Steam, Its Generation and Use

by Babcock & Wilcox Company

[TABLE 64] RADIATION FROM COVERED AND UNCOVERED STEAM PIPES CALCULATED FOR 160 POUNDS PRESSURE AND 60 DEGREES TEMPERATURE Pipe Inches Thickness of Covering 1⁄2 inch 3⁄4 inch 1 inch 11⁄4 inch 11⁄2 inch Bare 2 B. t. u. per lineal foot per hour 149 118 99 86 79 597 B. t. u. per square foot per hour 240 190 161 138 127 959 B. t. u. per square foot per hour per one degree difference in temperature .770 .613 .519 .445 .410 3.198 4 B. t. u. per lineal foot per hour 247 193 160 139 123 1085 B. t. u. per square foot per hour 210 164 136 118 104 921 B. t. u. per square foot per hour per one degree difference in temperature .677 .592 .439 .381 .335 2.970 6 B. t. u. per lineal foot per hour 352 269 221 190 167 1555 B. t. u. per square foot per hour 203 155 127 110 96 897 B. t. u. per square foot per hour per one degree difference in temperature .655 .500 .410 .355 .310 2.89 8 B. t. u. per lineal foot per hour 443 337 276 235 207 1994 B. t. u. per square foot per hour 196 149 122 104 92 883 B. t. u. per square foot per hour per one degree difference in temperature .632 .481 .394 .335 .297 2.85 10 B. t. u. per lineal foot per hour 549 416 337 287 250 2468 B. t. u. per square foot per hour 195 148 120 102 89 877 B. t. u. per square foot per hour per one degree difference in temperature .629 .477 .387 .329 .287 2.83

Covering—Magnesia, canvas covered.

For calculating radiation for pressure and temperature other than 160 pounds, and 60 degrees, use B. t. u. figures for one degree difference.

Radiation from Pipes—The evils of the presence of condensed steam in piping systems have been thoroughly discussed above and in some of the previous articles. [Pg 315] Condensation resulting from radiation, while it cannot be wholly obviated, can, by proper installation, be greatly reduced.

Bare pipe will radiate approximately 3 B. t. u. per hour per square foot of exposed surface per one degree of difference in temperature between the steam contained and the external air. This figure may be reduced to from 0.3 to 0.4 B. t. u. for the same conditions by a 1½ inch insulating covering. [Table 64] gives the radiation losses for bare and covered pipes with different thicknesses of magnesia covering.

[TABLE 65] APPROXIMATE EFFICIENCIES OF VARIOUS COVERINGS REFERRED TO BARE PIPES Covering Efficiency Asbestocel 76.8 Gast’s Air Cell 74.4 Asbesto Sponge Felt 85.0 Magnesia 83.5 Asbestos Navy Brand 82.0 Asbesto Sponge Hair 86.0 Asbestos Fire Felt 73.5

Many experiments have been made as to the relative efficiencies of different kinds of covering. [Table 65] gives some approximately relative figures based on one inch covering from experiments by Paulding, Jacobus, Brill and others.

Based on one-inch covering.

The following suggestions may be of service:

Exposed radiating surfaces of all pipes, all high pressure steam flanges, valve bodies and fittings, heaters and separators, should be covered with non-conducting material wherever such covering will improve plant economy. All main steam lines, engine and boiler branches, should be covered with 2 inches of 85 per cent carbonate of magnesia or the equivalent. Other lines may be covered with one inch of the same material. All covering should be sectional in form and large surfaces should be covered with blocks, except where such material would be difficult to install, in which case plastic material should be used. In the case of flanges the covering should be tapered back from the flange in order that the bolts may be removed.