrosion engineer can teach your water department the rudiments of "over the pipeline" survey. There is no need to excavate the pipe. In "hot spots" your water department personnel can, with coaching and equipment, insert anodes next to the water pipe. Magnesium anodes normally last 20 years, during which time this section of the pipe will be protected from further corrosion.

What are anodes?

Anodes are connected to the structure that is to be protected. The job of the anode is to provide for the electron stream that steel needs so that it will not corrode.

Can cathodic protection be applied to the interior surfaces of a large water tanks?

Yes. The American Water Works Association (AWWA) in its Standard D104-97, "Automatically Controlled, Impressed-Current Cathodic Protection for the Interior of Steel Water Tanks," recommends cathodic protection by hanging anodes from the tank's roof or from a floating raft. The anodes protect the submerged steel surfaces, including the floor from corrosion.

Is it necessary to recoat (apply a new impervious paint) to the interior tank walls and to the floor?

It is not necessary to apply new coatings. Quoting AWWA D104-97 Page viii: "When properly applied and maintained, cathodic protection systems will arrest corrosion at flaws in the submerged coated surface." NACE International in Page 1 of its Standard RP0388, "Standard Recommended Practice Impressed Current Cathodic Protestation of Internal Submerged Surfaces of Carbon Steel Water Storage Tanks," states: "When cathodic protection is used on existing tanks, it is not necessary to prepare the surfaces to be protected."

By not applying a new coating and resorting to cathodic protection only, how much money can be saved?

Applying a new coat may require removing the old coatings, sand blasting the interior surfaces, and applying a primer followed by the new coatings. In 2008 dollars, the cost could vary from about $10 up to $20 per square foot of interior surface. For a 1,000,000 gallon tank, typically about 15,000 square feet, this could add up to more than $300,000, not to speak of the down-time when the tank is out of service which could be about 30 days. On the other hand, cathodic protection may be applied while the tank is in full and operation at a small fraction of this cost.

How effective is a cathodic protection program in protecting water mains?

Many towns practice this program but few keep statistics. Where statistics are available, it has been shown that within 2 years of program initiation, the rate of water main failures dropped by more than 90%.

Does concrete corrode?

Yes, both concrete and the reinforcing steel bars corrode in time. However, corrosion of the steel reinforcement is by far more aggressive. When the steel corrodes, the rust expands the volume the rebar occupies causing stress in the concrete that quickly leads to cracks and quick deterioration in the load carrying capacities of the concrete. (A rebar is a slang contraction of "reinforcement bars of steel" that are embedded in concrete.) Chlorides accelerate the deterioration. This is why bridges and concrete garage floors and ceilings do not last more than about 20 years.

Can concrete be protected from corrosion?

Yes, corrosion engineers can plan and execute successful cathodic protection systems for concrete. The cost was about $10 per square foot area of protection. Please note that protection must be applied to "hot spots" and not to the entire structure. When the cost of the entire structure is considered, cathodic protection is truly economical.

When was "cathodic protection" invented?

Accounts vary. Some say that the British Navy's Lord Nelson first applied the principles of sacrificial anodes to his ships. The US Navy knew and practiced cathodic protection during the Revolutionary Wars.

How advanced is the science of corrosion protection?

There is no domestic hot water tank, public hot water tanks or ships afloat that are not cathodically protected. Even small power boat have cathodic protection for their propellers. U.S. Code of Federal Regulations (40 CFR Part 112), mandates cathodic protection to all buried oil pipes, gas pipes, steam pipes, chemical pipes and oil tanks.

Why do my town engineers not apply cathodic protection where necessary?

A metallurgical engineer is the professional best qualified to design a corrosion prevention system. A civil engineer is more likely to replace a structure than apply an alternative that would protect it. Likewise, town engineers cannot be expected to know the details of corrosion engineering. Unfortunately, it often costs more to replace a structure or a pipe than protect it from corrosion. This lack of knowledge costs unwary municipalities.