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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24-Is the economic boiler internally fired?
No, Its combustion chamber is steel-encased, but the casing is not a pressure part of the boiler.
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25-Name four internally fired boilers?
Vertical tubular, locomotive, scotch marine, and scotch dry-back.
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26-When breaking a gasketed joint on a power boiler, should the gaskets be reused?
Handhole and manhole gaskets should not be reused but replaced by new gaskets to prevent leakage when the boiler is returned to service.
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27-What precaution should be taken before closing drum manholes and setting doors on a steam generator?
Make sure all tools, rags and similar foreign objects are removed and that all personnel that worked in the steam generator have exited from the unit.
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28-A code boiler is installed in a plant. Why is it necessary for a jurisdictional or authorized inspector to make an inspection again before the boiler is placed in operation?
A code boiler inspection during construction by an authorized inspector, however the installation must also be inspected for jurisdictional requirements on boiler supports, piping safety relief valves, blowdown, stop and feed valves and connections, instrumentation and controls, and combustion safeguards that must meet jurisdictional installation requirements.
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29-How are stays and stay bolts checked for soundness during inspections?
All stays should be checked to see if they are still in even tensions, the welded or riveted connections should be checked for signs of cracks, weld washout or similar signs of excessive wear and tear. Stay bolts are usually “sounded” by tapping the end of the bolt to note if the ring or sound is the same on all stay bolts. A cracked or broken stay bolt will give a different sound.
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30-How is circulation obstruction checked on a firetube boiler?
To check for scale and deposits beyond the top of the tubes, a small light can be lowered between the tubes to observe if scale and deposits are plugging the space between the tubes or in water legs.
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31-Why should a boiler operator be familiar with manual operations on a b oiler equipped with automatic combustion controls?
Manual operations should be periodically practiced in the event that emergency conditions develop with the automatic controls.
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32-Should fuel solenoid valves on automatic boilers be of the manual reset type?
On power boilers, it is important to determine why the fuel solenoid valve shut the fuel off. For example, it could be because of poor combustion at a the burner activating the flame safeguard system. Therefore, the fuel solenoid valve should be the manual reset type to prevent a dangerous condition developing. As operator can first check out why the fuel was shut off.
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33-Two high pressure boilers are connected to a common steam pipe header. What are the code requirements on the connections to the header from each boiler?
The code and ASNI B31.1(power piping) require boilers connected to a common steam pipe header to be fitted with two stop valves having free-blow down drain between them to check on the tightness of valve closure. The first stop valve near the boiler must be an automatic non return valve to prevent back flow. The second valve should be of the outside screw and yoke(OS&Y) type, and if steam outlet is over 2 in. it must be of the rising spindle type.
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34-Explain the difference between a bag and blister if found on the shell of a firetube boiler?
A bag is a deformation or bulge caused by local overheating of the shell and extends through the thickness of the shell.
-A blister is a partial separation on the shell that doesn not extend through the thickness, but is of a scablike nature, usually caused by impurities getting into the metal during the steel rolling operation.
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35-Why are manholes and handholes usually found oval in shape?
IT facilitates removing the covers from the boiler during maintenance or inspection periods. Oval manholes provide extra length for climbing into the boiler without making the opening so large that extra material would have to be removed , requiring more reinforcement around the opening. The long axis of manholes is always placed girthwise on the shell.
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36-When inspecting an old HRT boiler, it is found that the boiler has three stays on one side of the top manhole and four stays on the other side. Must the pressure be reduced?
This condition should be called to the attention of a jurisdictional inspector. He will determine the permissible pressure by checking the loading and pitch between stays that are necessary to carry the present boiler allowable pressure. If three stays satisfy code requirements on load carrying and permissible pitch, nothing further may need to be done. If four stays are required on each side, then an additional stay will have to be installed or pressure reduced. Page chapter 2
37-A solid stay bolt under 8 in. requires what size telltale hole, and for what distance?
Per code, the hole must be at least 3/16-in. diameter and must extend ½ inch. Beyond the inside surface of plate being stayed.
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38-What effect does the length of a furnace have on its strength?
Length increases the bending moment the furnace must resist against collapsing. This is the reason for stiffening the furnace by installing for example, an Adamson ring along its length.
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39-What is the maximum distorting permissible by the code in the diameter of a welded boiler shell or drum.?
1 percent of mean diameter.
