Copper Erosion

Zman

I thought I would throw this one out there as is is a new one for me.
This is a domestic recirc pipe that has run at excessive velocity for 20ish years. The building has had many leaks where you would expect on 90's and tee's.
It is also pin holing on straight sections of pipes. Check out the inside of the pipe.

Big Ed_4

Turbulence of the moving water , How the Grand Canyon was carved ...

Zman

The gouges are the interesting part. They are noticeable and deep. One theory would be that there where inconsistencies in manufacturing resulting in weaker areas in pipe. The high velocity exposed the weakness and stripped this material first.

flat_twin

How excessive was the velocity in this example?

Zman

I am putting together a proposal to balance the system. My best guess is that the water is presently moving at 8-10 fps.
The original circulator is no longer in place. I suspect the water was moving even faster originally.

RayWohlfarth

Zman I have been told that velocities faster than 6 fps would cause erosion inside copper. I have never seen it though. Either that or its a remake of Tremors.

JUGHNE

This is 40 YO hard L copper that was in a return on a recir line.
It was just downstream of a ball valve that was partially closed for balancing. There was no copper left in the ball valve socket.
This was only noticed because of the pin hole that was spraying water.
I suspect the "tumbling" effect of the water coming out of the partly closed ball valve.

RayWohlfarth

wow thats amazing how erosion is so powerful

Gordy

Carl are the erosion areas at the bottom, or top of the pipe when in place?

Water temperature, TDS level, PH all play into this.

To me it seems as you say manufacturing. Maybe the extrusion process of the pipe, , and material inconsistency.. wall thickness maybe thinner in the eroded area.

hot_rod

Big Ed said:

Turbulence of the moving water , How the Grand Canyon was carved ...

Cavitation from a rough surface in the spillways almost took out the Glen Canyon dam above the Grand Canyon in 1983.

A rough surface caused by a concrete defect allowed the water to erode through a 3 foot thick reinforced concrete pipe in the spillway.

Here is a great read about the canon and a handful of river guides the sneaked on to the river during that high water season.

hot_rod

Zman said:

I am putting together a proposal to balance the system. My best guess is that the water is presently moving at 8-10 fps.
The original circulator is no longer in place. I suspect the water was moving even faster originally.

I think that is just the flow pattern from the excessive velocity and caviation.

Here is a fitting I cut out years ago. High velocity and extremely hot water leads to this type of pin hole.

The un-reamed copper tube may have played a big part also.

Larry Weingarten

Hello, You might want to consider using PEX and plastic fittings where possible. PEX stands up to erosion corrosion much better than copper. Also, anything you can do to reduce run-time of the pump will have multiple benefits, from limiting erosion to cutting utility bills. A rough rule of thumb is that constant recirc triples you water heating energy use.

Yours, Larry

HomerJSmith

What's the quality of the water? It's obviously a velocity problem.
Ball valves don"t balance a line worth squat. I usually use the other 's' word, but it's Sunday.

Use a real balancing valve or (a globe valve if you have to).

HomerJSmith

That looks like type L Copper. Recirc lines have a pump on it, maybe you should resize it and make sure it has a flow check on it if there is a possibility a larger pump in the system could push thru it in reverse. If that's the case a larger pump could just close off the flow check when it is running.

Zman

Gordy said:

Carl are the erosion areas at the bottom, or top of the pipe when in place?

Water temperature, TDS level, PH all play into this.

To me it seems as you say manufacturing. Maybe the extrusion process of the pipe, , and material inconsistency.. wall thickness maybe thinner in the eroded area.

@Gordy
Water temp is around 130
PH ~7.6
TDS 150
I believe the water likely has high levels of entrained air which adds to the issue

Building has all types of erosion. Some are the classic ones like hot rod pictures. Others are on the bottom of pipes in areas where there are several fittings, flux may have been over applied. The one that surprised me was the one that looked like gouges.

Zman

@HomerJSmith
Agreed, I am planning on Caleffi Quicksetter with temp gauges.

Zman

I like this feature of Siggy's software. You need very little flow in recirc lines. This is one of the most misunderstood subjects in plumbing/heating.

hot_rod

Zman said:

I like this feature of Siggy's software. You need very little flow in recirc lines. This is one of the most misunderstood subjects in plumbing/heating.

The Circuit Simulator is another great module, the 3rd one.

