Maxims and Instructions for the Boiler Room / Useful to Engineers, Firemen & Mechanics; Relating to Steam Generators, Pumps, Appliances, Steam Heating, Practical Plumbing, etc.

by N. Hawkins

4. Divide product 2 by product 3, and the result is the number of braces, required for the head.

Table No. 1 gives the total area in square inches. No. 2, areas to be braced. No. 3, number of braces of one inch round iron required, allowing seven thousand five hundred pounds per square inch of section at one hundred pounds steam pressure.

Table No. 3 will be found of more practical use than Table 2, for it gives directly the number of braces required in any given boiler, instead of the area to be braced. It was calculated from Table 2. The iron used in braces will safely stand a continuous pull of 7,500 pounds to the square inch, which is the figure used in computing the foregoing table. A round brace an inch in diameter has a sectional area of .7854 of an inch, and the strain that it will safely withstand is found by multiplying .7854 by 7,500, which gives 5,890 pounds as the safe working strain on a brace of one-inch round iron.

In a 60-inch boiler, whose upper tubes are 28 inches below the shell, the area to be braced is, according to table 2, 930 square inches. If the pressure at which it is to be run is 100 pounds to the square inch, the entire pressure on the area to be braced will be 93,000 pounds, and this is the strain that must be withstood by the braces. As one brace of inch-round iron will safely stand 5,890 pounds, the boiler will need as many braces as 5,890 is contained in 93,000, which is 15.8. That is, 16 braces will be required. The table is made out on the basis of 100 lbs. pressure to the square inch, because that is a very convenient number.

Table No. 1. TOTAL AREA ABOVE TUBES OR FLUES.

(Square Inches.)

Height from tubes to shell.	DIAMETER OF BOILER IN INCHES.
	36	42	48	54	60	66	72
15	389
16	419
17	458	526
18		566	620	667
19		608	667	720
20		650	714	770	824
21			756	824	882
22			808	878	937
23				930	996	1059
24				982	1056	1121
25				1037	1116	1184
26				1090	1209	1252	1324
27				1145	1234	1316	1394
28					1291	1381	1465
29					1352	1445	1536
30					1414	1511	1608
31						1576	1674
32						1641	1746
33							1818
34							1896

Table 2. AREAS TO BE BRACED. (Square Inches.)

Height from tubes to shell.	DIAMETER OF BOILER IN INCHES.
	36	42	48	54	60	66	72
15	206
16	235
17	264	297
18		331	365	396
19		316	404	439
20		401	444	483	519
21			485	528	568
22			526	574	618
23				620	668	714
24				667	720	769
25				714	772	825
26				761	824	882	937
27				809	877	940	998
28					930	998	1061
29					983	1056	1124
30					1037	1115	1187
31						1174	1252
32						1234	1317
33							1382
34							1447