Chapter 1Boiler Systems, Classifications, and Fundamental Operating Practices

Question 1

How would you define a boiler?

Answer 1

A boiler is a closed pressure vessel in which a fluid is heated for use external to itself by the direct application of heat resulting from the combustion of fuel (solid, liquid, or gaseous) or by the use of electricity or nuclear energy.

Question 2

What is a steam boiler?

Answer 2

A steam boiler is a closed vessel in which steam or other vapor is generated for use external to itself by the direct application of heat resulting from the combustion of fuel (solid, liquid, or gaseous) or by the use of electricity or nuclear energy.

Question 3

What is a high pressure steam boiler?

Answer 3

A high-pressure steam boiler generates steam vapor at a pressure of more than 15 psig. Below this pressure, it is classified as a low pressure steam boiler.

Question 4

4-Define a miniature high pressure boiler.

Answer 4

According to section 1 of the ASME boiler and pressure vessel code, a miniature boiler is a high pressure boiler which does not exceed the following limits: 16 in. inside diameter of shell, 5-ft3 gross volume exclusive of casing and insulation, and 100-psig pressure. If it exceeds any of these limits it is a power boiler. Found on page 15

Question 5

5-What is a power boiler?

Answer 5

A power boiler is a steam or vapor boiler operating above 15 psig and exceeding the miniature boiler size. This also includes hot-water heating or hot-water supply boilers operating above 160psi or 250 degrees Fahrenheit. Found on page 15

Question 6

6-Define a hot water heating boiler?

Answer 6

A hot water heating boiler is a boiler used for space hot water heating, with the water returned to the boiler. It is further classified as a low-pressure if it does not exceed 160 psi or 250 degrees Fahrenheit. But if it exceeds it becomes a high pressure power boiler. Found on page 15

Question 7

7-What is a hot water supply boiler?

Answer 7

A hot water supply boiler furnishes hot water to be used externally to itself for washing cleaning ect. If it exceeds 160psi or 250 degrees it becomes a high pressure power boiler.
Found on page 15

Question 8

8-What is meant by boiler horsepower?

Answer 8

A boiler horsepower is defined as the evaporation into dry saturated steam of 34.5lb/hr of water at a temperature of 212 degrees. Thus one boiler hp by this method is equivalent to an output of 33,475 btu/hr. In the past it was commonly taken as 10ft2 of boiler heating surface. Found on page 15

Question 9

9-The symbol NB is often noted on boilers, with a number following it. What does this stand for?

Answer 9

NB stands for National Board of boilers and pressure vessel inspectors. It means that the boiler’s design and fabrication were followed in the shop by an NB commissioned inspector, including the witnessing of the hydrostatic test and signing of data sheets required by ASME. Found on page 30

Question 10

10- What is meant by heating surface in a boiler?

Answer 10

This is the (fireside) area in a boiler exposed to the products of combustion. This area is usually calculated on the basis of areas on the following boiler element surfaces: tubes, fireboxes, shells, tube sheets, and projected area of headers. Found on page 17

Question 11

11- Define the terms IBR rate, SBI rated and EDR

Answer 11

IBR stands for the institute of boiler and radiator manufacturers, which rates the output of cast iron boilers in net and gross output in Btu per hour. Gross output is further defines as the net output plus an allowance for starting, or pickup load, and a piping heat loss.
SBI stands for the steel boiler institute. The SBI boiler out put rating tends to s how the sum of SBI net ratings in BTU per hour or pounds per hour, plus 20 percent extra for piping loss, not including the pickup allowances note under IBR ratings. The SBI requires the number of square feet of heating surface to be stamped on the boiler.
EDR stands for equivalent direct radiation. It specifically refers to equivalent square feet of steam radiation surface. It is further defined as a surface which emits 240 BTU/hr with a steam temperature of 215 degrees at a room temperature of 70 degrees. With hot water heating, the value of 150 Btu/hr is used with a 20 degree drop between inlet and outlet water. This term is used by architects and heating engineers in determining the area of heat transfer equipment require for a space. Found on page 18

Question 12

12-Name three terms used to indicate boiler output.

Answer 12

1-For steam boilers, the actual evaporation is in pounds per hour. For hot water boilers, the BTU per hour outputs for the given pressures and temperatures are stamped on the boiler. Today this is the preferred method.
2-Square feet of heating surface.
3-Boiler horsepower. Found on page 17

Question 13

13- What is a supercritical once through boiler?

Answer 13

This is a boiler which operates above the supercritical pressure of 3206.2 psia and 705.4 degrees saturation temperature and which has no fluid recirculation when operating at full pressure and temperature. The fluid is brought up to pressure and temperature in series connected fluid passes; thus the term once through is applied. Found on page 16

Question 14

14- Above what temperature and pressure does a hot water boiler system become a high temperature hot water boiler system?

Answer 14

A hot water boiler becomes a high temperature hot water (HTHW) system when the water temperature exceeds 250 degrees and the pressure is over 160psi
Found on page 15

Question 15

15- What is the main reason for using thermal fluids such as dowtherm and glycol in process requiring heat?

Answer 15

The thermal fluids are used to get thigh temperatures at low pressures which may be difficult to obtain with ordinary steam boiler equipment.
Note: that a pressure of 3206.2 psia is needed to obtain a saturation steam temperature of 705.4. This temperature can be obtained with some thermal fluids at a pressure below 50 psi. found on page

Question 16

16-Name three pressure limiting devices needed on a steam heating boiler per ASME code requirements.

