Magnetite in heating circuit more likely when it's a glycol-water mix?

[MartinLe]

I'm dealing with a sub contractor who points out that MID flowmeters are not suitable for heating circuits with added glycol, because of the magnetite.
My understanding is that magnetite forms at high temperature and high pH.
This is a cooling circuit, highest temp. will be 90°C most of the times 75°C at the hottest palce in the circuit.
pH of glycol is in the range of 7,5 - 9
Pipes are black steel (1.0254).

Water will be decarbonated before filling circuit.

My question:
Should I be concerned about magnetite interfering with the MID?

p.s.: The sales engineer for the flowmeters strongly discouraged MID and argued for ultrasonic flow meters, as for now I'll go with this.

 

[Ziggypump]

You have a "cooling" circuit at almost boiling? I'm curious what your fluid cooler or chiller operates at.

OK, magnetite is nasty, but taking steps to filter it is helpful. I know that bad water quality and glycol mixed does produce an acidic solution that will eat at the pipes creating magnetite, but a properly maintained water quality shouldn't create a bigger issue than needed.

With using glycol, I'm assuming it's a closed loop system. In this case, what are you using for an air separator? Caleffi has air separators and air scoops that include magnets to draw the magnetite out of the water. If water quality is a concern an air/dirt separator would be the absolute minimum. The Caleffi magnets protrude into the air separator in a sleeve so the magnetite stick to the interior of the separator. You shut down the system, remove the magnets (draining isn't needed for this) and blow down the air separator. Check it out, it's a pretty inventive idea.

My first thought is why use glycol if the water temperature doesn't approach freezing? Second would be install better filtration equipment if water quality is a concern.

 

[MartinLe]

It's a cooling system for a cogeneration plant, circuit between engine and air chiller. Most of the time the engine heat won't go through this circuit but feed into a heating system. It's mostly inactive so freezing can be a concern.

Closed loop system, water will be pretreated for hardness before filling.

My main concern was with the flowmetering but that's allready answered.