Copper vs Steel boiler components

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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DetroiTug
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Copper vs Steel boiler components

Post by DetroiTug » Fri Feb 10, 2017 1:01 am

This topic often comes up over which is better. I finally took the time to run some tests today and the conclusion was, there is little difference.



-Ron
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Re: Copper vs Steel boiler components

Post by cyberbadger » Fri Feb 10, 2017 2:11 am

Double posted from Froya new boiler thread....

Ron,

I saw your test on the youtubes...

I think the gauge having heat from the copper/brass test influenced the steel test.

The bourdon tube in the gauge probably could hold as much water as the "boiler"/pipe in your test.
-CB

P.S. I like the video and use of stopwatch and ir temp gun. Science is good.
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Re: Copper vs Steel boiler components

Post by DetroiTug » Fri Feb 10, 2017 3:50 am

I started a new thread as we had highjacked the other, apologies for that Froya.

The gauge was a few degrees warmer for the steel test, but not very much and I doubt it had much effect on the outcome. We waited a while until the gauge cooled off.

Going to run the same test again in the next few days and use 15ml of water and see what happens. Just talked to one of my steam friends that said he doesn't believe it :lol:

-Ron
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Re: Copper vs Steel boiler components

Post by cyberbadger » Fri Feb 10, 2017 6:22 am

I thought this was relevant...

Evaporative Power of Brass, Copper, and Iron Boiler Tubes
A late number of the London Mechanics' Magazine contains an article on the above important question, by W. G. Tosh, from a paper read by him before the Institution of Mechanical Engineers at Manchester, England. He constructed small vertical boilers of equal dimensions, and placed in the center of each a single tube, two inches in diameter; and of No. 14 wire gage thickness. A gas flame was applied to each tube—iron, brass, and copper —successively, during a certain period of time, which was equivalent to the same quantity of fuel consumed in each case. The experiments were first conducted during the day, then at night, at times when there was little probability of a change of pressure in gas pipes. Eight of these were made with the boilers, and the quantity of water evaporated was measured by the number of inches it was lowered in a boiler by each experiment. The result was in favor of the greater evaporating power of the brass over the iron tubes, in the proportion of 125 to 100 ; that is, two pounds or two tuns of coal, or other fuel, will, with the use of brass tubes in a boiler, evaporate twenty-five per cent more water than iron tubes with tho same quantity of fuel, under precisely the same circumstances. In the same proportion that brass surpassed iron in evaporative power, copper was found to surpass brass. The evaporative powers, relatively, of the three metals in tubes for steam boilers, he found were as follows: Iron, 100 ; brass, 125; copper, 156. The experiments of Mr. Tosh were subjected to a searching criticism by the engineers of the Institution, and strong doubts were expressed as to their correctness. We give the results, in substance, as wo find them, and enjoin some of our correspondents to make similar experiments, because it is a question of vast importance. If it be true that copper tubes in boilers will evaporate fifty per cent more water than iron tubes, no other kind of tubes should be employed, and no steam boiler should be constructed without copper tubes. In our opinion, too high an evaporative value was obtained both for brass and copper over iron; but this is a question which experiment alone can settle, and the sooner this is done correctly, so much the better for mechanical science. It takes the pressure of 150,000 lbs. to punch an inch hole in an iron plate one inch thick.
https://books.google.com/books?id=8hdAA ... 22&f=false

-CB
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Re: Copper vs Steel boiler components

Post by DetroiTug » Fri Feb 10, 2017 11:11 am

Andy,

That's a good find. It reads "a gas flame was applied to each", doesn't mention if it was the same burner. A simple burr in an orifice, different air/fuel mixture or added restriction in the piping can alter the BTU output of seemingly identical gas burners.

Also: "We give the results, in substance, as wo find them, and enjoin some of our correspondents to make similar experiments, because it is a question of vast importance."

Apparently many have over the last hundred and some years and arrived at differing results, according to Fred, modern steam power plants do not favor one material over the other for heat transfer. If there were dollars to be saved by increasing production at a rate of 156/100 by using copper, that is all they would use where capable.