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40-It is permissible to locate a tube hole in a welded joint?
Per code rules , it is permissible however, the weld after the hole is made must be checked for cracks and tears by the magnetic particle inspection to make sure it was not affected.
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41-Under what conditions may stay bolts be welded per code rules?
The joint must be prepared per code rules for welding, an d the welding procedure and welder must meet code qualifications.
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42-What minimum thickness must a firetube shell and tube sheet be on a 60-in-ID diameter boiler?
Per code, 3/8 in. for shell and ½ in for tube sheet.
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43-On what type of boiler would you find an Adamson furnace, and per code, what is the minimum section length and thickness of an Adamson furnace?
SM boiler, 18-in. length, 5/16 in. thick per section 1, PFT part. Page 61 chapter 2
44-A wet bottom boiler is to be installed in the boiler house. What minimum distance is required between the bottom of the shell and the floor?
A distance of 12 in. is required so that the bottom of the shell is accessible for inspection or repair.
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45-A gauge glass on a horizontal firetube boiler shows the lowest possible water level in the glass. How many inches above the tubes should this level be in a code boiler?
The code requires water to be 3 in. above the tubes when the water in the glass is at its lowest level. chapter 2
46-The code does not permit welds in shells of a firetube boiler to be in contact with primary furnaces gases. Define primary furnace gases.
Primary furnace gases are those that are in the fire side zone area where the temperature exceed 850 degrees F. Page 75-76 chapter 2
47-For a firetube boiler, per code, what is the minimum size of washout plugs and access doors into setting?
Washout plugs must be at least 11/2 in., and access doors must have a minimum area presented by a 12- by 16- in. rectangle with 11 in. being the least permissible dimension.
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48-Why are steam domes used in locomotive boilers?
To provide the drier steam and also to provide additional steam storage space for use during steep train climbs.
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49-(a)Why do the upper ends of tubes in VT boilers which are not covered with water not burn out?
Because the products of combustion at this point are at such a temperature that cooling of the tube ends is provided by the steam and prevents the upper ends of the tubes from burning. Page 68 chapter 2
(b) Why do the rear ends of tubes on a high temperature boiler leak in case of low water?
The products of combustion at the front tube sheet are at a lower temperature than at the rear tube sheet, so that when low water occurs, the tubes overheat and expand; at the same time the rear tube sheet overheats and the tube hole expands and gets larger, so that the seating of the tube produced by the expander is destroyed, and therefore, leaking occurs at the rear ends. Page 68 chapter 2
50-Which type of boiler, fire tube or water tube, has the most heating surface in the tubes?
The code states heating surface shall be computed for that side of a boiler surface exposed to products of combustion. Therefore, a water tube contains more heating surface than a fire tube of the same diameter.chapter 2
51-When is a manhole required in the front tube sheet below the tubes in a HRT boiler?
When the boiler is 48-in. diameter or larger.Page 50 chapter 2
52-When is a manhole required above the tubes of a horizontal firetube boiler?
If externally fired, for boilers of 40-in. diameter or over, if internal fired, for boilers of 48-in. diameter or over.
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53-What is the minimum face width of a manhole flange for a gasket bearing surface?
11/16-in. Page 51 chapter 2
What could be done if the flange were only 7/16 in thick?
A steel ring could be shrunk on the flange, and the double face could be machined for a bearing surface. chapter 2
54-Name 4 ways of supporting a circular furnace subjected to external pressure?
It may be self supporting, stay-bolted- corrugated, or equipped with Adamson rings. chapter 2
55- What was the maximum permitted length of a course in an HRT boiler of riveted construction?
12 feet page 56 chapter 2
56-what are advantages of submerged top tube sheets in a VT boiler?
A submerged top tube sheet of a VT boiler protects the upper tube sheet and tube ends from overheating and possible fire cracks.
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57-What size limitations must not be exceeded for a firetube boiler to be classified as a miniature boiler?
The following cannot exceed: Inside diameter, 16 in. Gross volume, 5 ft3, Water heating surface 20ft2 Allowable working pressure 100psi Page 15 chapter 1
58-Name three advantages in using a corrugated furnace in a scotch marine boiler.
The corrugated SM type of furnace offers the following advantages over a plain furnace:
The corrugations stiffen the furnace si it does not collapse as easily from jexternal pressure as does a similar thick, plain furnace
The corrugated furnace permits more expansion and contraction to take place as a result of the bellows like action of the corrugations
There is a slight increase in the heat absorbing area over a plain furnace of the same diameter and length.Page 61 chapter 2
59-How can the water level in a steam boiler be checked if the water gauge glass is temporarily out of service?
