RULE II.-BOILERS AND ATTACHMENTS. Section. Boilers to have eight inches space between bottom of boiler and woodwork.. 21 Boilers, auxiliary, for seagoing steamers. 25 Boilers, coil and pipe, inspection of 39 Boilers, space required at back end of. 23 Boilers, used for other than marine purposes not allowed.... 37 Boilers, tubular, vertical.. 18 Boiler, heads bumped, concave, and flat, strength of. 17 Boiler head, flat, with stiffening plate, pressure on. 6 Boiler heads, Western rivers, thickness of.. 17 Braces and stays, strains allowed (iron). 6 Braces and stays, strains allowed (steel). 7 Braces for flat surfaces, strength of. 5 Butt straps, thickness of... 3 Copper steam pipes, flanging of.. 38 Feed-water, temperature of. 16 Furnace shell, top of, to be same thickness as cylindrical shell. 7 Furnaces, vertical boiler, pressure on.. 15 Flues, riveted and lap-welded. 8 Flues, thickness of material required when not otherwise specially provided for. 9 Flues, lap-welded, not exceeding 6 inches diameter, length of. 10 Flues, lap-welded, exceeding 6 inches and not exceeding 16 inches diameter, when not required to be made in sections. 11 Flues, lap-welded and riveted, when, may be allowed in 5-foot sections 12 Flues, riveted and lap-welded, exceeding 6 inches and not exceeding 40 inches diameter, carrying excess of steam provided in section 8.. 13 Flues, thickness of material, lap-welded. 9 Flues, corrugated, extra.. 14 Flues, ribbed. 14 Flues, thickness of material, for furnaces. 15 Gauge cocks, number of, and how to be inserted. 27 Gauges, low-water, in use prior to February 28, 1872 31 Gauges, low-water, for horizontal cylindrical boilers. 34 Gauges, steam, kind admissible... 29 Gauges, low-water, guard to prevent getting into steam pipe 32 Gauges, to record steam pressure correctly, to be attached.. 30 Holes cut in bilge or bottom to be accessible. 38 Holes cut in boiler to be strengthened 38 Huston type brace, strain allowable on Heads of drums, tubulous boilers, construction of. 39 Manholes, dimensions of 21 Plate containing certain data to be attached to boilers........ 24 Plugs of Banca tin, how inserted... 26 Section. Pressure, hydrostatic, proportion applied to steam pressure allowed... 4 Pressure, hydrostatic, how applied to boilers with steam chimneys.. 33 Pressure, steam, how to determine 3 Pressure for boilers built prior to February 28, 1872. 1 Pressure for boilers built after February 28, 1872. 2 Pressure allowed boilers built ten years, how determined.. 1 Rivet holes must be fairly drilled 2,3 Safety valves, construction and attachment of. 28 Safety valves on donkey boilers.... 28 Shell plates to be rolled to form of shell with grain of material 7 Slip joints, material constructed of, for salt-water steamers. 23 Steam and mud drums 17 Steam chimneys, construction of 15 Stopcock on feed pipe... 38 Valves, etc., when to be of brass 38 Woodwork near boilers internally heated, space required 20 Woodwork near boilers externally heated, space required... 19 Woodwork and other ignitible substances near boilers, pro tection to.. 22 (1) PRESSURE ALLOWABLE ON BOILERS OF VARIOUS DIMENSIONS BUILT PRIOR TO FEBRUARY 28, 1872. 1. Boilers built prior to February 28, 1872, shall be deemed to have a tensile strength of 50,000 pounds to the sectional square inch, whether stamped or not, and shall be tested under the rule prescribed for boilers inspected under the provisions of section 36 of the act relating to boilers built after the 28th of February, 1872. Any boiler having been in use ten years or more shall, at the first annual inspection thereafter, be drilled at points near the water line, and at bottom of shell of boiler, or such other points as the local inspectors may direct, to determine the thickness of such material at those points, and the general condition of such boiler or boilers at the time of such inspection; and the thickness of said material shall be determined thereafter at such annual inspection as the local inspector may deem necessary, and the steam pressure allowed shall be governed by such ascertained thickness and general condition of the boiler. (See table of pressures allowable on boilers made since February 28, 1872.) 2. In the first column to the left will be found the diameter of boilers varying by 2'' from 36'' to 48"' and by 6'' from 48"' to 96"'. In the second column will be found the thickness of boiler plates, expressed in the decimal parts of an inch, and varying-by Too" nearly-from it to $"; .1875, 25, .3125, and .375 are the decimal equivalents for id', ", "', and '. The decimals .21, .23, .26, and .29 correspond nearly to 18", 1", 13", and " in the table of the pressures allowable on boilers made prior to February 28, 1872. At the heads of the double columns will be found the tensile strength of the plates per square inch of section ; also one-sixth (b) of that amount. The pressures allowable on single-riveted boilers will be found in the first divisions of the double columns under the tensile strength and opposite the diameters and thickness; and in the second divisions the pressures allowable on boilers where all the rivet holes have been fairly drilled instead of punched and the longitudinal laps of their cylindrical parts double riveted. 3. The pressure for any dimension of boilers not found in the table annexed to these rules must be ascertained by the following rule, viz: Multiply one-sixth (b) of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thicknessexpressed in inches or parts of an inch-of the thinnest plate in the same cylindrical shell, and divide by the radius or half diame. ter-also expressed in inches-and the sum will be the pressure allowable per square inch of surface for single riveting, to which add 20 per cent for double riveting, when all the holes have been “fairly drilled” and no part of such hole has been punched. Where butt straps are used in the construction of marine boilers, the straps for single butt strapping shall in no case be less than the thickness of the shell plates; and where double butt straps are used, the thickness of each shall in no case be less than five-eighths (4) the thickness of the shell plates. 