half inch in thickness shall show a reduction of not less than forty-five (45) per cent. Provided, however, That steel plate required for repairs to boilers built previous to April 1, 1886, may be used for such repairs when showing a contraction of area of not less than forty (40) per cent. 7. In the following table will be found the width-expressed in hundredths of an inch-that will equal, near enough for practical purposes, one-quarter of one square inch of section of the various thicknesses of boiler plates: 8. The gauge to be employed by inspectors to determine the thickness of boiler-plates, and the widths in the table, will be any standard American gauge furnished by the Treasury Department.* 9. All samples intended to be tested on the Riehlè, Fairbanks, or other reliable testing-machine, must be prepared in form, according to the following diagram, viz., eight inches in length, two inches in width, cut out at their centres in the manner indicated: * Inspectors may make requisition on the Department for the necessary supply of certificates for their own use, and blank affidavits for the use of boiler manufactures. 10. All tests made of boiler material must be recorded upon a table of the following form: Tensile tests of samples of material intended to be employed in the construction of boilers of steam-vessels made on -testing-machine. 17 21 19 33 14 6 RULE II.-BOILERS AND ATTACHMENTS. Boilers to have eight inches space between bottom of boiler and wood work................... Boilers, auxiliary, for sea-going steamers... Boilers, space required at back end of............... Boilers used for other than marine purposes not allowed........... Boilers, tubular, vertical......... .. ..................... Braces and stays, strain allowed. .......... Braces, for flat surfaces, strength of............................ Flues, thickness of material, riveted.... ........... .............. ......... Flues, thickness of material, lap-welded................................ Flues, thickness of material, over 16 inches in diameter................ Flues, corrugated, extra................................................... ................. Flues, thickness of material, for furnaces................ Gauge-cocks, number of, and how to be inserted....... Gauges, low-water, in use prior to February 28, 1872........ Gauges, low-water, for horizontal cylindrical boilers...... Gauges, steam, kind admissible.......... Gauges, low-water, guard to prevent getting into steam-pipe........ Plate containing certain data to be attached to boilers............................... Plugs of Banca tin, how inserted................... ........................... .................. .......... Pressure, hydrostatic, for western towing and freight steamers. Pressure for boilers built prior to February 28, 1872......... Pressure, what constitutes high...... Safety-valves, construction and attachment of..... Safety-valves on donkey-boilers... Slip-joints, material constructed of, for salt-water steamers..... Stand-pipes, construction of............ Wood-work near boilers internally heated, space required...... 31 4 29 32 1 13 24 24 19 19 16 Wood-work near boilers externally heated, space required......... ........ 15 18 (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 50,0fi0 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. (See table of pressures allowable on boilers made since February 28, 1872.) 2 48 489 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 3" nearly-from" to 3"; .1875, .25, .3125, and .375 are the decimal equivalents for 6", ", fe", 5 and g". The decimals .21, .23, .26, and .29 correspond nearly to 18", 11′′, 13′′, and 1" 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 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 thicknesses; 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 (1) of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thickness-expressed in inches or parts of an inch-of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter-also expressed in inches—and the sum will be the pressure allowable per square inch of surface for singleriveting, to which add twenty per centum for double-riveting. 4. The hydrostatic pressure applied must be in proportion of one hundred and fifty lbs. to the square inch to one hundred lbs. to the square inch of the steam pressure allowed. 5. Where flat surfaces exist, the inspector must satisfy himself that the bracing and all other parts of the boiler are of equal strength with 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) lbs. per square inch of section, and no screw stay bolt shall be allowed to be used in the construction of marine boilers in which salt water is used to generate steam. But such screw stay bolts may be used in staying the fire-boxes and furnaces of such boilers, and not elsewhere, when fresh water is used for generating steam in said boilers. 7. Plates of iron or steel, used in the construction of boilers, extending beyond the cylindrical shell to the front of the boiler over the furnaces, shall extend at least 12 inches below the centre of the shell, and shall not be of less tensile strength or thickness than the adjoining sheets in the cylindrical portions of the shell. RIVETED FLUES. 8. Flues having a diameter of from 6 inches to 7 inches shall have a thickness of material of not less than .18 of an inch, and if, in the opinion of the inspectors, it is deemed safe, be allowed a steam pressure, according to the thickness of material, as follows: Thickness of material, .18, .19, .20, .21. Pressure in lbs., 189, 194, 199, 204. Flues having a diameter of over 7 inches, and not over 8 inches, shall have a thickness of material of not less than .20 of an inch, and if, in the opinion of the inspectors, it is deemed safe, may be allowed a steam pressure, according to the thickness of the material, as follows: Thickness of material, .20, .21, .22, .23, .24. Pressure in lbs., 184, 189, 194, 199, 204. Flues having a diameter over 8 inches, and not over 9 inches, shall have a thickness of material of not less than .21 of an inch, and if, in the opinion of the inspectors, it is deemed safe, may be allowed a steam pressure, according to the thickness of material, as follows: Thickness of material, .21, .22, .23, .24, .25, .26. Pressure in pounds, 179, 184, 189, 194, 199, 204. Flues having a diameter over 9 inches, and not over 10 inches, shall have a thickness of material of not less than .21 of an inch, and if, in the opinion of the inspectors, it is deemed safe, may be allowed a steam pressure according to the thickness of material, as follows: Thickness of material, .21, .22, .23, .24, .25, .26, .27. Pressure in pounds, 174, 179, 184, 189, 194, 199, 204. Flues having a diameter over 10 inches, and not over 11 inches, shall have a thickness of material of not less than .22 of an inch, and if, in the opinion of the inspectors, it shall be deemed safe, may be allowed a steam pressure, according to the thickness of material, as follows: Thickness of material, .22, .23, .24, .25, .26, .27, .28, .29. Pressure in pounds, 169, 174, 179, 184, 189, 194, 199, 204. Flues having a diameter over 11 inches, and not over 12 inches, shall have a thickness of material of not less than .22 of an inch, and if, in the opinion of the inspectors, it is deemed safe, may be allowed a steam pressure, according to the thickness of material, as follows: Thickness of material, .22, .23, .24, .25, .26, .27, 28, 29, .30. Pressure in pounds, 164, 169, 174, 179, 184, 189, 194, 199, 204. Flues having a diameter over 12 inches, and not over 13 inches, shall have a thickness of material of not less than .23 of an inch, and if, in the opinion of the inspectors, it shall be deemed safe, may be allowed a steam pressure, according to the thickness of material, as follows: Thickness of material, .23, .24, .25, .26, .27, .28, .29, .30, .31, 32. Pressure in pounds, 159, 164, 169, 174, 179, 184, 189, 194, 199, 204. Flues having a diameter over 13 inches, and not over 14 inches, shall have a thickness of material of not less than .24 of an inch, and if, in the opinion of the inspectors, it is deemed safe, may be allowed a steam pressure, according to the thickness of material, as follows: |