I knew he was right about it, I just ran those tests to remove any doubts I had. I'm still learning.

It's not a difficult test to run, set up your own and have a go at it.

-Ron
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Re: Copper vs Steel boiler components

Post by RGSP » Fri Feb 10, 2017 12:22 pm

Copper was the original choice for boilers in England because good quality metal was available in thin sheets whereas iron (not steel in the early days) was not, and in any case was more variable. As things went on, steel started to be available but of dubious quality, but got better, and by the turn of the 20th Century, almost all boiler drums were made of steel, and rivetted - welding not yet being up to it. Copper was still used for some tubes and some fireboxes: given lowish temperatures and pressures, it was less liable to water and flue-gas induced corrosion, and had a longer life, but at more expense.

Railway and Steamship companies started to do comparisons between copper and steel tubed boilers about then, with results sometimes favouring one, and sometimes the other: in truth, doing a precise quantitative measurement of heat input to a boiler isn't easy, and any differences were within experimental error. Amateur "enthusiasts" polarised into steel-loving and copper-loving camps, with scant regard for precise science - a bit like petrol heads comparing different cars after a few beers these days.

Fireboxes were always difficult things to make, and even after good, quality controlled, steel became available, copper continued in use by many railway companies, often associated with the water chemical content in their respective areas. The manufacturing issue is a big one though: a skilled copper-smith can more-or-less build a complete fireboxe on his own, using nothing but wooden patterns, hammers, dollies, and hand drills. The size of press, and the complex press tools needed to get steel sheets to the required shape, meant that a great deal more investment was needed, and using red-hot rivets inside a firebox was always a horrible job, and still is.

The difference between then (first quarter of 20th Century) and now is mainly in welding technology, and closely related, quality control in steels which means they CAN be welded safely. If welding can be used to fabricate fireboxes, it changes the game, and of course steam pressures (and temperatures) have increased to the point where copper is no longer safe, although may still be used for historic boilers.

Things are different on the model scale at reduced temperatures and pressures, but in full scale boilers, even fairly small ones, the heat transfer differences between thin steel tubes and slightly thicker coppers ones are hardly measureable, and certainly not measureable with a bit of soot on the surfaces of both, and a little muck and scale on the inside. Copper tubes may still last longer, but we in the UK are strongly discouraged from using them, because even with a small boiler running at 100 psi max, temperatures can occasionally go over the specified limits for copper, and most, if not all, insurance companies will not accept copper in NEW boilers.

The choice now, I suppose, is really between copper and cunifer. The latter has substantially better high temperature propeties than copper, and is much more corrosion resistant than most boiler steels, but in the steamboat world we don't yet have much experience of using it, although it has been the metal of choice in many small/medium industrial boilers for a few decades. I don't claim to be able to point to the best alloy composition for cunifer, but people are settling in to using one or two standards. The alloy phonon scattering in cunifer makes its heat transfer properties substantially worse than the best copper, which means that the choice between steel and cunifer is not at all to do with heat transfer, and everything to do with cost, corrosion resistance and life.

Incidentally, I'm more expert in the electrical conductivity properties of copper than the (related) thermal ones, but to get the best electrical conductivity figures quoted in text books, the copper needs to be of the "OFHC" grade: in other words oxygen free high conductivity. It also needs to be fully annealed and not work-hardened. Standard copper has a resistivity which is still low, but usually several times higher than the OFHC stuff. Another factor is that milling or lathe work with the OFHC is guaranteed to produce blue air surrounding inexperienced machine tool operators: it's very soft, and very sticky, and is inclined to produce enormous burrs, which are horribly liable to cut hands etc. because the material has been work-hardened.