4. The hydrostatic pressure applied must be in the proportion of 150 pounds to the square inch to 100 pounds to the square inch of the steam pressure allowed. 5. Where flat surfaces exist, the inspector must satisfy himself that the spacing and distance apart of the bracing and all other parts of the boiler are so arranged that all will be of not less strength than the shell, and he must also, after applying the hydrostatic test, thoroughly examine every part of the boiler. 6. No braces or stays* hereafter employed in the construction of boilers shall be allowed a greater strain than six thousand (6.000) pounds per square inch of section, and no solid or hollow * To determine diameter of circular brace or stay to withstand a given stress, divide the stress by the product of .7854 by the stress allowed per square inch of section (see sections 6 and 7, Rule II), and extract the square root of the quotient. Example: Given pressure on stay equal 4,500 pounds, on material allowed 6,000 pounds per square inch of section, then 4,500 Diameter = .98 inch. 6,000 X .7854 screw stay bolt shall be allowed to be used in the construction of marine boilers in which salt water is used to generate steam, unless said screw stay bolt is protected by a socket. But such screw stay bolts without socket may be used in staying the fire boxes and furnaces of such boilers and elsewhere when fresh water is used for generating steam in said boilers. Water used from a surface condenser shall be deemed fresh water. The flat surface at back connection or back end of boilers may be stayed by the use of a tube, the ends of which being expanded in holes in each sheet beaded and further secured by a bolt passing through the tube and secured by a nut. An allowance of steam shall be given from the outside diameter of pipe. For instance, if the pipe used be 14 inches diameter outside, with a 17-inch bolt through it, the allowance will be the same as if a 11-inch bolt were used in lieu of the pipe and bolt. And no brace or stay bolt used in a marine boiler will be allowed to be placed more than 104 inches from center to center on fire boxes, furnaces, and back connections ; nor on these than at a greater distance than will be determined by the following formulas : The working pressure allowed on flat surfaces fitted with screw stay bolts and nuts, or plain bolt with single nut and socket, or riveted head and socket, will be determined by the following rule: When plates de inch thick and under are used in the construction of marine boilers, using 112 as a constant, multiply this by the square of the thickness of plate in sixteenths of an inch. Divide this product by the square of the pitch or distance from center to center of stay bolt. EXAMPLE. 16 Plate 16 inch thick with socket bolts or stay, 6-inch center, would be 112, the constant, multiplied by the square of 7, the thickness of the plates in sixteenths, which is 49, would give 5,488, which, divided by the square of 6, which is 36, being the distance from center to center of stays or the pitch, would be 152, the working pressure allowed, provided the strain on stay or bolt does not exceed 6,000 pounds per square inch of section. Plates 4 inch thick, stay bolts spaced 4-inch center> 112 x 16 =112 pounds W. P. 112 x 25 Plates in inch thick, stay bolts spaced 5-inch center= 25 112 pounds W. P. Plates i inch thick, stay bolts spaced 6-inch center= 112 x 25 =77. 36 pounds W. P. 112 X 36 Plates & inch thick, stay bolts spaced 6-inch center= =112 36 pour W. P. Plates above 7 inch thick, the pressure will be determined by the same rule, excepting the constant will be 120; then a plate inch thick, stays spaced 7 inches from center, would be as follows: 120, the constant, multiplied by 64, the square of thickness in sixteenths of an inch, equals 7,680, which, divided by the square of 7 inches (distance from center to center of stays), which is 49, would give 156 pounds W.P. Plates for 1% of an inch thick, spaced 104 inches, would be On other flat surfaces there may be used stay bolts with ends threaded, having nuts on same, both on the outside and inside of plates. The working pressure allowed would be as follows: A constant 140, multiplied by the square of the thickness of plate in sixteenths of an inch, this product divided by the pitch or distance of bolts from center to center, squared, gives working pressure. EXAMPLE. A plate | inch thick, supported by bolts 14 inches, would be 140 x 144 =102 pounds W.P. Same thickness of plate, with bolts 12-inch centers, would be 140 x 144 =140 pounds W.P. Flat part of boiler-head plates when braced with bolts having double nuts and a washer at least one-half the thickness of head, where washers are riveted to the outside of the head, and of a size equal to of the pitch of stay bolts, or where heads have a stiffening plate covering the area braced will equal the thickness of head and washers, the head and stiffening plate being riveted together, with rivets spaced and of sufficient sectional area of rivets as determined by section 6, Rule II, for socket bolts shall be allowed a constant of 200, rivets to be spaced by thickness of washer on the stiffening plate. Boiler heads so reinforced will be allowed a thickness to compute pressure allowed of 80 per cent of the combined thickness of head and washer, or head and stiffening plate. EXAMPLE. A plate inch thick, with a washer & inch thick and 5.6 inches square, supported by bolts 14-inch centers, would be 200 X 144 = 146 pounds W.P. 196 Spaced 15-inch centers, with a washer & inch thick and 6 inches square, supported by bolts 15-inch centers, would be 200 X 144 =128 pounds W.P. 225 |