Stainless steel tubing for AC lines?

Sailah

Hi,

Wading a bit out of my knowledge zone here. I recently acquired a lot of stainless steel tubing. Like miles of it lol. 1/4"-1" in various wall thicknesses but for example I have a 2200' of 3/8" 0.035" 316/316L Sandvik instrument tubing with lots of accompanying Swagelok fittings.

My thought is that it is completely overkill for the application of plumbing a split AC system I have in a guest house, but suffice to say it was almost free.

I'm not a HVAC expert, nor licensed to perform AC activities. But I am fairly well versed in mechanical things and running, bending, flaring and hooking up lines is well within my wheelhouse. And I like to do things myself.

The AC condenser at this guest house/barn has been in place since the 70's and I would like to retire it. It may run a few weeks in the summer and that's it, I close the place down in the winter.

Good or bad idea?

Thanks!

ChrisJ

For AC my first concern would be cleanliness of the inside of the piping.

Whenever I buy refrigeration grade copper it comes with caps on the ends.

Sailah

Good point. I cannot guarantee the tubing is super clean. Was in a rack stored vertical, 10' pieces. No caps.

Maybe I could steam clean it

Assume it was clean for the sake of argument any reason that stainless steel is a no no for AC?

I would probably end up doing it from copper just due to the fact the lines would need multiple unions to reach the air handler in the attic vs single run of copper tubing.

I am redoing the AC and furnace in my house this fall and those I would be able to do from a single piece so still interested in the topic.

ChrisJ

As far as I know, no.
My antique evaporators are some sort of non-magnetic stainless and they're like new after 83 years inside and out.

Another concern would be pressure ratings especially if dealing with modern refrigerants.

Perhaps @Techman can comment but I'd bet you'd want a working pressure of at least 500 PSI on the liquid line for an R410A system.


A downside is going to be you're going to need to use a flux to braze it. Copper to copper doesn't need an additional flux, just silphos rod.

Sailah

I believe this tubing is rated for 3000 psi.

After doing a little more research I need to stick to steam haha. I think the tubing would be fine but the cleanliness and connection issues seem like they are a showstopper.

But I am thinking about plumbing my shop for air using it!!

ChrisJ

Sailah said:

I believe this tubing is rated for 3000 psi.

After doing a little more research I need to stick to steam haha. I think the tubing would be fine but the cleanliness and connection issues seem like they are a showstopper.

But I am thinking about plumbing my shop for air using it!!

The connection issues IMO is just an inconvenience.
However, the cleanliness would concern me.

A clean system is a happy system which is why flowing nitrogen is a must, regardless of what some claim.

Techman

Hi Gents. There is no problem using SS as far as I know of. How would you make the 90* ells, 45*,couplings,connections to AHU and CU ? You could blow out the SS lengths w/ compressed air,the evacuation will remove any moisture. You could put the LLFilterDrier at the AHU to catch any debris that the compressed air missed ,but I would use a SAE(flare) LLFD for replacing the LLFD if/when needed. And a SuctionLineFD at the AC CU also, to catch the debris ,again. The SLFD might have to be sweat/brazed in at the CU . So, there would have to be some regular ACR copper at the AHU/CU to allow for this, then converted over to the SS.

Is this SS "soft drawn"(bendable,flareable)? Did I make sense? I understand free is free,but is it worth it? Ask away!! Say away!

Sailah

@Techman

Thank you for your thoughts. As should be obvious from my line of questioning I am not a professional. My knowledge is really limited to steam.

I acquired the tubing at auction at a GE Oil & Gas facility for an embarrassingly small sum and have envisioned all sorts of ways to utilize what was assuredly expensive tubing.

The tubing is certainly bendable, I have made all sorts of bends already with my various hand benders. I did attempt a flare but it was not what I would call a good one. The tubing slipped slightly in the flare tool. I managed to make a better one by increasing the clamping pressure.

Having done a little internet research, it appears almost all HVAC and refrigeration connections are brazed is that correct? I understand that the more connections you have the more chances for leaks. My initial thought was to use Swagelok fittings but in terms of absolute sealing, I would think brazing would be a better option. Although Swagelok connections are some of the most trusted in critical high pressure applications.

