Turbulence corrosion

[Beelbeebub]

I've heard about it, but never seen it.... Until today.

 

Some context. 

 

This 15mm pipe (0.7mm wall) was just downstream of a flow restrictor valve (so pretty turbulent) which has run continuously at 8-10lpm for about 10 years. The water is very soft but more or less pH neutral. 

 

I noticed it was weeping at the push fitting onto the restrictor body and removed it to refit. 

 

The pipe was paper thin, I actually crushed it with my fingers. 

 

There were numerous pin holes out to about 25mm from the pole end and the inside was very pitted, almost rusty in appearance. 

Edited January 13 by Beelbeebub

[PNAmble]

My dad built a timber frame house about 30 years ago. Doing most work himself including the copper pipe work.  Over the last few years he’s had a quite a few leaking via pin holes. Last year he changed his kitchen and found that some of the pipe work had been leaking for quite a few years.   His investigation about why this was happening came up with that about 30 years ago the Chinese started providing copper pipes to the UK but they were of inferior smoothness internally which created eddys which eventually created the pin holes.   

[SteamyTea]

Soft water has more 'spaces' for other elements to get into. 

Water is the universal solvent, and not always to do with the ph.

Then there could be some cavitation happening because of the restrictivor.

Cavitation is just 'bubbles of nothing', the damage is caused by the energy caused when water rushes into the cavity.

Energy is mass times velocity after all. So a lot of little masses, moving very fast, can do damage.

[Conor]

That's cavitation. What kind of "flow restrictor" are you talking about? Throttled valves are bad news all round.

 

For big pressure gradients (6bar or more) on water mains, we use two PRVs inline to step down pressure and reduce cavitation. When you spend £10k putting something in the ground, you don't want to replace it in 5 years.

[Beelbeebub]

The flow restriction was a plastic cartridge with an o-ring, similar to this

 

 

Full disclosure: the pipe end probably hadn't been deburred either. 

 

The pressure drop was relatively small, 2bar absolute max, usually 1 bar or less. 

 

The restriction is downstream of some filters before some storage tanks. It's there to ensure a relatively steady flow over time as the filters block.

 

Flow speed was around 1m/s 

 

The pipe downstream did have a thick coating of green oxide.