Copper pipe annealing

[MedicineEng]

Hi All:

We are having quite a few copper pipe leaks in our property's hot water system.

These occur almos exclusively in the vicinity of elbows and by the damage profile seems to be provoked by erosion corrosion due to high water velocity. We measured the water flow at the balancing valves and it seems to be well below the typical 1.5m/s. Since the leakages are clustered in a couple of locations instead of spread all over the property, seems to indicate a local problem and not a property wide one, like incorrect chemical treatment for instance.

One of the hypothesis being thrown in the air is workmanship and copper annealing, being that there was an overheat of the metal during brazing process , which annealed the metal and made it permanently softer and thus more subject to the effects of erosion corrosion.

I was trying to find some technical paper to support the theory that overheating copper pipe permanently softens the material, but I was not able to find it.
Is this just a myth or is there any truth behind this?

thanks for your help.

 

[MintJulep]

I'd suspect workmanship during installation.

Overheat during brazing.
Too much, or too little solder.
Not deburring pipe ends.

Burrs and solder ridges can initiate cavitation.

 

[EdStainless]

Or residual flux on the inside of some fittings.
Or a lot of fittings that are either softer or thinner than others.
In some water quality (very soft) hot water will erode Cu very quickly.
You can use long radius elbows and move to a heavier wall for the Ells, such as 'M' or 'K' rather than the more typical 'L'.

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P.E. Metallurgy, consulting work welcomed

 

[mrfailure]

Send a sample containing a leak to a lab that can analyze using destructive failure analysis techniques (visual, cross-sectioning, microhardness) to see.

 

[TugboatEng]

How hot is the water? Water close to it's boiling point may cavitate in the turbulence downstream of fittings.

 

[WKTaylor]

Also, be aware that extremely fine silt/sand particles in the water... even in low concentrations... may also be a factor.

Also, verify that the copper alloy is exactly as specified for hot water system. Pipe and fittings that are supplied without verified source and certifications may also be prone to in-service damage like this.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[MedicineEng]

Thank you all for your feedback.

Just some more information:

1. sample was sent to lab that confirmed that complies with alloy C12200
2. Hot water is maximum 65C (typically between 48-55C)
3.

My initial question was if overheating during brazing can lead to permanent annealing of the copper pipe and thus make it softer and more damage prone.
Any thoughts on that?

Thanks.

 

[TugboatEng]

Your velocity is too high for the temperature.

Water velocity in copper tubes should not exceed 8 ft/s (2.4 m/s) for cold water and 5 ft/s (1.5 m/s) for hot water (up to approximately 140oF, 60oC). If water temperatures routinely exceeds 140oF - don't exceed 2-3 ft/s (0.6-0.9 m/s).

https://www.engineeringtoolbox.com/pressure-loss-copper-pipes-d_930.html

What is the static head pressure on the system? You may consider enclosing it and using a hydropneumatic tank to increase the static pressure to prevent cavitation.

 

[EdStainless]

These fittings are supposed to be annealed when you buy them so I cannot see that the heat from brazing would have any impact.
I like TBEs post, velocity in hot water is a big deal.

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P.E. Metallurgy, consulting work welcomed

 

Looks like you've got a classic case of erosion corrosion. Nothing to do with annealing.

1) Ensure your system is sized correctly to limit flow velocity.
2) Turn down the water temperature to 60°C or lower.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."