My guest house has the condenser sitting on a pad, the lines run up the side of the barn to the attic and to the AHU. The vertical run is approx 25'. So I would certainly need to couple at least 2-3 tubes. And the make a 90 across to the AHU of say 20'.

The more I think about this particular application I'm inclined to agree that it is just adding unnecessary complication to what is a time tested solution with copper.

The other application I was considering was to use it in my house AC install. I have a fairly large older house. One side already has AC and fairly new at that. The older main part of the house does not and it gets pretty hot. Coupled with 2 ancient hot air furnaces, it's time to replace them. Presently having the house air gapped, vapor barriered, and well insulated and then basing my heating sizing on some calculations.

But that condenser will be very close to the AHU being a grade placement and AHU in the basement so could probably get away with a 10' stick.

Here's another one of my half baked ideas. 1/4" NPT floor flange installed to overhead floor joists in garage. 3/8" clamp collars. Voila some awesome adjustable shelving for storing machining tools with nicely finished plywood shelves.

Thanks again for your advise.

Sailah

One last little nugget. I just got off the phone with Swagelok as they are sending me material certs for the tubing. I inquired about the absolute integrity and leak proof-ness of their fittings. He assured me that Sandvik tubing and Swagelok, properly installed, would not leak under any circumstances I would put them through.

And ideas on how to test this conclusively? I have plenty of tubing and fittings.

ChrisJ

Sandvik does, and has made fantastic tools for a very long time.
I have a Sandvik hand saw that was my grandfathers.

That's all I can say.

Canucker

Sailah said:

One last little nugget. I just got off the phone with Swagelok as they are sending me material certs for the tubing. I inquired about the absolute integrity and leak proof-ness of their fittings. He assured me that Sandvik tubing and Swagelok, properly installed, would not leak under any circumstances I would put them through.

And ideas on how to test this conclusively? I have plenty of tubing and fittings.

I operate a unit that is piped with 1/4 inch ss lines and swagelok connections. We use it for supercritical reactions to feed CO2 from cylinders at 2000 psi and then gets boosted to 3500-4000 psi in the lines. I haven't had a leak or heard of a burst in those lines yet. I'm willing to bet that it'll take whatever pressure you can throw at it

Sailah

In my mind there is no question that the tubing can take the pressure that I'm sure of. And being 316 stainless it'll last 10 lifetimes. I guess I'm asking is the risk of a tiny leak in what would take multiple fittings to make the connections worth it. If it did leak the service call and subsequent recharge and repipe in copper would far outweigh the benefits now that I've thought about it.

I might be willing to make a shorter run but the AC unit in question would take a lot of fittings to connect.

Thanks for the exercise it's been helpful. I've learned a bit in how these are hooked up which I didn't quite understand when I posed the question this morning.

Canucker

The lines were put together by an engineer, so there are a lot of fittings used in the 20+ ft of line. (Must have had a box of fittings when he put it together) Haven't had a leak in any of those either. I would think that as long as the connections are done properly, you could have as many as you like and there wouldn't be a problem.

bob_46

I have used thousands of Swagelok fittings and have never seen a bad one. Be sure you cut it square and deburr it inside and out.
Make sure there are NO scratches on the outside of the tube, if there are polish it with crocus cloth. Stick the tube in the fitting until it bottoms, mark the nut with a marker and tighten it one and a quarter turns (don't guess) done. We used Swagelok Real-Cool-Snoop to leak test.

ChrisJ

@Sailah Sounds like you're project may be falling into place beautifully.

KC_Jones

The company I work for is installing Swagelok fittings on one of our new prepackaged refrigeration systems. These are large ammonia refrigeration packages (10-100 tons). We have zero issues with them. Very high quality fittings if you use them I wouldn't worry at all.

Harvey Ramer

You may want to research the expansion rate of SS and make sure to incorporate that into piping design. It can become a major factor in long straight runs. Especially with rigid tubing.