THE REPAIR OF BOILER TUBES.[10]
The tubes of tubular boilers must, for different reasons, be taken out when the generator has worked for a certain length of time. Such a necessity presents itself when the extremities of the tubes are worn out and can no longer be fastened with sufficient tightness into the plate, or when the portion of the tube in contact with water is so incrusted that there results a notable diminution in the production of steam, or when the tubes exhibit local injuries, or, finally, when the interior of the boiler must be examined.
REPAIR OF BOILER TUBES.
This latter contingency arises for every boiler after a period of from 6 to 8 years, and it requires the removal of all the tubes. It furnishes an occasion to remedy the other defects, that would have of themselves required the renewal of only a certain number of the tubes. In the interval between these thorough inspections defects may present themselves which require the removal of a certain number of tubes. The frequency of such repairs depends upon the nature of the feed water, upon the quality of the fuel, upon the pressure at which the generator operates, upon the state of repair in which the boiler is kept, and naturally also upon the quality of the metal of which the tubes themselves are composed.
Selenitic water deposits in the long run a very hard and adhesive incrustation, which acts as an obstacle to the transmission of heat.
The more calcareous waters fill the intervals between the tubes with deposits which can be but partially removed by the washing of the boiler, and which often form a calcareous mass such as to prevent all circulation of water around the tubes.
In both cases the tubes are heated beyond measure, elongate, detach themselves from the tube-plates, and burn in places, or lose enough of their resistance to allow them to become flattened by the pressure of the steam.
The loosening of the tubes likewise acts injuriously upon the plates, which the pressure causes to bend outwardly. The result is that the tubes may become completely detached.
Sulphurous fuel corrodes the extremities of the tubes near the fire-box and also notably attacks the hind extremities, in the interior, against the tube-plate. It likewise renders brittle those tubes whose metal is bad, so that they split either of themselves or at the least effort made to tighten them up in the tube-plate.