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# Steam pipe insulation

Member Posts: 16,736
but based on how cool they feel on the outside when the steam is up, I'd say they're fairly close.

All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting

• Member Posts: 52
steam pipe insulation

Is the R-Value of old asbestos pipe covering the same as fiberglass? The asbestos was installed in the late 1920's. Does anyone know the R-value of each?
• Member Posts: 6,928

There was an "R-Value" back then, but it was only a step in the equation to get "U-value".

Corrugated asbestos and magnesia/asbestos both have an internal conductivity value of about 0.5

R = thickness (inches)/internal conductivity

R = 1 / 0.5

= 2.0

So, the old "snowmen" and piping should have an R-value of about 2.0 per inch.

Fiberglass batt insulation claims up to about R 3.7 per inch under ideal circumstance.

• Member Posts: 16,736
Where

did you find that? I don't recall seeing it in any of my Dead Men's books.....

All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting
• Member Posts: 231
R Value of Asbestos

For some reason, I can't find this stated on the web. This might be because nobody measured and/or asbestos came in a few physical forms which had different R values.

There is some published data about the thermal conductivity of asbestos, however, usually given in W/(m*K). You can convert this into R-value per inch (which is usually in (ft^2*F*h)/BTU) as follows:

R value = 1/(6.94 * thermal conductivity)

Where R value and thermal conductivity are in the units described above.

I don't have my CRC or anything with me so I don't know the thermal conductivity for asbestos. However, if you google for "asbestos" and "thermal conductivity", you'll find a few links that show the thermal conductivity. They disagree, of course.

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thrcn.html

Thermal conductivity of 0.17 (after converting units)

R value of 0.9/inch.

http://www.projects.ex.ac.uk/trol/dictunit/notes5.htm

Thermal conductivtiy of 0.2

R value of 0.7/inch

http://www.projects.ex.ac.uk/trol/dictunit/notes5.htm

Thermal conductivity of 0.16

R value of 0.9/inch

http://hypertextbook.com/physics/thermal/conduction/

Thermal conductivity of 0.05 to 0.15

R value of 1.0 to 2.9/inch

http://electron4.phys.utk.edu/141/nov3/November 3.html

Thermal conductivity of 0.084 (after converting units)

R value of 1.7/inch

The interesting result of this exercise (for me) is that the thermal conductivity of asbestos, well, isn't very good. Fiberglass usually has a stated conductivity of 0.04 W/(m*K), which corresponds to an R value of around 3.6/inch. (It would probably be 3.7 if I had more significant digits.)

Perhaps asbestos also offered good radiant resistance (though looking at it, I can't imagine why) or people just liked it 'cause it was easy to apply and/or because it was fireproof. . .

-Michael
• Member Posts: 6,928

From "Mechanical Equipment of Buildings, Volume I", 1916, Harding and Willard.

Got it from Dan's book auction a couple years ago. An absolute gold mine of info.

• Member Posts: 6,928
From the Book Mentioned Below

"The internal resistance of a material is equal to the reciprocal of its so-called internal conductivity (C) multiplied by its thickenss and is represented by the fraction x/C, or 1/Cu, in the case of materials for which the conductivity (or conductance) is given in terms of the construction or thickness stated. For example, the internal resistance of 13 in. of brickwork on the basis of a value of C of 5.0 is 13/5 or 2.6. The internal resistance of 2 in. hollow clay tile based on the value of Cu of 1.14 is 1/1.14 or 0.877."

From the same text: "U = 1/[the sum of] R1 + R2 + Rc"

Since modern "R-value" is the reciprocal of U-value, I believe the "R" in that first equation is the same.

Some common "C-values" for old insulation materials (per inch of thickenss):

Asbestos sheet, 0.29

Asbestos board (corrugated), 0.48

Asbestos wood, 2.70

Asbestos mill board, 0.843

Magnesia board, 0.51

Magnesia (85%) and Asbestos (15%), 0.508

Celotex, 0.34

Corkboard (pure) & Regranulated Cork, 0.3 (avg)

Hair Felts & Hair/Jute blends, 0.26 (avg)

Insulite, 0.34

Masonite, 0.33

Rock Wool, 0.27
• Member Posts: 231
looks right

Looks right in terms of your assumption of where the "R"'s are in your equations. The data I have about the other materials here where published data is still available (rock wool, cork, etc.) comports with what you have there, so this would seem to suggest that the C values given are indeed in the right units for direct conversion to R value.

I guess it just remains to be known whether the stuff they insulated the pipes with was the same R-value. It agrees fairly well (at R=2) with the other stated R-value calculations for asbestos above, which vary from around 0.7 to 2.9/inch.

-Michael
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