To be added when all the holes are fair and good in the longitudinal seams, but drilled out of place after bending. To be added when all the holes are fair and good in the longitudinal seams, but drilled out of place before bending. To be added when all the holes are fair and good in the longitudinal seams, but punched after bending instead of drilled. To be added when all the holes are fair and good in the longitudinal seams, but punched before bending. To be added when all the holes are not fair and good in the longitudinal seams. To be added if the holes are all fair and good in the circumferential seams, but drilled out of place after bending. To be added if the holes are fair and good in the circumferential seams, but drilled before bending. To be added if the holes are fair and good in the circumferential seams, but punched after bending. To be added if the holes are fair and good in the circumferential seams, but punched before bending. To be added if the holes are not fair and good in the circumferential seams. To be added if double butt straps are not fitted to the longitudinal seams, and the said seams are lap and double riveted. To be added if double butt straps are not fitted to the longitudinal seams, and the said seams are lap and treble riveted. To be added if only single butt straps are fitted to the longitudinal seams, and the said seams are double-riveted. To be added if only single butt straps are fitted to the longitudinal seams and the said seams are treble-riveted. To be added when any description of joint in the To be added if the circumferential seams are fitted To be added if the circumferential seams are lap To be added when the circumferential seams are lap and the strakes of plates are not entirely under or over. .3 W* .4 X* •4 Y++ 1.65 To be added when the boiler is of such a length as to fire from both ends, or is of unusual length, as in the case of flue boilers, and the circumferential seams fitted as described opposite P, R, and S, but of course when the circumferential seams are as described opposite Q and T, V 3 will become V 4. To be added if the seams are not properly crossed. To be added when the iron is in any way doubtful, and the surveyor is not satisfied that it is of the best quality. To be added if the boiler is not open to inspection during the whole period of its construction. Where marked the allowance may be increased still further if the workmanship or material is very doubtful or very unsatisfactory. When the holes are to be rimered or bored out in place, the case should be submitted to the Board as to the reduction or omission of A, B, G, and I as heretofore. When the middle circumferential seams are double-strapped and double-riveted or lap- and treble-riveted, and the calculated strength not less than 65% of the solid plate, S 1 and V 3 may be omitted. The end circumferential seams in such cases should be at least double-riveted. ++ When surveying boilers that have not been open to inspection during construction, the case should be submitted to the Board as to the factors to be used. The strength of ordinary joints is found by the following method :— p = maximum pitch of rivets in inches, provided it does not exceed 10 inches. constant applicable from the following table: C When the work is first class, such pitches may be adopted so far as safety is concerned, yet, in some cases, it may be well not to adopt the greatest pitch found by the formula. The maximum pitch should not, however, exceed 10 inches with the thickest plates for boiler shells. If in any case the pitch is found to exceed that arrived at by the foregoing formula, for the particular description of joint and thickness of plate, such pitches should not be passed, but, in all cases, reported. 2 If the rivets are exposed to double shear, multiply the percentage as found by 1.75. Then take iron as equal to 47,000 lbs.1 per square inch and use the smaller of the two percentages as the strength of the joint, and adopt the factor of safety as found from the preceding scale : { (47,0001× percentage of strength of joint) x twice the thickness of the plate in inches. Inside diameter of the boiler in inches x factor of safety Pressure to be allowed per square inch on the safety valves. (See the Formulæ as given in detail in Appendix to the published Rules.) Riveting Butt Straps, &c.-In the case of ordinary zigzag riveting the strength through the plate diagonally between the rivets is equal to that horizontally between the rivets, when diagonal pitch = 1 horizontal pitch + diameter of rivet. ΤΟ Plates that are drilled in place should be taken apart and the burr taken off, and the holes slightly countersunk from the outside. Butt straps should be cut from plates and not from bars, and should be of as good a quality as the shell plates, and for the longitudinal seams should be cut across the fibre. When the straps are drilled in place they should be taken apart, the burr taken off, and the holes slightly countersunk from the outside. When single butt straps are used they should be one-eighth thicker than the plates they cover. The diameter of the rivets should in no case be less than the thickness of the plates of which the shell is made, but it will be found when the plates are thin, or when lap joints or single butt straps are adopted, that the diameter of the rivets should be in excess of the thickness of the plates. Stays for Dished Ends.-Dished ends, unless of the thickness required for a flat end, should be stayed; but when they are theoretically equal to the pressure needed, when considered as portions of spheres, the stays, when solid, may have a stress of 14,000 lbs. per square inch of net section, but the stress should not exceed 10,000 lbs. when the stays have been welded or worked in the fire, and such stays should be properly distributed. If they are not theoretically equal to the pressure needed they should be stayed as flat surfaces. Hemispherical Ends, Manholes, Doors and Domes.