First Aid to Locomotive-Type Boilers.
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By T. C. Aveling, Assoc.M.Inst.C.E.
On page 162 of your .issue of October 25th appears an interesting article on " Repairs to Steam Wagon Boilers," and its contributor describes minutely the actual work of a boilermaker in repairing a locomotive-type boiler. Without depreciating the value of such an article in the hands of a skilled workman, the few notes, herewith, may be read with the previous article, and. may, perhaps, appeal to users of locomotive-type boilers who have, merely, had driving or using experience, and no actual former experience of the upkeep of this type of steam producer. Let the unskilled endeavour to carry out the instructions of the above-mentioned article, and irretrievable damage might be done to the boiler in question : my object is to supplement it with one addressed to the unskilled and inexperienced, and, moreover, to advise an owner to obtain, when repairs are necessary, the services of a boilermaker who is accustomed to this class of work, rather than to allow his driver to try his 'prentice hand on carrying out the repairs enumerated so clearly by "'Engineer-in-charge."
Wear and Tear.
To keep ycelr boiler in good condition, cleanliness is the first law. If a rivet leaks, or if any other leakage takes place, attention. should be given to it immediately, and this should be carried out by a competent locomotive boilermaker. Boilers should be cleaned out at least once a fortnight ; all covers should be removed and fire-bars drawn, the tubes and fire-box swept with a hard broom, and any accumulated ashes removed, as there is a strong possibility that local oorrosion will be set up from the contact of these ashes with the plate. The riveted heads of the screw-stays, the heads of the crown stay-bolts, and all seams and joints, should be examined. The. safety plug should be drawn and cleaned, and all scale removed from the end of the plug which is in contact with the water. The supporting brackets for the fire-bars should be examined, and the seam between the foundation ring and the fire-box sides carefully inspected for leakage.
Externally, inspection should be made round the mudholes, blow-off tap, water-gauge fitting, and any joints in connection with the boiler ; also, round the liners in betweel the horn-plates, crown-plates, and riveted slay-heads. If a joint is leaking it should, immediately, be re-Made. The smoke-box tube-plate should be carefully examined for "wasting," which may he set up through priming or even by the admission of rain down the funnel. Tube ends shoul
be examined, as these will deteriorate from the same cause, The joints between the cylinders and the holler should be watched, and, in examining the tube-piates, all oxidation., rust, etc., should be cleared away between the tubes and the bottom flange. In fitting the safety plug, tallow should be applied internally to the thread. In the country, a force pump should be used for washing out the boiler; in towns, the main supply, if head is sufficient. The hose should enter at the man-hole, and the boiler should be well swilled out, the refuse being allowed to run out of the mud-holes. If the scale is thick, a slight tapping of the stay-heads, internally and externally, and of the plates, will cause this deposit to leave the surface of the fire-box. A scaling slice should be entered through the man-hole, and the scale on the crown el lire-box removed ; next, short rakes of flat iron, or copper, should he introduced through the mud-hole door, and the mud and loose scale removed.
Too much attention cannot be given to internal cleanliness, as the accumulation of scale is a frequent cause of bulging and burning of the plates, in addition to concealing any wasting of the plates which may have been set up through defective feed water.
Feed Water.
The purest water should, always, be used. Grease, oil, or bran, which are often recommended for leaking tubes, should not be allowed to enter the feed tank or boiler. A very moderate use of common soda will, in many cases, counteract the action of impurities in the water.
Re-making Joints.
The jointing surface of the plates should be scraped, carefully, and all red lead removed. Grummets, of tar yarn, should be made to fit the covers, and the joint should be covered with a mixture of red and white lead in the proportion of one to two. When raising steam, as the holler warms, these joints should be carefully gone over with a spanner, to take up any slackness caused by the softening of the joint by the heat.
Blow.-off Tap.
The blow-off tap should be used, daily, as this is the first and best preventive of scale. The tap should be opened, when the engine is at rest, with, say, a pressure of 5o1b. on the gauge, the boiler not making steam. The sediment is, by these means, allowed to settle to the lowest part of the boiler, and is swept out by the rush of escaping steam and water. The blow-off tap should be rotated in one direction, to prevent ridges forming on barrel and plug.
Gauge Fittings.
