Erosion Corrosion in Galvanized Steel Pipe?

[nuuvox000]

I have a building where they're trying to add a bunch of plumbing fixtures without upsizing the pipe from the street. I'm estimating the new velocity will be about 12 ft/second. I know that copper pipe can get eroded in velocities over 8 ft/s but I can't find much information on galvanized steel pipe. Does anyone have experience or knowledge on this? Thanks!
Edit: galvanized pipe is existing and in the ground.

 

[LittleInch]

You might be better off looking in / searching and posting in the water treatment and distribution forum.

It seems high alright.


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[nuuvox000]

I will do that, thank you.

 

[PEDARRIN2]

The use of galvanized pipe in a domestic system is not a current approach. A galvanized pipe "might" be more resistant to erosion initially, but once you break that galvanic coating, you now have a more reactive set up than if you did not have galvanized coating at all. There are other piping options which would likely be better.

 

[nuuvox000]

Pedarrin2, thanks, I should have mentioned that the galvanized pipe is existing.

 

[1503-44]

Duplicate post

https://www.eng-tips.com/viewthread.cfm?qid=496415

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[LittleInch]

That was my suggestion....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Bad idea. What little Zn there is on the ID will be gone soon. And in the process but a bunch of white stuff into the water.
I don't worry too much about galvanic corrosion when part of the Sn is gone, the rest will be gone pretty soon.
The problem is that the corrosion film on Fe is a mixture of oxides and hydroxides and it is soft. This flow will scour it off and accelerate the metal loss. How fast this happens will depend greatly on the exact water quality. If the water is fairly hard it will take some time, if the water is soft it will be faster.

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P.E. Metallurgy, consulting work welcomed

 

[nuuvox000]

Thank you! I ended up telling them I don't recommend it and they could have some serious leaks or water hammer issues. They're going to see if they cut down on fixtures (flush valve to tanks) or replace the pipe with something larger. I also gave them the option to use a drawdown expansion tank in the building so I think we'll figure it out somehow.

 

[bimr]

Agree with PEDARRIN2's comment. The reason people no longer use galvanized pipe is that it has a very short service life. It is common for galvanized pipe to plug up from corrosion.

Where did you come up with the velocity? Many fixtures now are very low flow and the water demands are much less than the past. It used to be 2 gpm per faucet, now it is 1 gpm per faucet.

 

[PEDARRIN2]

Lavatories, sinks, and showers are definitely lower flow rates from previous (past) fixtures. But flush valves have not decreased the flow rate, just the flow duration. They are still around 25 gpm. So, two or three flush valves opening close to the same time will flow 75 gpm, even though they may only flow for a very short period of time and total volume might only be 3.84 gallons.

 

[TugboatEng]

If the flow is only for a short duration and requires an extreme outlier case, perhaps the wear on the galvanized coating won't be so significant.

 

[hacksaw]

the steel pipe is only galvanized on the outside, not internally.

 

[LittleInch]

Some is and some isn't appears to be the response. Without cutting out a section it's probably rather difficult to find out though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hacksaw]

Mixed response for sure, but internal coating certainly not used in industrial applications.

 

[TugboatEng]

On the positive side, steel pipe needs high flow or it will corrode and clog

On the negative, high flow causes erosion and will eventually cause the pipe to perforate.

Somewhere in the middle is where you want to be to achieve maximum life expectancy. Alas, it's steel pipe so it's going to fail.

 

[PEDARRIN2]

For domestic water and dry pipe sprinkler systems, the coating is on both interior and exterior of the pipe.

 

[FacEngrPE]

You should inspect the galvanized pipe as it has been in service a while. If the galvanizing has has ANY pinholes you may have a full on case of internal Tuberculation, The picture blow shows one of the alternatives to replacement, before and after.

https://www.wwdmag.com/pipe-distribution/article/10931814/how-to-extend-the-life-of-a-water-main

 

[georgeverghese]

Why not GRE pipe ? - 12fps should be okay and pressure drop would be less

 

[GD2]

12 f/S seems to be a lot of velocity for plumbing service. Ideally, drinking water service uses PVC/CPVC at @ 5-8 ft/S. CPVC is preferred for the hot water service than PVC.[pre][/pre]
Obviously, if they want to cut cost now, they have to pay more maintenance cost later.

GDD
Canada