STEAM-BOILER INSPECTION, ETC 



STEWART, ROBERT M. 709 



surface 19 by 12 inches, or 228 square inches ; these 

 were the weakest places. The following were the 

 grate and water heating surfaces of the boiler : 



Square feet. 



Grate-surface 791 1 



Heating-surface in furnace '. .' 180 



Heating surface in combustion-chamber and back 



connection 103 



Heating-surface in tubes . 2,171 



Heating surface in uptake 64 



Total heating-surface 2,513 



This boiler had been subjected to an hydrostatic 

 pressure of 60 pounds per square inch, when twelve 

 crow-feet gave way. After being repaired, it was 

 again' subjected to an hydrostatic pressure of 59 pounds 

 per^square inch, which it bore without fracture ; and 

 again to a steam-pressure of 45 pounds per square 

 inch, which it also sustained without fracture. The 

 fuel used in the experiment was wood, and the water- 

 level in the boiler was 15 inches above the highest 

 point of the tubes. When the fire had been brought 

 to steady action, the pressure of the steam gradually 

 increased, commencing with the pressure of 29 i 

 pounds per square inch, to 53i pounds in 13 minutes. 



At the pressure of 50 pounds per square inch, some 

 of the braces in the boiler gave way with a loud report, 

 and when the pressure of 531 pounds was reached, 

 the boiler exploded with terrific violence. The steam- 

 drum and a portion of the shell attached to it, form- 

 ing a mass of about three tons' weight, were hurled 

 to a great height in the air and fell to the earth at 

 about 450 feet from the original position of the boiler, 

 crushing several trees in their fall. Two other large 

 fragments fell at less distances, while smaller ones 

 were thrown much farther. Almost the whole of the 

 boiler was literally torn into shreds, which were scat- 

 tered far and wide, the only portion remaining where 

 the boiler had been, being the tubes. These, though 

 considerably distorted, were otherwise uninjured. 

 Both tube-plates had been blown from the tubes in 

 opposite directions, and at the same moment, for 

 nearly all the tubes were found lying in a heap on 

 the ground immediately beneath the place they had 

 occupied in the boiler, the riveting of their ends over 

 the plates having been simultaneously stripped. The 

 top of the furnace and the top of the combustion- 

 chamber, which, in the boiler, were immediately be- 

 neath the tubes, had entirely disappeared into debris, 

 as _ had also the sides and ends of the shell. The 

 boiler seems to have first yielded by the fracture of 

 the upper row of horizontal braces. The loud report 

 heard, when the pressure attained 50 pounds per 

 square inch, was probablv caused by their breaking. 

 The larger masses were all thrown in one direction 

 at right angles to the side of the boiler; but the 

 smaller fragments were projected radially in all direc- 

 tions, as from a centre. Two heavy bomb-proofs, 

 constructed of large timbers and sand for the protec- 

 tion of the other boilers, were dislodged, and a part 

 of the fence of the enclosure was destroyed by the 

 impact of the flying fragments. The crow-feet, in 

 most cases, remained firmly attached to the shell, 

 and the braces had parted probably the welds 

 leaving the ends still secured to the crow-feet. The 

 screw-bolts which braced the flat water-spaces had 

 slipped from their fastenings in the plate without 

 injury to the screw-threads either upon them or in 

 the plate. The latter was permanently bulged or 

 dished between the bolts, and this stretching of the 

 metal had, by its enlargement of the holes, allowed 

 the screw-ends of the bolts to draw out without in- 

 jury to the threads, either on the bolts or in the 

 plates. 



The ground beneath, and for a considerable dis- 

 tance around where the boiler stood, was saturated 

 with the water of the boiler, in fact made into mud, 

 and the adjacent grass and small shrubbery were so 

 drenched that an ordinary boot was wet through by 

 walking among them. At seven minutes before the 

 explosion took place, the water-gauge on the boiler 



was examined, and found to indicate the water-level 

 15 inches above the top of the tubes. 



The conclusions drawn from this experiment 

 were the following : 



1. An old boiler, containing a large mass of water 

 above the highest point of its heating-surface, can 

 be exploded with such complete destruction as to re- 

 duce it into mere debris, and hurl the fragments in 

 all directions with a force that no ordinary construc- 

 tion of building or vessel could withstand. 



2. That the pressure required for so devastating 

 an explosion is the very moderate one of 53i pounds 

 per square inch. 



3. That with only a wood-fire, generating a far less 

 quantity of heat in equal time than a coal-fire, there 

 were required only thirteen minutes to raise the press- 

 ure from the inspector's working allowance of 30 

 pounds per square inch, to the exploding pressure 

 of 53i pounds per square inch, showing that a few 

 minutes' absence or neglect of the engineer, coupled 

 With an_ overloaded or inoperative safety-valve, are 

 all that is needed to produce the most destructive 

 steam-boiler explosion, even with an old and un- 

 equally-braced boiler, in which it might be supposed 

 a' rupture of the weakest part would precede other 

 fracture, and allow the escape of the pressure without 

 doing further injury. 



4. That in accounting for either the fact of an ex- 

 plosion, or for its destructive effects, there is HO 

 necessity for hypotheses of low water, enormous 

 pressures, instantaneous generations of immense 

 quantities of steam, superheated steam, the formation 

 of hypothetical gases, development of electricity, 

 etc., etc. The most frightful catastrophe can be pro- 

 duced by simply gradually accumulating the pressure 

 of saturated steam to a strain at which the strength 

 of the boiler yields, nor need that pressure be much 

 above what is ordinarily employed with boilers of 

 this type. 



5. That there is no flashing of the boiler-water 

 into steam at the moment of an explosion. On the 

 contrary, with the exception of the small portion of 

 this water vaporized (after the reduction of the press- 

 ure, owing to the rupture of the boiler) by the con- 

 tained heat in it between that due to the temperature 

 of the steams of the exploding pressure and of the 

 atmospheric pressure, it remains unchanged, and is 

 thrown around, drenching the objects near it, and 

 scalding whoever it falls upon. 



6. The weakest portion of the boiler-braces was in 

 their welds. 



V. The equal stretching in all directions of the 

 boiler-plates between the screw-bolts, due to their 

 bulging under the pressure, was sufficient to permit 

 the slipping out of the bolts without injury to the 

 screw-threads either upon them or in the plates. 



8. That this experiment has conclusively disposed 

 of several theories of steam-boiler explosion, re- 

 placing vague conjecture and crude hypothesis with 

 exact experimental facts, and, by thus narrowing the 

 field for the search of truth, has made its discovery 

 more probable. 



These experiments were witnessed by a num- 

 ber of scientific and practical gentlemen con- 

 versant with, and interested in, the construc- 

 tion and application of steam-boilers, and a 

 report was drawn up by B. F. Isherwood, 

 E. S. De Luce, and Sidney Albert, chief engi- 

 neers, U. S. Navy, of which the above are ex- 

 tracts. 



STEWART, ROBERT M., a political leader in 

 Missouri, and former Governor of the State, 

 born in Truxton, Cortland County, N. Y., 

 March 12, 1815 ; died in St. Joseph, Mo., Sep- 

 tember 2i, 1871. When a boy he migrated to 

 Kentucky, and some years later to Missouri, 



