Chapter 2 Firetube Boilers Flashcards
1-What would cause a fire tube to burst or explode?
Fire tubes are normally under external pressure They may collapse but do not burst.
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2-What boiler has a crown sheet that is braced similarly to the locomotive crown sheet.
The scotch marine boiler SM
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3-What internally fired boiler frequently has more than one furnace?
The scotch marine or the scotch dry back often has two to four circular furnaces when the boiler is of larger diameter.
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4-How are internal furnaces braced?
If flat, they are stay-bolted. If circular, they may be thick enough to self supporting for moderate pressures. If they are not thick enough, they may be stay bolted, corrugated , or braced by Adamson rings.
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5-If used, where should fusible plug be located in any boiler?
Not lower than the lowest safe water level.
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6-What is the minimum thickness required for a steel boiler tube in order that a fusible plug may be installed?
0.22 inches page chapter 2
What are the maximum pressure and temperature allowed on copper tubes or nipples in fire tube boilers?
250 psi and 450 degrees F page chapter 2
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7-What fusible metal is used in fire actuated fusible plugs? What is its required melting point?
Tin 445-450 degrees F page chapter 2
8-state the reason for beading the ends of tubes of fire tube boilers?
Beading increases the holding power of the tubes and eliminates to a large degree the burning and erosion of tube ends. Therefore, beaded tube ends are used in fire tube boilers.
State the reason for flaring the ends os tubes of water tube boilers?
Flaring of tube ends increases the holding power of the tubes. Since fire is not in contact with a water tube end, tubes in water tube boilers are usually flared.
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9-Explain the meaning of externally and internally fired boilers.
Externally fired boilers have a separate furnace built outside the boiler shell. The HRT boiler is probably the most widely known example of the externally fired boiler.
In internally fired boilers, the furnace forms and integral part of the boiler structure, the VT, locomotive firebox, and the scotch marine are well known examples of internally fired boilers.
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10-Where are stay bolts most likely to break in the locomotive firebox boiler?
Usually the top row of stay bolts and the first row of radial stays, with fracture occurring close to the inner surface of the outer sheet(wrapper sheet)this area is a high heat zone, causing large expansion and contractive movements.
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11-What are the most common staying methods used on an HRT boiler?
Four methods are used
-Through stays are used below the tubes because there is insufficient room for other stays, which would accumulate deposits more readily.
-Diagonal stays are used above the tubes to support the flat, unstayed tube sheets above the tubes.
-Gussets stays are used above the tubes.
-If not over 36 in. diameter and not over 100 psi, structural shapes can be used if they are arranged according to ASME code requirements.
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12-Name three causes of bagging(bulging) of the shell on an HRT boiler.
-Oil (from lubricated pumps rods, ect) getting into the boiler feedwater and being carried to the lower part of the shell, which is exposed to the fire, and thus causing overheating
-Scale or mud (from sediment in the water) deposits on the lower portion of the shell, restricting heat transfer.
-Excessively localized flame on a portion of the shell, causing overheating
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13-How are tubes holes made per code requirements?
They are punched to not over ½ in. less than finished diameter and finished by machining. They are often cut with a pilot drill and rotating cutter.
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14-How much larger than a fire tube may the tube hole be?
1/16 inch in diameter page 47 chapter 2
How much larger for a water tube?
1/32 inch in diameter. Page 86 chapter 3
15-How are the ends of shell plates and butt straps formed for the longitudinal seam?
They should be formed by rolling or pressing and not by blows.
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16-How far through the sheets should the ends of stay bolts extend before they are riveted over?
Not less than two threads.
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17-Why should the feed water not discharge into the water leg?
The cooling action of the water against the hot furnace sheets would cause serious stress and probable damage.
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18-What purpose do smokebox doors serve in a locomotive boiler?
Inspection, cleaning, and tube replacement.
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19-Name four types of firing-door construction in a VT boiler?
Flanged together and riveted, flanged together and butt welded, both sheet flanged out and riveted(sucker-mouth) and riveted doorframe ring.
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20-What are four types of VT boilers?
Standard straight-shell, Manning, tapered-shell, and submerged head.
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21-What are the reasons for or advantages in the deviations from the standard type of the other types named in the answer above?
The submerged head protests the upper end of the tubes from over heating.
The Manning and tapered shell types allow a larger grate area and furnace volume.
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22-On what point of construction is the maximum allowable pressure based in the standard VT boiler?
On the ability of the shell or furnace, whichever is the weaker, to resist rupture from internal pressure or collapse of the furnace from pressure.
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23-What additional method is used in calculating the maximum allowable pressure of a Manning boiler?
It is necessary to figure the strength of the shell at its point of greatest diameter, between the reverse flange and the top row of stay bolts.
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