- What is a water tube boiler? What are five advantages and five disadvantages of a water tube boiler? Name four types of water tube boilers. SPO 6-7-8 LPB 2-3 BOW 2-3-4
In a water tube boiler, products of combustion pass around the tubes containing boiler water.
Advantages:
a. Rapid steamers
b. Use less water
c. Less chance of explosion
d. No flat surfaces
e. Smaller tube style
Disadvantages:
a. Elaborate settings
b. Field assembles
c. Initial cost per pound of steam is higher
d. Greater number of openings thus more air infiltration
e. Requires more floor space
4 types:
B&W, Stirling, Heine, Riley Consolidated, F.M. Package, MH, Cross drum, Straight tube
- What is a fire tube boiler? What are five advantages and five disadvantages of a fire tube boiler? Name four types of fire tube boilers. SPO 6-7-8 LPB 2-3 BOW2-3-4
Products of combustion pass through tubes or flues surrounded by water.
Advantages:
a. Low initial cost
b. Compact very little setting required
c. Factory assembled for fast installation
d. Can be made portable
Disadvantages:
a. Liable to disastrous explosions because drums and joints are set over the fire
b. Inaccessible for inspection
c. Poor circulation
d. Slow steamers
e. Inefficient
f. Pressure & capacity are limited
4 types:
H.R.T., Locomotive, Scotch Marine, Vertical Fire tube
- What type stays are used in wet back (Scotch Marine) type boilers? SPO 6 BOW 2-34
Stay bolts & through stays. These will sometimes have a telltale drilled through them.
- Describe a sectional boiler. LPB 2 BOW 2-3-4
The sectional headers are built up of vertical sections or units. A sufficient number of sections are clamped together to form the desired size boiler. These boilers can be erected in an existing building by carrying them in piece by piece
- What is a superheater? What are the advantages of a superheater? SPO 6-7-8 BOW 2-3-4
A device used to raise the temperature of steam without raising its pressure.
Advantages:
a. Increased efficiency of the boiler
b. Delivering Dryer steam
c. Dryer steam can be transmitted long distances with minimal heat loss
d. With drier steam, condensation and erosion are reduced
- What is a radiant type superheater? What is a convection type superheater? What is the third type of superheater? SPO 6-7-8 BOW 2-3-
Radiant type superheater is placed in position to absorb radiant heat from the furnace by direct radiation. It is set over the fire.
Convection type is placed in the gas passage of the furnace usually between the first and second pass. Little to no radiation will reach this type.
3rd type is a combination of radiant & convection
- What is an economizer? What is an air pre-heater? SPO 6-7-8 BOW 2-3-4
Economizer is a heat exchanger located in the breeching between the boiler & stack. It is designed to recover waste heat from the products of combustion by pre-heating the feed water. (Greater economy in heating feedwater)
Air pre-heater consists of a series of tubes or plates that have hot gases on one side and incoming air on the other. Heat in the hot gases leaving the boiler is recovered by the incoming air.
(Both of these reduce stack temperatures & increase the boiler efficiency)
- What is a waterwall? SPO 5-6-7 BOW 2-3-4
Set of tubes containing boiler water set in the refractory. They absorb heat that would otherwise be lost to the refractory & they increase the capacity of the boiler
- What is A.S.M.E. and its purpose? What code information is stamped on the boiler? What is an A.S.M.E stamp? Where are the code markings found on a boiler?
SPO 6-7-8 LPB 2-3 BOW 2-3-4
American Society of Mechanical Engineers has written a set of minimum standards for the safe construction of pressure vessels.
Stamped on the boiler shell or a plate attached to the shell will be the model & serial numbers, safe working pressure, date of manufacture, name of manufacturer, type of material used, horsepower rating, square feet of heating surface, steam generation in PPH, fuel designed for the ASME stamp. ASME symbol stamp will identify the boiler or accessory type. On a fire tube boiler it may be located on the right side near the front by the water column. On a water tube boiler it will be located next to the manhole on the steam drum.
- What is the cross section of a 1” bolt? SPO 6-7-8 BOW 2-3-4
D xD x.7854 (¼ π)
1 x 1 x .7854 = 0.7854 sq. in.
(Show your work & label everything)
- What is an alloy? Name five. SPO 6-7-8 BOW 2-3-4
A mixture of two or more metals
Brass, Steel, Stainless Steel, Pewter, Cast Iron, Bronze, Babbitt, Molybdenum, Monel, Bell metal
- At what pressure is the use of cast iron fittings permitted? SPO 6-7
15 PSI or 250 degrees, not to exceed either one
- What is meant by factor of safety? SPO 6-7-8
The comparison of the tensile strength to the actual working stress.
The bursting pressure divided by the working pressure.
- What is the factor of safety for boilers, flywheels and pipe? SPO 6-7-8
New Boiler is 4
Preowned Boiler constructed to ASME code is 5
Flywheel is 3
Pipe is 8
- What is a lap joint? What is a butt joint? What is a butt strap joint? SPO 6 BOW 2-3-4
Lap joint is when one plate overlaps the other & is joined
Butt joint is when two ends of the plate meet end to end and are joined.
Butt Strap joint is when two ends of the plate meet end to end and are joined by a plate. One Plate is a single butt strap joint. Two plates is a double butt strap joint.
- Is the longitudinal joint the strongest part of the boiler? SPO 6-7-8 BOW 2-3-4
NO. It is the strongest type joint but any joint is the weakest part of the boiler.
- Two boilers are made of the same grade of steel, same thickness of plate and same type of joints. One is 30” diameter the other is 60” diameter. Which will withstand the greatest working pressure and demonstrate your answer. SPO 6-7-8 BOW 3-4
The 30” boiler has less pressure on the shell
30 x 30 x .7854 x 120 PSI = 84.823 lbs total pressure.
60 x 60 x .7854 x 120 PSI = 339.292 lbs total pressure.
(Show your work & label everything)
- What are tube ligaments? SPO 6-7-8 BOW 3-4
Area between the tube holes on the tube sheets. (lands)
- What type stays are used in the heads of water tube boilers and why? SPO 6-7-8 BOW 2-3-4
There are NO stays. Head of the boiler drum is shaped with a die that dishes and forms them into the shape they would take as a result of the pressure to which they would be subjected
- Why is a row of tubes sometimes left out of an H.R.T. boiler? SPO 6-7-8 BOW 2-3-4
To improve circulation which reduces carryover
