Copper Pipe as Water Main

[ziptron]

Hi All,

I have a question that I'd like to get some feed back on.

I've looked through codes/standards of various municipalities regarding the type of materials that can be used for water main lines. They all share the typical ones:

1. Ductile Iron
2. Concrete
3. PVC

However, none of them list copper as an acceptable material to use for a water main. I am aware of the cost difference, but is that the only reason? Does copper behave poorly underground? If so, then why do they use specify copper for service connections? What would be a good source for such information?

Thanks in advance!

 

[bimr]

The extremely high cost is a big factor. Copper tubing has a thin wall material so it would be much more costly to use as the pipe diameter increases. Copper is also not as mechanically durable, does not have the tensile strength, and is not as corrosion resistant as other alternatives.

The parameters of the service installation such as pipe velocity and diameter are somewhat defined making copper more acceptable. The ease and speed of installation is probably the biggest factor for services.

 

[gerhardl]

In addition to remarks from bimr:

If you go back 50 years and more, both copper and certain brass qualities were used commonly for water, hotwater and steam pipelines, both for processes and especially for high- quality shipbuilding pipelines and accessories. The materials where not much used for diameters above 1 - 2 inch.

The reason for use was mostly corrosive resistance over time. Price compared to other competitive materials was not that large (I believe), where and if alternatives actually could be found. Pipewall thickness was far more than today.

Increased knowledge on heavy metal 'leakage' from som copper alloys has since limited the allowed use and narrowed the band of alloys allowed. The commercial cost and availabiity of copper materials, and weaker, more thinwalled standards combined with the availability and pricing of alternative materials (stainless, plastic composites and GRP) will together contribute to a very limited use, and only for special applications. Therfore: no special reason to include copper in standards or descriptions for 'mains'.

(If selecting, be sure to check against allowance regarding heavy metal deposits and water quality.)

 

[micalbrch]

In some European countries copper pipelines are not allowed for drinking water because copper can be dissolved from the pipe when the pH value is less than 7. That is interesting if one considers that nearly 50 % of all drinking water pipelines in Germany for example are made of copper. But over the years a layer of copper carbonate prohibits that copper is dissolved. That's why existing pipes do not have to be replaced. But as the layer is formed over years and not within days copper is forbidden for all new drinking water pipe systems.

 

[bimr]

The tendency of water to cause corrosion is complex and caused by many factors including the elements present in the water, temperature, pH, etc. Since there are so many factors, it is difficult to compare experiences.

Water will have either a tendency to form scale or to corrode the pipe. However, the preferred approach for municipalities is to have a water with slight scaling tendencies.

For carbonate to be present in water, the water will have to have a relatively high pH. Most waters do not have a pH high enough for carbonate to be present. If there is no carbonate present in the water, it is impossible to have copper carbonate scale form no matter how many years the pipe is in service.

The easiest method to make municipal water less corrosive is to raise the pH. However, most municipal systems refuse to do this because of the expense.

Copper is more susceptible to corrosion than other materials and that as well as cost takes copper out of consideration.

I seriously doubt that the German experience is any different than anywhere else.

 

[micalbrch]

You can doubt that, bimr. But it is true. Copper pipes for drinking water (I'm not talking about heating systems in households) are forbidden for new installations in Germany, if (and only then) the pH value is low enough so that copper can be dissolved from the pipes.

 

[ziptron]

Thanks all for keeping the very informative conversation flowing.

Michalbrch,

You say that copper is not allowed because it will dissolve in PH lower than 7, is that fact or just your interpretation of the German building codes? If anyone is aware of any studies to this effect, I'd love to learn more.

 

[micalbrch]

No, that is not so much the interpretation of the German codes but the consequence from these codes. For private reasons I had to do with that. That's why I know it. The German code itself does not list a pH value but it lists a critical value for copper in drinking water. And I was teached by the building authorities (and got that confirmed by a plumber) that copper pipes must not be used when the pH value is less than 7. I can't help you with the chemistry behind that.

 

[rconner]

While have no idea of any specific relevance, when I read this thread I went back and read the "German National" report I'd seen some time ago at

http://www.dvgw.de/fileadmin/dvgw/wasser/netze/iwa_wloss.pdf

(I was kind of amazed when for whatever reasons I saw no data whatsoever on copper for either mains or even service connections!)

 

[micalbrch]

That report is not what I would translate with German "Drinking Water Ordinance". The critical value for copper is 2 mg/l.

 

[bimr]

The poster's query involves the use of copper in water mains. For the most part, modern water systems use water mains with a minimum diameter of 8-Inch. Nobody constructs water mains made from copper. I have heard of old water mains being fabricated from wood, but never from copper. I would be willing to wager that 0% of the water mains in Germany are made from copper. In addition, the chemistry of water is the same in Germany as it is everywhere else. That is what I was referring to as the German experience.

NOte that water scale for the most part consists of calcium carbonate or magnesium carbonate, not copper carbonate.

As to the pH of water, that is just one factor in corrosion. A water having a pH of 7 will tend to be corrosive if the hardness is low and the water salts are several hundred mg/l.

There is also another factor with copper corrosion. Unlike most other materials, copper is susceptible to erosion ahould the fluid velocity exceeds 8 ft/sec.

You can find information on copper at copper.org

 

[rconner]

My surprise was related to the fact that there was no mention of copper under the "service" Fig. 7 (maybe it was covered under "other"?) I think I read some time ago that copper may have constituted up to 80% of service lines in the USA in the mid-'80's.

 

[Shawner]

bimr,

You noted that any fluid velocity over 8 ft/s can result in excessive erosion in the pipe. Just curious where you got that number (don't mean to hijack the post, just have a possible issue within our system where excessive flows through a smaller diameter pipe may cause this erosion with higher velocities)

Thanks!

 

[bimr]

Shawner, information on veloicty is on the copper manufacturers site:

2.Water at high velocity.
An undersized piping system or an oversized recirculating pump may cause high water velocity. Installation of a smaller capacity pump(s) or a throttling bypass on the existing pump(s) should help in lowering the velocity of the water in the system. The recommended maximum velocity for water in a copper tube system is 5 - 8 feet per second (fps) for cold water systems, 4 - 5 fps for hot water systems < 140º F, and 2-3 fps for hot water systems with a temperature greater than 140º F.

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