Corrosion starting in a pipe

[AO1958]

Hi everybody,
I kindly ask you an help concerning following issue:
I have found a localized corrosion in a copper tube. No other points of leakage has been found.

When sizing the tube, and examining the hole, this was characterized as an hourglass shape

- on the tube outside I localized a small crater
- on the tube inside I localized a big crater (of twice the diameter of the outside tube)
A material deposit was present in the inside part of the tube.
Unfortunately I had no possibility to realize other test, like SEM, and I have no information concerning this tube except that it was utilized for water.
Please, I kindly ask you if the above information are enough to determine if the corrosion has started from the inside or the outside of the tube.
Many thanks

 

[BrianCNTFM]

Hi AO1958, what is the fluid, is the external surface exposed to a corrosive environment. If the latter answer is no then the indication is internal corrosion though you may want to look for pitting in adjacent area it may be impingemnt. check fluid velocity through tube

Regards Brian

 

[EdStainless]

and if no other signs of erosion damage inside the tube I would suspect microbiological causes. Potable water? Does this line sit with little flow for long time periods?

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Plymouth Tube

 

[rustbuster]

Was there ant mechanical damage? I had a copper line hole through at a slightly dented area, this was the only site exibiting corrosion damage.

 

[AO1958]

Hi and thanks everybody !

To mr. BrianCNTFM
Unfortunately I haven’t got any information concerning the environment.
Concerning the internal and external surface, no evidence of other holes are present.
Please, could you tell me where I can find suggested velocities for water into tubes ?
As a matter of fact I would suppose that the problem would be the excess of velocity of water, not the low velocity.

To mr. EdStainless
As a matter of fact no evidence of erosion damage into the tube,
Which could be the microbiological causes that corrode copper ?

To mr rustbuster
There is no evidence of mechanical damage

Many thanks

 

[sw71im]

Hi AO1958,
Any compound with nitrogen (Like Ammonia,...etc) can casue a localizes corrosion to copper/copper alloy

 

[sw71im]

Hi AO1958,

Nitrogen compound(Ammonia..etc) can cause a localized corrosion to the copper/copper alloy

 

[strider6]

here you can find some good info on copper corrosion in water:

http://www.corrosionist.com/copper_pipe_corrosion.htm

http://www.copper.org/applications/plumbing/techcorner/designing_piping_systems.html

http://www.copper.org/publications/pub_list/pdf/a1061.pdf

S

Corrosion Prevention & Corrosion Control