“The outside surfaces of the end plate in the vicinity of the furnace fronts are a great source of trouble in some boilers, particularly where plane furnaces are fitted and flush rivets used for connecting them to the end shell plates.
“The insides of the furnaces and combustion boxes next require attention. The most common defects here are lamination of the furnace plate (if of iron), slight collapsing of furnaces, wasting of the furnace plates (particularly when anthracite coal has been used), and wasting when the fire bar bearers or bridges have rested against the plate.
“In the combustion box the buckling of flat plates may have occurred; plates may have wasted from leaks, distortion of the crown sheet from shortness of water may have occurred, or tubes may leak, and whenever, after sounding with the hammer, doubt exists as to the strength of the plate, a hole should be drilled through to test the thickness.
“The wing sides of the furnace may next be examined (through the usual peep holes or by having a boiler mounting taken off for the purpose), and the shell plating on the sides of the boiler, paying special attention to the plates where the feed water enters.
“We may next examine the outside of the bottom of the boiler, which should never be totally inaccessible to the eye, and should always be capable of being reached by a long-handled paint brush, for if kept well painted, the bottom of the boiler is, so far as the exterior is concerned, as durable as the other parts of the shell.
“If, however, the bottom is not kept painted and gets damp, and more particularly from bilge water, it will corrode rapidly, and the boiler must be lifted for examination. Under these circumstances a new boiler must at five years, at the very most, be lifted for examination, and if found comparatively good it should not be taken as an indication of the probable condition of any other boiler working under similar conditions, for the only means of avoiding a great risk in this matter is to rigidly inspect.
“In the case of flat bottomed boilers in small vessels a good result has obtained by placing them on a bed of cement, which if properly done excludes the bilge water from approaching the plate; but even this precaution would scarcely be sufficient to justify an engineer in neglecting to lift the boiler at reasonable periods for examination of the bottom.
“The internal examination of the boiler is continued from the top by examining the stays in the steam space, the tube and tube plates, getting down between the nests of tubes and reaching the crowns of the furnaces. The surface of the shell plates should also be examined, more particularly if the boiler contains plates subject to heat on the outside and steam on the other (as in the case of wet up take boilers), for under these conditions a steel plate may become as weak and unreliable as a piece of cast iron.
“If the boiler is fitted with the superheater, the examination of the latter is of the utmost importance, as rapid destruction is here a common occurrence. In the case of a circular marine boiler of any size, nothing need be taken for granted, even though an hydraulic test be made up to twice the working pressure, because there is room for a thorough internal inspection which may disclose defects that would not be shown from the hydraulic test. The proper proportions of fire grate surface, heating surface, steam space, etc., in a marine boiler differ with the type of boiler and engine, and the steam pressure and degree of expansion employed.
“Upon the question of steam space, for example, it is asserted by many that marine boilers are not so liable to prime under the higher pressures, and as a result of this asserted fact the steam receiver is in some cases being dispensed with.