The screwed plug opposite the supply hole should be withdrawn every cleaning Lime, and the deposit removed with a piece of wire or small drill, otherwise these become choked and show a false water level. Taps should be kept in working condition, and gauges blown through at least three times a day.
Safety Valves.
These should be frequently removed and cleaned : the screws and pins must be kept in free working condition, care being taken to test them every day.
Leaky Tubes.
If a tube should burst or leak, never drive a taper plug into the ends as a permanent repair. A new tube should be fitted at the .earliest opportunity, and at once if possible.
Depreciation of Boilers.
This takes place : first, from external corrosion ; second, from infernal corrosion ; third, from overheating of plates, and corrosion in the fire-box.
External Corrosion.—One of the greatest evils occurs in the shell barrel, and this cannot be detected. The lagging conceals the plates, upon which the action due to leakages from joints, and rain lodgments, are gradually having effect : the moisture is, thus, brought into con tact with the plate, forming a ferric oxide scale, and this process, when it occurs frequently, eats the plate away by its deeper and deeper oxidation. To prevent this, the lagging should be removed at least every two years. A leaky pump gland will have as detrimental an effect as a leaky joint, and, round the blow-off tap, corrosion is often set up through leakage, whilst, in some cases, the tap has had to be removed and replaced on another part of the box, owing to carelessness over the watching of this joint. The same remarks apply to the inlet tap of the injector. Internal Corrosion.—This is often caused by impure feed water. Bad feed water has a general wasting effect on all the plates, and evidence of this appears, sometimes, in large blotches on the plates, and again in the form of pitting of the plates. When internal corrosion appears, from the abovs cause, change of water is beneficial. Local corrosion may appear, too, on the shell, at the water-line, or at the bottom of the shell, or the fire-box alone may be affected, owing to the great affinity the destructive agent has, apparently, for the hottest surface.
Grooving comes under the heading of corrosion, though, at its commencement, it is a mechanical defect. It is found, generally, in the old types of boilers, at the underlap of the shell longitudinal seams, on the fire-box and fire-box casing plates, and at the edge of the foundation ring. The cause of grooving is the contraction and expansion of the plates, the metal, thereby, becoming fatigued, and, each time, more susceptible to the action of a destructive agent. Overheating.
The corrosion of a lire-box is found at the fire-bar level, round the heads of the riveted screw-stays, at the underlap of the vertical seams, and between the tubes at the fire-box tube plate. The first-mentioned of these is, generally, caused by the use of coke, which gives off a large proportion t)f carbonic acid gas. The combustion of both coal and coke results, also, in the formation of steam in small proportions, setting up local corrosion of the plates at bar level.
Corrosion on round stays is due to leakage, and the grooving of the tube-plate arises from the same cause. The effect of deposit exposed to the heated gases of the fire depends upon its thickness and non-conducting properties. This deposit prevents the heat from being taken up readily by the water, and it is, for this reason, liable to cause such overheating of the plates as to make them unfit to sustain the pressure.
The Effect of Grease.
Munroe (on boilers, page 29) states that the Board of Trade has found the majority of explosions of this type of boiler to be caused by longitudinal grooving in the shell, the tendency of the plate being to take a truly cylindrical shape. But if, in the first instance, the shell has not been truly cylindrical this process continues, and grooving is set up. In the present method of the manufacture of the shell, the longitudinal seams are butt-jointed and above water level, thus doing away with one of the most likely causes of explosion.
Laying Aside Engine.
Remove mud and man-hole covers, and keep the engine in a dry situation. Wash out and examine plates and mountings, before re-filling for work. In frosty weather, special precaution should be taken as regards the water in the boiler during the night. Shut the water-gauge taps, empty the glass tubes, and drain the steam-gauge connection. Examine the feed pipes, and the injector connection before starting. It is well, when working next day, to keep a fire in all the night, if frost is likely; but, before leaving, carefully note that all steam and water connections are not leaking, in order to prevent lowering of the water level, and consequent overheating of plates.
j.We feel that Mr. Aveling's article, as much as the previous one on other aspects of repairs to motor-wagon boilers, cannot help but be useful to many of our readers. The two, read in conjunction, convey numerous practical hints. Whether a driver who is not a boilermaker can do the jobs, depends, obviously, upon the care he exercises, and his aptitude. We have known excellent work to be done by socalled " unskilled " drivers.--Eo.1