CR4® - The Engineer's Place for News and Discussion®


Previous in Forum: Deep Sea Highway   Next in Forum: Cooling Technology
Close
Close
Close
13 comments
Participant

Join Date: Jul 2017
Posts: 2

Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 12:21 PM

First post. After searching the site I find it necessary to ask my questions.

I am trying to determine how copper tubing and brass fittings will be affected when used at 250* - 300* F and 150 PSI max pressure in an air compressor application. All the information I find, including that found in the copper pipe handbook, references fluids and/or steam capacities. My compressor is currently plumbed with 3/8" copper tubing and what appear to be iron flare fittings between the pump and the tank. I am in the process of installing an aftercooler (Stacked plate transmission oil cooler) between the pump and the tank and need to know if brass fare fittings will suffice. The data I find for brass fittings rates them at a max operating temperature of 250* F. I expect, but have yet to confirm, that pipe and fitting temperature could climb to 300* F with prolonged use. Copper and brass (non-corroding) are chosen to prevent debris from clogging the small passages in the oil cooler.

- Is the load placed on the plumbing system different with compressed air vs pressurized fluid?

- WILL the brass fittings and copper pipe fail if temperatures reach 300* F for 10 - 20 min?

- is there a non-corroding alternative to copper and brass?

Thank you

Emil

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 19288
Good Answers: 1129
#1

Re: Pressure and Temperature rating differences for gas and fluid in copper pipe?

07/12/2017 12:27 PM

You not only need to comply with safety ratings, but also safety margins...Stainless steel may be the way to go...

https://northerncal.swagelok.com/blog/bid/101340/faq-what-is-the-temperature-rating-of-a-swagelok-tube-fitting

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply Score 1 for Good Answer
Guru

Join Date: Apr 2010
Posts: 5759
Good Answers: 577
#2

Re: Pressure and Temperature rating differences for gas and fluid in copper pipe?

07/12/2017 12:48 PM

If the fittings are rated at 250F, I would not exceed that.

The load should be the same with pressurized gas or fluid. Force equals pressure times area. The amount of volume expansion would be much greater for a gas or a liquid which changes to a gas upon release of pressure.

Register to Reply
Guru

Join Date: Apr 2009
Location: USA, Florida
Posts: 1464
Good Answers: 115
#3

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 2:27 PM

I routinely work with pressure piping systems between 300 and 2200 psi.

I would highly recommend stainless steel tubing with stainless steel compression fittings.

One caveat, many stainless steel compression fittings are permanent (once applied, they can't be removed without cutting them off).

__________________
An obstacle is something you see when you take your eyes off the goal.
Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9559
Good Answers: 456
#4

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 4:05 PM

Just a note on nomenclature - air, steam and water are all fluids.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Register to Reply Score 1 for Good Answer
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#5
In reply to #4

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 4:39 PM

The primary cause of failure you should concern yourself with is ductile failure.

Brass and copper both begin increasing ductility in the temperature range above rated service temperature. I would not recommend copper/brass at these temperatures.

Stainless steel is the berries for this application you have in mind.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26715
Good Answers: 701
#6
In reply to #4

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 6:23 PM

Quite.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
3
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8399
Good Answers: 771
#7

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/12/2017 11:21 PM

Well to go against the ideal grain here I have seen countless commercial air compressors that used copper and brass for the plumbing right off the heads going either to the tank or cooler assy.

My 15 HP shop air compressor uses brass fittings and copper line. Same with several other smaller ones (1 - 10 HP) I have as well and I know for a fact when ran hard they will top 300F discharge temperatures at the first fitting coming of the heads.

I've also built custom compressors from various salvaged and surplus components and I have by default used brass fitting and copper line and never had a problem with it.

At worst after the first time or two things have been ran hot the fitting may need tightening though. Brass and copper compression and flare fittings tend to relax and settle in after the first few heat cycles.

Register to Reply Good Answer (Score 3)
Power-User

Join Date: Nov 2008
Location: Seoul, Republic of Korea
Posts: 288
Good Answers: 26
#8

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/13/2017 1:26 AM

I think I find myself with tcmtech here in general response to your post.

To address your questions

Pressure / Temp ratings for piping systems apply for all services - gases, liquids, steams. So even if compressed air is not mentioned the limits are the same. The one caveat I'd offer is that liquids are more dense so although it does not impact the pressure rating the supports for the piping need to be stronger but that is not relevant to your case.

It depends on the pressure. Ratings for piping, tubing and fittings is usually in a table of temp v pressure. At lower temps the same item is good at a higher pressure. So when you run the compressor harder (I assume this means more flow) do you still get the 150psi? If not what is the pressure limit at 300F?

The timing issue is difficult to judge. You need to allow time for the fitting to heat up to 300F and that is a finger in the air calculation. Even when at the higher temp I think the failure mechanism is ductile failure which takes time. Even if it does not fail it might weaken the fitting- ie as fitting stretches and melds it thins the walls.

This is just air? So the only corrosive component is water I think? I guess it depends where you take the water out (if you do)? Some of the new plastics are good for this sort of service!

__________________
Free advice guaranteed or your money back
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#9
In reply to #8

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/13/2017 9:22 AM

I suspect that at 300 F, air with water vapor entrained is non-corrosive. On the other hand, if it cools down sufficiently for condensate to form (between running cycles??), then some corrosion might be expected by the interaction of carbonated condensate on copper, with less effect on brass.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: May 2016
Posts: 884
Good Answers: 41
#10

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/13/2017 10:47 AM

Bottom line, design the system to work with the operating conditions. I'd go with stainless myself. I've blown out fittings and it's no fun. It's noisy and scary.

Realize that copper and brass have no endurance limit and eventually the fittings will fatigue at a sharp corner if you are loaded to near or beyond the rating of the fitting. It's not a question of whether it will break, but rather a question of when. In most cases the rated life of the fitting is statistically far enough out there if you stay in the limits, but when you push or exceed the limits, the expected failure life comes in close enough to be of concern.

Is the compressor two stage? If so, you could put an intercooler between stages and drop the output temperature of the second stage to within the fitting limits, but it is still likely to be cheaper to just use stainless on the output.

Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13569
Good Answers: 155
#11
In reply to #10

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/13/2017 1:35 PM

Another plus: An intercooler saves big bucks in the short and long run.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Participant

Join Date: Jul 2017
Posts: 2
#12

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/13/2017 1:51 PM

The compressor is a single stage, 3 HP, 60 gal, vertical, 11.3 CFM @ 90 PSI, 135 PSI Max unit. It is a split 2 piston design with about 12" of spiral finned 3/8" copper tubing between the outlet of piston 1 and the "T" fitting at the outlet of piston 2. From the "T" fitting at piston 2, there is a ~24" x 3/8" spiral finned copper tube going to an elbow and into the check valve at the tank. My interest in the aftercooler is to remove as much moisture from the air charge before it hits the tank and also to take advantage of the increased air density, about 38% if the temp drop is 200+ F.

I would like to thank all the respondents so far.

Emil

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26715
Good Answers: 701
#13
In reply to #12

Re: Pressure and Temperature Rating Differences for Gas and Fluid in Copper Pipe?

07/14/2017 3:11 AM

There is another thread running about removing moisture, this time from biogas, on here at the moment. Might be worth adding it as a subscribed favourite, perhaps?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Register to Reply 13 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Evil_Fiz (1); James Stewart (3); JohnDG (1); Jpfalt (1); PWSlack (2); Rixter (1); simonsd (1); SolarEagle (1); tcmtech (1); WJMFIRE (1)

Previous in Forum: Deep Sea Highway   Next in Forum: Cooling Technology

Advertisement