-Hemispherical ends subjected to internal pressure may be allowed double the pressure that is suitable for a cylinder of the same diameter and thickness. The ends should not be formed of less than four pieces. Compensating rings should be fitted around all manholes, and openings of at least the same effective sectional area as the plate cut out, and in no case should the rings be less in thickness than the plates to which they are attached. The openings in the shells of cylindrical boilers should have their shorter axes placed longitudinally. It is very desirable that the compensating rings round openings in flat surfaces be made of L or T iron. Cast-iron doors should not be passed. The neutral part of boiler shells under steam domes should be efficiently stiffened and stayed, as serious accidents have arisen from the want of such precautions. 1 See note, p. 360. Hydraulic Test.-The boilers should be tested by hydraulic pressure to twice the working pressure in the presence, and to the satisfaction, of the Board's Surveyors. Circular Furnaces.-88. Circular furnaces with the longitudinal joints welded or made with a butt strap double-riveted, or double butt straps single-riveted: 90,000 the square of the thickness of the plate in inches working pressure per square inch, provided it does not exceed that found by the following formula : 9,000 × thickness in inches diameter in inches = per square inch. The second formula limits the crushing stress on the material to 4,500 lbs. per sq. in. The length is to be measured between the rings if the furnace is made with rings. If the longitudinal joints instead of being butted are lap-jointed in the ordinary way and double-riveted, then 75,000 should be used instead of 90,000, but where the lap is bevelled and so made as to give the flues the form of a true circle, then 80,000 may be used. When the material or the workmanship is not of the best quality, the constants given above should be reduced, that is to say, the 90,000 will become 80,000; the 80,000 will become 70,000; the 70,000 will become 60,000: when the material and the workmanship are not of the best quality such constants will require to be further reduced, according to circumstances and the judgment of the Surveyor, as in the case of old boilers. One of the conditions of best workmanship is that the joints are either double-riveted with single butt straps, or single-riveted with double butt straps, and the holes drilled after the bending is done and when in place, and the plates afterwards taken apart, the burr on the holes taken off, and the holes slightly countersunk from the outside.1 Cylindrical Superheaters.-89. The strength of the joints of cylindrical superheaters and the factor of safety are found in a similar manner as for cylindrical boilers and steam receivers, but instead of The following examples will serve to show the application of the constants for the different cases that may arise: Furnaces with Butt Joints and Drilled Rivet Holes. 90,000 where the longitudinal seams are welded. 90,000 where the longitudinal seams are double-riveted and fitted with single butt straps. 80,000 where the longitudinal seams are single-riveted and fitted with single butt straps. 90,000 where the longitudinal seams are single-riveted and fitted with double butt straps. Furnaces with Butt Joints and Punched Rivet Holes. 85,000 where the longitudinal seams are double-riveted and fitted with single butt straps. 75,000 where the longitudinal seams are single-riveted and fitted with single butt straps. 85,000 where the longitudinal seams are single-riveted and fitted with double butt straps. using 47,000 lbs. as the tensile strength of iron, 30,000 lbs. is adopted, unless where the heat or flame impinges at, or nearly at, right angles to the plate, then 22,400 lbs. is substituted. When a superheater is constructed with a tube subject to external pressure, the working pressure should be ascertained by the rules given for circular furnaces, but the constants should be reduced as 30 to 47. In all cases the internal steam pipes should be so fitted that the steam in flowing to them will pass over all the plates exposed to the impact of heat or flame. Safety Valve for Superheaters. Superheaters that can be shut off from the main boilers should be fitted with a parliamentary safety valve of sufficient size, but the least size passed without special written authority should be 3 ins. in diameter. The flat ends, &c. of all boilers, as far as the steam space extends, and the ends of superheaters, should be fitted with shield, or baffle, plates where exposed to the hot gases in the uptake. Haystack Boilers.-90. As the uptakes of haystack boilers and others of this type are especially liable to injury from overheating unless careful precautions are taken while steam is being raised, the Surveyor should in all cases endeavour to persuade makers and owners to make the strength of the uptakes considerably in excess of that required for ordinary superheaters subject to external pressure. The employment of Bowling rings is beneficial by adding to the strength as well as allowing for expansion, but if there is a difficulty in getting these fitted, hoops riveted round, although not so desirable as Bowling rings, can be employed to increase the resistance of the tubes against collapse. The use of Bowling rings with a moderate thickness of plate is better than very thick plating. This applies to the uptakes of all boilers of this type, including ordinary vertical donkey boilers. Bowling rings fitted to all such uptakes would be a decided advantage in allowing for expansion. When flaming coal is used extra care is required, and extra strength absolutely necessary. Steel Boilers. 92. The following should guide the Board's Surveyors when the general quality of the steel has been found suitable for marine. boilers. Furnaces with Lapped Joints and Drilled Rivet Holes. 80,000 where the longitudinal seams are double-riveted and bevelled. 75,000 70,000 and not bevelled. 65,000 Furnaces with Lapped Joints and Punched Rivet Holes. 75,000 where the longitudinal seams are double-riveted and bevelled. In the case of upright fire boxes of donkey or similar boilers, 10 % should be deducted from the constant given above, applicable to the respective classes of work. |