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AC current & inner pipes corrosion

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e573

e573

Electrical
May 11, 2001
7
We often see "pin holed" inner steel water pipes in buildings
 (corrosion from the inner side of pipe).

If it is possible, some questions on this item.

1.  Can the AC current on internal pipeline systems of buildings
 result in of their accelerated "pin hole" corrosion.

2. What values of AC currents definitely cause "pin hole" corrosion of
 internal steel pipes of buildings (i.e. what values of currents it is necessary
  to consider dangerous).

3. To what extent  the use of   cathodic protection (at presence and absence
of AC currents) can solve this this problem of inner corrosion of pipes in buildings).

4. Is it necessary to implement  the elimination of AC currents on internal
 water pipes, in view of operation others chemical, electrochemical and bacteriological
  making of the process of corrosion.

5. Is it possible to  to give an expert estimation of the contribution
 in intensity of corrosion processes of inner water steel pipes in buildings
  only to a component, bound with AC currents, on a background of all band
   of the  factors   of an internal pipes.

6. Means elimination of AC  currents on pipes complete termination of the process
 of corrosion, or it is possible to speak about its deceleration; and, in the latter
  case, up to what degree.

7. What literature is available on this item.


Thank you very much in advance.
 
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Are you sure it's not just pitting due to dissolved oxygen? In addition, lots of places try to cut corners, using cheaper carbon steel pipe in applications where they really should be using copper or stainless steel. I've also seen erosion of the piping due to very high, sustained velocities as a result of undersized pipe. This type of failure typically occurs in places like 90* elbows.

You could have piping failure problems due to electrical weirdness, I suppose, but I'm not aware of that happening anywhere other than buried systems. I'd be much more inclined to think of chemical/mechanical causes, and my experience is that about 75% of all of the problems that are considered to have a chemical solution to deal with them, actually have a mechanical root cause. Select the right equipment/piping material for an application, install it properly, and you've solved most of these problems before they've even started.

 
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There is physics principle covering the flow of current in conductors that makes AC or DC stray current effects inside a water pipe "impossible". Stray current effects involve current entering and leaving a conductor, with corrosion concentrated where the current enters (i.e. electrons leave).

This is a common problem from dissolved oxygen and no one can predict where the pitting will be first through the wall. Water lines made of carbon steel always have this unless the water is dearated or inhibited, neither of which is practical in so-called "drinking water" systems.

Some systems may be protected with internal Cathodic Protection - usually a ribbon of Zinc inside the pipe - but this is more the excetion than the rule.
 
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Dear Rustbuster1, thank you very much for your answer.
But what the physics principle do you mean, I am very interested to know them better.
Thank you again.
 
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The physics principal I was recalling is the skin" effect. Current per unit cross-sectional area is known as current density. It is expressed in amperes per square meter, amperes per square centimeter, or amperes per square millimeter. Current density can also be expressed in amperes per circular mil. In general, the greater the current in a conductor, the higher the current density. However, in some situations, current density varies in different parts of an electrical conductor. A classic example is the so-called skin effect, in which current density is high near the outer surface of a conductor, and low near the center. This effect occurs with alternating currents at high frequencies. Another example is the current inside an active electronic component such as a field-effect transistor (FET).


All I really wanted to insist is that stray currents DO NOT OCCUR inside a hollw metallic conductor, which the water pipe would effecively be.
 
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