Metallurgy is a complicated subject!
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Re: Copper vs Steel boiler components

Post by fredrosse » Fri Feb 10, 2017 12:32 pm

Ron, I have taken the relevant information from the previous posts (New VFT boiler for Frøya) and repeated it here. Note that tests to investigate the performance of heat transfer can often give misleading results, unless strict controls on everything are implemented. Your testing is well done, however there are some areas of the tests that may introduce additional variables which influence the conclusions, but do not exactly match the conditions of a fired boiler continuously producing steam. I believe the following text tells the Copper vs Steel story very accurately, so I have added it to this thread, I know, rather long and boring, but I am an engineer nerd....

I can say with great certainty there is virtually no difference in heat transfer if Copper vs. Steel tubes are used in a steam boiler. I have worked as a professional engineer in the heat transfer, fluid mechanics, and thermodynamics arena for nearly 45 years, and, at least in these realms, I know the real technology.

I have checked some numbers, using data from my steamboat VFT boiler, which has 48 tubes, steel, 1.25 inch outside diameter x 0.095 wall, 18 inches long. (31.75mm outside diameter x 2.41mm wall, 457mm long), with total heat transfer surface area of 20 square ft (1.85 M^2). About 75% of the tube length is submerged in boiling water, 25% is above the water.

Considering the heat transfer in the boiling water submerged portion of the tubes, If the tubes were changed from carbon steel to commercial copper, heat transfer in the submerged tubes would go up from 62075 BTU per hour, to 62112 BTU per hour (18.193 kW to 18.204 kW), this is very very small increase.


A very reasonable analogy can often make this more clear. Let us say we are having a traveling race, having three separate segments, for 9 miles total distance.

The first 3 miles of the race is done with brisk walking, on foot only,
The second segment is using any motor vehicle you like, and is also 3 miles distant.
The third segment for the remainder of the race, again three miles, and you use a good horse.

In this analogy, the first segment of the race, on foot, represents the travel of heat from the flue gas to the surface of the tubes, and this process is by far the greatest resistance to travel, at 3 MPH, taking about 60 minutes time.

The second segment of the race, with any motor vehicle, say a Ford Pinto, or a new Corvette. This represents the travel of heat through the tube metal, Steel tubes (Ford Pinto) or Copper Tubes (Corvette). This process, takes 3 minutes for the Ford, at 60 MPH, and only 1 minute with the Corvette at 180 MPH.

The third segment of the race, with a thoroughbred horse, represents the travel of heat from the tube surface into the boiling water, a traveling method far faster than walking, but much slower than the automobile, say 30 MPH taking 6 minutes to complete.

So in this travel race, the entire three segment trip with the Ford Pinto takes 69 minutes, and with the Corvette 67 minutes. While the Corvette is wildly faster than the Ford Pinto, the overall trip time is virtually no different. Yes, the Copper tubes do make better heat transfer, but not in any way significantly.
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Re: Copper vs Steel boiler components

Post by cyberbadger » Fri Feb 10, 2017 6:43 pm

I am willing to take a crack at this test - but to make it fair - can someone give me the correct alloy I need to represent 1.25" firetubes in both copper. I need the alloy and the wall thickness that would be acceptable for an ASME code boiler.

I have the steel spec from Nyitra's boiler - 1.25" Boiler Tube, SA-178 Gr A 0.105" wall.

Now how do I source this...

Mcmaster only has these that are close to the size
General Purpose Low-Carbon Steel
Easy-to-Weld 4130 Alloy Steel

Online Metals has:
DOM Mild Steel Tube A513 TYPE 5 (Drawn Over Mandrel)

-CB
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Re: Copper vs Steel boiler components

Post by DetroiTug » Fri Feb 10, 2017 9:23 pm

Andy,

I've purchased A-178 steel boiler flue from this place.

Wolverine Boiler Tube Sales  
Address: 12405 Churchill Rd, Rives Junction, MI 49277
Phone: (517) 589-8271
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Re: Copper vs Steel boiler components

Post by cyberbadger » Sat Feb 11, 2017 5:01 am

Ron,

I just think they would probably laugh at me. I only need 1 tube.... :(

Fred - which would be a comparable specced copper tube?

-CB
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