Note.
Probably one-quarter, if not one-third, of all boiler-work is done in the way of repairs, hence the advice of men who have had long experience in the trade is the one safe thing to follow for the avoidance of danger and greater losses, and for the best results the united opinion of 1, the engineer, experienced in his own boiler and 2, the boiler-maker with his wider observation and 3, the owner of the steam plant, all of whom are most interested.
Corrosion is a trouble from which few if any boilers escape. The principal causes of external corrosion arise from undue exposure to the weather, improper setting, or possibly damp brick work, leakage consequent upon faulty construction, or negligence on the part of those having them in charge.
Internal corrosion maybe divided into ordinary corroding, or rusting and pitting. Ordinary corrosion is sometimes uniform through a large portion of the boiler, but is often found in isolated patches which have been difficult to account for. Pitting is still more capricious in the location of its attack; it may be described as a series of holes often running into each other in lines and patches, eaten into the surface of the iron to a depth sometimes of one-quarter of an inch. Pitting is the more dangerous form of corrosion, and the dangers are increased when its existence is hidden beneath a coating of scale. There is another form of decay in boilers known as grooving; it may be described as surface cracking of iron, caused by its expansion and contraction, under the influence of differing temperatures. It is attributable generally to the too great rigidity of the parts of the boiler affected, and it may be looked upon as resulting from faulty construction.
Fig. 69.
In plugging a leaky tube with a pine plug, make a small hole, of 3⁄16 of an inch diameter, or less, running through it from end to end. These plugs should never have a taper of more than 1⁄8 of an inch to the foot. It is well to have a few plugs always on hand. [Fig. 69] exhibits the best shape for the wooden plug.
QUESTIONS
BY THE PROPRIETOR TO THE ENGINEER IN CHARGE, RELATING TO CONDITION OF THE BOILER,
How long since you were inside your boiler?
Were any of the braces slack?
Were any of the pins out of the braces?
Did all the braces ring alike?
Did not some of them sound like a fiddle-string?
Did you notice any scale on flues or crown sheet?
If you did, when do you intend to remove it?
Have you noticed any evidence of bulging in the fire-box plates?
Do you know of any leaky socket bolts?
Are any of the flange joints leaking?
Will your safety-valve blow off itself, or does it stick a little sometimes?
Are there any globe valves between the safety-valve and the boiler? They should be taken out at once, if there are.
Are there any defective plates anywhere about your boiler?
Is the boiler so set that you can inspect every part of it when necessary?
If not, how can you tell in what condition the plates are?
Are not some of the lower courses of tubes or flues in your boiler choked with soot or ashes?
Do you absolutely know, of your own knowledge, that your boiler is in safe and economical working order, or do you merely suppose it is?
QUESTIONS
ASKED OF A CANDIDATE FOR A MARINE LICENSE RELATING TO DEFECTS IN BOILER WITH ANSWERS.
If you find a thin plate, what would you do?
Put a patch on.
Would you put it on inside or outside?
Inside.
Why so?
Because the action that has weakened the plate will then act on the patch, and when this is worn it can be replaced; but the plate remains as we found it.
If the patch were put on the outside, the action would still be on the plate, which would in time be worn through, then the pressure of the steam would force the water between the plate and the patch, and so corrode it; and during a jerk or extra pressure, the patch might be blown off.
It is on the same principle that mud-hole doors are on the inside.
If you found several thin places, what would you do?
Patch each, and reduce the pressure.
If you found a blistered plate?
Put a patch on the fire side.
If you found a plate at the bottom buckled?
Put a stay through the centre of the buckle.
If you found several?
Stay each, and reduce the pressure.
The crown of the furnace down?
Put a stay through the middle, and a dog across the top.
If a length of the crown were down, put a series of stays and dogs.
A cracked plate?
Drill a hole at each end of the crack; caulk the crack, or put a patch over it.
If the water in the boiler is suffered to get too low, what may be the consequence?
Burn the top of the combustion chamber and the tubes; perhaps cause an explosion.
If suffered to get too high?
Cause priming; perhaps cause the breaking of the cylinder covers.