Metal pipes for 30bar+

[FighterAce]

I recently decided to switch my air tank on the M4 from PVC to all metal parts... The PVC I've been using is rated to 20 bar but I'm afraid it will blow if I go any higher then 12 bar. So... my worry is that the metal pipe witch I plan on using will blow at 30 bar witch is my target pressure.
And if you want to tell me ask in the store, forget about it, they dont even know whats it made of.
I'm sure its not stainless steel cause I've seen alot of rust on it before and it seems it was welded together. The size I need is 3/4.

What would be a better option that doesnt rust, has a high pressure rating and its available in all shapes and sizes?
Somewhere I heard that nickled brass or just brass (dunno witch) holds more pressure than anything else. Dont take my word for this, my memory of it is kinda blurry.
If you know what my solution could be, pls describe a bit how it looks and feels like cause I really dont want to buy the wrong stuff.

...since the store doesnt work on sunday, I can only get these parts tommorow + I got school in the afternoon next week so I have 0 time for my projects and I dont want to wait another week for this so a quick response would be appreciated.

[Gippeto]

3/4" type M copper is RATED for 400psi. 30 bar is 435psi, and I would be comfortable at that.

Joints should ideally be sweated with 95/5 Tin/Antimony solder and a proper flux.

Make certain that the rest of the "package" is up to the task as well.

[FighterAce]

I'm afraid I'm not using copper and I cant afford to... sorry I didnt mention this before
I'm just using metal fittings... knees, Tees and connectors with threads because my air tank is not that big.

If I forgot to tell you anything else please ask

[POLAND_SPUD]

I suggest standard iron pipes and fitting... people have been using them with unregulated propane... 'officialy', they are not rated to high pressures but if you stick to smaller sizes (<=3/4") you should be fine...

Gippeto himself has pressure tested them for us

if you need something rated high you can consider using hydraulic tubing (it's rated really high and comes in a wide range of sizes, though those things are really difficult to find) or hydraulic fittings

[MrCrowley]

I suggest standard iron pipes and fitting... people have been using them with unregulated propane...

That's almost 120PSI

[POLAND_SPUD]

lol I meant CO2

[FighterAce]

120 psi??? I need way more then that... like 400! lol
I have a store not too far from my house and they got all kinds of stuff from nickled brass... at least I think... its kinda yellowish and smooth, no welding marks. Would that hold the pressure better?

I have no idea where to find hydraulic tubing but I need connectors that screw into the fitting with threads. You gotta weld hydraulic tubing and thats no good for me. All I need is a data point on how strong particular materials are and whats the best one to use.
I figured that you guys will have loads of experience with this sort of stuff... was I wrong?

[MrCrowley]

120 psi??? I need way more then that... like 400! lol

He meant unregged CO2, which is up around 800PSI on average.

[FighterAce]

Thats better all I need to do now is find out if they got that... should iron pipes have a rough surface on the inside and welding marks?
Or if it has welding marks that then its not iron?

[c11man]

i have used welded iron pipe and iron fittings (3/4inch) up to 700psi so it will be fine

[FighterAce]

Wow... thats great! I had no idea it could go so high...
Thanks a lot man!

[MrCrowley]

I use it in my hybrid as well, gone up to a 9x mix and if I remember correctly that spiked at over 900PSI on HGDT.

[FighterAce]

Very nice.. Now I see I was greatly underestimating their strength... but they have one disadvantage... rust.
So.. would sanding and painting the inside be enough to prevent it? And if I plan to use ball valves with it, is there a chance that the paint could kinda peel off under the pressure and overtime jam up the ball valve so its having a hard time opening?

[kjjohn]

To avoid rust, you could use galvanized steel fittings. They should be sold in any hardware store that sells black steel or iron fittings. They only cost about 20% more.

Also, don't worry about the pressure in metal pipes. I am currently building a 5x hybrid out of aluminum pipes, which are weaker than steel, and it will be producing up to 700psi upon ignition.

You will definitely be okay with 400.

[POLAND_SPUD]

just buy galvanised version