restricted flow in copper pipes, rust buildup

I have a 35 year old house with copper pipes. Our water has a good bit of iron and for a long time the people who lived here before us did not have a water softener. I've opened the lines a few times for various repairs and find what I believe is buildup of iron. When it's wet it looks and feels a bit like rusty colored seaweed built up on the walls of the pipe. Once it dries it turns to very fine rusty powder, about the consistency of talcum powder, and is easily wiped out or blown away.
I have normal range at the pressure tank (45-60psi) and good flow rate at the base of the pressure tank, but many fixtures in the house, especially the outdoor faucets, have low flow rate.
My question is how can I remove this iron deposit, or whatever it is, from the inside of the pipes. I've googled this a little and have not found a description that quite matches what I see inside my pipes. There are many articles on mineral buildup, crystalline materials, and all kinds of hard deposits. But my deposits are very soft and easy to remove. Could I, for example, drain down the whole house piping system, blow compressed air through the lines starting at the top of the house to dry out all the lines and then turn the water back on to flush out the powder? Would this work or would the pipes stay too damp for the rust to turn into powder?
Any suggestions welcome.
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You might just take a look at the fixtures themselves. The house that I'm living in had a severe flow problem due to rusted galvanized pipes, but that said the flow increased dramatically from simply replacing the valves and faucets that had become clogged with rust and mineral deposits. Also, if the stuff in the copper is like you said not hardened on it should flush out quickly if flow can be restored. Just a thought.
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Drain the pipes and then turn the water back on with one of the taps open. If you can turn the water back on quick enough the surge of water through the pipes will blow a lot of sediment out the faucet, remember to remove the screen on the tap or it will immediately clog. Do this repeatedly for each faucet and you will move lots of junk. The trick will be to drain the pipes enough. You may have to cut into somewhere close to your supply and add a drain. At the same time add a 1/4 turn ball valve. This will allow you to turn the water on real fast and let the air and water surge scour the pipe.

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EXT wrote:

its a interesting problem, i suspect much of the clogs might be right at the fixtures.valve passages can be small
if regular flushing doesnt help you might try isolating one line and opening both ends, flush violently with a water compressed air mix. My vans heater cores clog and thats what the local radiator shop does, amazing what comes out the exhaust. exhaust the line to outside so you dont make a mess indoors
I have used acid to fix toilets, do your toilets flush good? i have found rim holes and internal passages plugged, pour n acid, wait 10 minutes flush normally several times to elminate the acid.
i am not suggesting you flush your lines with acid, just showing the comparision
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