Zman

I agree, I found it useful even on cirs that are not in the system. You can graph the system curve by trying different circs and noting the head loss and gpm.
I used it the other day to size pool pumps

JUGHNE

Hot Rod, I did watch the webinar on Legionella Disease 11-16-17, the one you mentioned.

One thing I did come away with was in some major projects they raised the flow rates of recir pumps in order to increase the return rate of the water to get some of it back into the 140 degree tank. Hopefully to kill the Legionella if there.

So there has to be a happy medium somewhere.
I have a gravity recir system in my house and wondering if I might be cooking a stew in the recir line as the water comes back pretty lukewarm.

Mark Eatherton

A couple of things about hydrolysis.

1. Horse always walk up stream.
2. . The CDA discovered that many (most) of their previous diagnosis related to copper erosion, were incorrect. Most erosion problems relate to the acid in the flux used during the soldering of the pipes.

Lastly, the long striations I see in your examples look like they had their extrusion presses set too tight. In my 40 years, I've never seen hydraulic erosion that looked like that, and I always cut failed pipe and fittings apart to see what's going on inside. Most cases look like the ones HR showed, and are probably flux related. True hydrolysis has u shaped tracks (horse shoes) and as noted, horses always walk up stream.

I have seen a small ding in 3/4" type K soft pipe erode out a hole. Water flowing is a strange beast to follow... Just look at a stream.

ME

Mark Eatherton

Larry Weingarten said:

Hello, You might want to consider using PEX and plastic fittings where possible. PEX stands up to erosion corrosion much better than copper. Also, anything you can do to reduce run-time of the pump will have multiple benefits, from limiting erosion to cutting utility bills. A rough rule of thumb is that constant recirc triples you water heating energy use.

Yours, Larry

If you do choose to use PEX and there is chlorine in the water, make certain it has a high resistance to oxidizers. Most people don't know that there are different degrees of antioxidants used in PEX. Pipes used in circ return systems need to have a higher antioxidant package than pipes not seeing circulation.

As it pertains to tripling the energy consumption, I guess one needs to look at the resource that is being conserved, and the trade offs associated with that conservation effort. Having a good and properly controlled circ return system will completely eliminate the waste of water purging tepid water out of a given circuit to get hot water. At the expense of fuel consumption. If fuel is cheap and readily available, but water isn't, then it makes sense to do circulation. Water is our MOST valuable resource, no?

The key words here are "properly controlled" circ return system. Most circ return systems are NOT controlled. We need to start addressing this by the use of sensor (electric and or non electric) to restrict flow when hot water is readily available at the furthest end of the system, instead of waiting for the return to come back hot. If we apply off shelf technology (Grundfos Alpha for example) and use the European non electric flow modulating technology with the temperature sensing bulbs on the FAR ends of the system, the DHW circ return system will begin modulating, wasting minimal energy(s) while reducing the waste of the most critical resource, that being water.

The only thing an out of control circ return system saves, is time... and a little bit of water.

ME

hot_rod

Also, proper sizing of the recirc circulator is critical to the operation. It's rare to see an under-pumped recirculation system, most are over pumped or grossly over-pumped.

Regardless of using a smart pump or smart control, the pump size should be calculated.

hot_rod

Mark Eatherton said:

A couple of things about hydrolysis.

1. Horse always walk up stream.
2. . The CDA discovered that many (most) of their previous diagnosis related to copper erosion, were incorrect. Most erosion problems relate to the acid in the flux used during the soldering of the pipes.

Lastly, the long striations I see in your examples look like they had their extrusion presses set too tight. In my 40 years, I've never seen hydraulic erosion that looked like that, and I always cut failed pipe and fittings apart to see what's going on inside. Most cases look like the ones HR showed, and are probably flux related. True hydrolysis has u shaped tracks (horse shoes) and as noted, horses always walk up stream.

I have seen a small ding in 3/4" type K soft pipe erode out a hole. Water flowing is a strange beast to follow... Just look at a stream.

ME

Pretty much all the flux nowadays is water soluble, it should wash out when water flows?

I think the wear marks in my ell was related to not reaming the tube AND excessive velocity. The ridge on the tube is obvious in the cut a way. I'd guess that lack of de-burring to be more common of a mistake or oversight compared to flux.

Gordy

I'm still thinking extrusion malfunction in the manufacturing process.

Zman

Gordy said:

I'm still thinking extrusion malfunction in the manufacturing process.

I agree, It may have never surfaced if not for exposure to to high velocity DHW...

Gordy

Very true.