Surface Inspection.—Rivets must be true to form, free from scale, fins, seams and all other unsightly or injurious defects.
In view of the fact that the government is using many hundred tons of these rivets, shown by the records of the tests to be vastly superior to any iron rivet made, in all the essentials of a good rivet, it would seem that it would benefit the boiler maker, the purchaser of the boiler and also the maker of the rivet by adopting a standard steel rivet to be used in all steel boilers.
BRACING OF STEAM BOILERS.
The material of a boiler being satisfactory and the plates being thoroughly and skillfully riveted there remains the important matter of strengthening the boiler against the enormous internal pressure not altogether provided for.
Fig. 42.
To illustrate the importance of attention to this point it may be remarked that a boiler eighteen feet in length by five feet in diameter, with 40 four-inch tubes, under a head of 80 pounds of steam, has a pressure of nearly 113 tons on each head, 1,625 tons on the shell and 4,333 tons on the tubes, making a total of 6,184 tons on the whole of the exposed surfaces.
Not only is this immense force to be withstood, but owing to the fact that the boiler grows weak with age—a safety factor of six has been adopted by inspectors, i.e., the boiler must be made six times as strong as needed in every day working practice.
