“When an examination is to be made inside and outside of a boiler, the boiler must be properly prepared for the same, which may be done as follows:
“The tubes should be swept; the furnace cleaned out; the fire bars should be taken out; the bridges in the furnace should be taken down; the up take smoke box and combustion box should be cleaned out and swept; every man hole and hand hole or peep hole door should be removed; the bottom of the boiler should be cleaned out and dried (in damp weather a little heat may be necessary for this purpose); all impediments, if any, should be removed in order to allow the bottom outside to be inspected; at the time of inspection a few mats, good lights, a hand hammer and small chipping hammer should be at hand. In the case of a boiler having any plates weakened by corrosion, a 5⁄8 inch tapping drill with a drilling brace should also be provided to test the thickness of such plates if considered necessary.
“The safety valves should invariably be taken out for examination, and it is a commendable feature sometimes followed to take out the feed valves, stop valves, blow off and brine cocks; at the same time, all the deposits that would prevent a thorough examination of the boiler should be removed. In some cases, however, there may not be time for the scaling before it is necessary for the repairs to be gone on with, and, in that case, a good examination may with care be made by an experienced man.
“To proceed, then, with the examination, the boiler should be entered through the man hole door beneath the furnaces, examining the boiler bottom and the bottom and sides of the furnaces all the way along, and on arriving at the end of the boiler the water space and stays at the backs of the combustion boxes can be examined as well as the midship combustion box stays and plates. In an old and corroded boiler it may be found necessary to use a chipping hammer very freely about the furnaces, particularly below the lap of the furnace.
“The most corroded part of a furnace will generally be found about on a line with the fire bars, but the furnaces may have suffered from some other cause than the corrosion due to ordinary wear, as, for example, from chemical or galvanic action, and in that case they may be found comparatively good at the sides but with the extreme bottoms in a dangerously corroded state, perhaps in the form of pit holes extending half through the plate and hidden by a coating of red scale, which requires to be chipped away before the pit holes are brought to light.
“Corrosion by galvanic action may have produced honey combing or a general attack over the surfaces, which have a dark or dark and sparkling appearance, the latter more particularly when corrosive action has been very active.
“Of these various classes of corrosion that which is the most deceiving is that which attacks the plates over the largest surface of the plate, leaving at the same time an apparently smooth exterior surface, for in this case the extent of the waste cannot be so clearly detected by the eye, and the only reliable way of testing the thickness is by drilling a hole through the plate.
“The flanges of the furnaces should always be examined in the bends, for flaws, for such defects, although not very common, do at times unexpectedly make their appearance, and might, if not detected, be the means of breaking the boiler down at sea. This part of the inspection being made, any drilling that is to be done to ascertain the thickness of suspected plates may be proceeded with before the rest of the inspection is made.
“It may, however, be well to remark that a very common defect is the wasting away of the combustion box plates around the necks of the stays or the internal surface of the plates, and it is a usual thing for deposits to accumulate around these necks, hence, unless these deposits have been removed (particularly in the case of boilers about three years old), the true condition of the boiler may not be known.
“The plate around the man hole door should next be examined, a great defect from waste at the surface that makes the water tight joint. Next comes the man hole door itself, which should have the rubber or other material used to make the joint cleaned off, for cases have occurred where the surface beneath was found apparently sound, whereas the application of a chisel showed that the iron was so corroded that but little iron was left in the flange, causing great surprise that the whole door had not blown out. This defect may generally be looked for in old boilers, and serves to emphasize the necessity for strong wrought iron doors.