By using the water gauge test cocks that are located on the water column.Page 56 chapter 2
60-What space consideration is required when installing horizontal firetube boilers?
Sufficient room must be left in the front or back of the boiler so that tubes can be replaced. Page 54 chapter 2
61-Why did the code require HRT boilers over 72 –in. diameter to be supported by outside suspension type of settings?
Brickwork settings use don smaller HRT boilers could not support the heavier load that a larger boiler full of water would impose on the setting, and crushing or crumbling of the support could result.
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62-What is a strong back?
It is a bar bolted to the tube sheet to prevent the sheet from buckling when the stays are put in tension before the tubes are installed.
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63-In checking an HRT boiler, what is the difference between a through brace and a through to head brace? Where is each used?
Why?
The through brace has washers and nuts on each end. The throught to head brace has nuts and washers on one end, the other end is forged into tan eye that is held clear of the rear head by a pin or other construction.
The through strays may be used above the tubes, for the rear outside nuts are protected from burning off by the rear arch.
The through to head braces are used below the tubes where the rear ends have to be protected from the high temperature gases.
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64-A locomotive boiler is to be exhibited at a state fair and requires approval for operation.
What are the sheets of a locomotive boiler?
Barrel or shell, smokebox tube sheet, dome shell, dome head, wrap per sheet, throat sheet, firebox side sheets, firebox tube sheets, crown sheet, inside door sheet and outside door sheets.
Where is the most dangerous part of the boiler in case of low water?
The crown sheet.
From which end are tubes removed and replaced?
The smokebox end.
How are the firebox sheets supported?
The side, door and throat sheets are supported by stray bolts. The crown sheet is supported by radial or girder stays.
Where is the usual location for the manhole?
In the dome head, or in the shell if no dome is used.
How many manholes are used in a locomotive boiler?
One. The part of the barrel over the tubes is the only part of the interior that is accessible.
What should be the lowest level for the bottom nut of the gauge glass?
The lowest visible part of the glass should be at lease 3 in. above the highest part of the crown sheet. Page 58 chapter 2
65-For what size firetube boiler does ASME CSD-1 and addenda’s titled, “controls and safety devices for automatically fired boilers” apply?
This is also an ANSI standard and may be require by jurisdictional adoption as an installation requirement for automatically fired boilers whit inputs of 400,000 to 12,500,000 Btu/hr. page 22 chapter 2
The firetube boiler is the most prevalent boiler used for heating and commercial and industrial process applications.
yes
Law of science that a fluid exerts itself in an equal amount in every direction.
yes
Types and arrangements
HRT horizontal return tubular
Economic or firebox type Locomotive fire box type Scotch marine type Vertical tubular Vertical tubeless
Fire tube holes are finished 1/16 in. larger in diameter than the outside diameter of the boiler tube so as to permit a tube with scale to be drawn from the tube sheet without damage to the tube sheet hole.
`
Page 47 for the fire tube shell and drum thickness per code.
yes
Manhole and hand holes page 50
A manhole is required in the upper part of the shell or head of firetube boilers over 40 in in diameter.
A hand hole above the tubes will suffice for very small boilers.
Water level
Horizontal fire tube type boilers must be set so that the lowest reading in the water glass is at least 3 in. above the highest point of the tubes.
Heating surfaces.
On all boilers heating surfaces are measured on the side receiving heat.
For firetub boilers this includes projected tube area(diameter times length) and any extended surface of the boexes, tube sheets, and the projected areas of headers exposed to the products of combustion.
Exception for vertical firetube steam boilers, require only tube surfces up the middle of the gauge class be used.
Heat release rates. Page 51
2 rates used
see blow.
1-Volumetric
is the heat release rate ratio of
Maximum fuel imput at boiler rating x fuels high heat value/ft3 of furnace volume
Oil fired 35MBtuh/ft3; maximum 45 MBtuh/fts
Gas fired 40MBtuh/ft3; maximum of 50 MBtuh/ft3
2-Effective Projected Radiant Surface
Fuel release rate/ft2 of furnace radiant surface.
Oil fired 180,000 Btuh/ft2
Gas fired 200,000 Btuh/ft2