Answer 16

1- An operating pressure cut off switch that automatically cuts off the fuel supply when the desired pressure is reached.
2-An upper limit pressure control switch, set no greater than 15 psi that automatically cuts off the fuel supply when the upper pressure is reached.
3-At least one spring loaded pop type safety valve, set and sealed to discharge at a pressure not greater than the maximum allowable working pressure of the boiler and with a capacity sufficient that the pressure of the boiler cannot rise 5 psi above the stamped maximum allowable pressure on the boiler. Found on page 22

Question 17

17-What is the purpose of the water level control on a steam boiler?

Answer 17

To maintain the proper water level in the boiler by the control starting the boiler feed pump when there is a demand for water by the lower limit level switch, and by shutting the pump off when the proper water level is reached. (upper limit). Found on page 22

Question 18

17-What is the purpose of the water level control on a steam boiler?

Answer 18

To maintain the proper water level in the boiler by the control starting the boiler feed pump when there is a demand for water by the lower limit level switch, and by shutting the pump off when the proper water level is reached. (upper limit). Found on page 22

Question 19

19-What is the purpose of the low water fuel cutoff?

Answer 19

To shut the fuel off to the burner before the water in the boiler drops below the safe permissible level and thus prevent overheating damage to the boiler. Found on page 25

Question 20

20-If the water drops below the bottom of the sight glass, and the burner does not shut off, what steps should be taken?

Answer 20

Shut the fuel valve to the burner, and shut off the electricity to the boiler, assuming this is a small automatic type steam boiler. Let the boiler cool off, and then check the controls in order to determine why the level controller and the low water fuel cutoff did not function as designed.

Question 21

21-How often should the low water fuel cutoff be tested on automatic boilers?

Answer 21

At least once per day and each shift if more than one shift of operation is in effect.
Found on page

Question 22

22-Why should the water column and low water fuel cutoff chamber be flushed daily by draining the respective devices?

Answer 22

Both conditions could cause a lack of air to flow into the boiler room, and this will result in possible incomplete combustion to occur in the boiler. This can create air-fuel ratio problems with the burner control and also create a possible health hazard with the formation of carbon monoxide from incomplete combustion.

Question 23

23-Why should air openings to a boiler room be kept clean and clear of any obstructions that could hinder airflow into the room?

Answer 23

Both conditions could cause a lack of air to flow into the boiler room, and this will result in possible incomplete combustion to occur in the boiler. This can create air-fuel ratio problems with the burner control and also create a possible health hazard with the formation of carbon monoxide from incomplete combustion.

Question 24

24- What is the output in pounds per hour and Btu per hour of a boiler rated 750hp?

Answer 24

Output= 750(34.5)=25,875 lb/hr

Output=750(33,475)=25,116,250Btu/hr found on page 18

Question 25

25-Calculaste boiler efficiency, using the steam generated versus the fuel consumed. You are given that for one calendar month of regular operation, the coal consumed is 682,000 lb and the steam generated is 6.4 million lb at 179 psig and superheated to a total temperature of 520 degree f. Assume that the heat content of coal as fired is 13,260 Btu/hr, and that the feed water temperature is 208 degrees f.

Answer 25

First the actual evaporation per pound of coal fired is
6,400,000/682,000= 9.40 lb steam/lb coal
The absolute steam pressure is
179+15= 194 lbs abs
Then, the steam tables show that the total heat of 1 lb of steam at 197-lb absolute pressure and 520 degrees f is 1280.4 Btu. With the feed water temperature at 208 degrees f, its heat content above water at 32 degrees f is merely 208-32=176 Btu. Thus the heat put into each pound of steam produced by the boiler is 1280.4-176.0=1104.4 Btu. The heat put into 9.4 lb of steam will be 10,381 Btu. Then, boiler efficiency equals heat put into 9.4-lb steam divided by the heat in 1 lb of coal, or
10,381/13,260x100%=78.3 efficiency found on page 12/13

Question 26

26-(a) feed water at 300 degrees f is converted into superheated steam at 800 psig and 900 degrees f. How many Btus are needed to do this?

Answer 26

(b) If this was a boiler burning coal with 13,600 Btu/hr heat value and with evaporation being 9.4 lb of water per pound of coal, determine boiler efficiency using output-input method.

a-From the superheat steam table(table 3 in Fig. 1.5) enthalpy at 800 psig and 900 degree f is 1455.4 Btu/lb. From table 1, saturated liquid at 300 degrees f has 269.6 Btu/enthalpy. Heat needed to convert the liquid into superheated steam is 1455.4-236.6=1185.8 Btu/lb.
b-Output is thus 1185.8 x 9.4= 11,140Btus. Input is given as 13,600 Btus. Efficiency is 11,140/13,600 =0.820 or 82% found on page 12

Question 27

27-Why should a boiler not be drained while the fireside is hot?

Answer 27

This is necessary to avoid baking sludge on the tubes and other heating surfaces, and also to avoid high thermal stresses developing from too rapid cooling. This will prevent leakages at gasketed joints and tube rolls and similar seams affected by expansion and contraction. Found on page

Question 28

28-What is a compound gauge?

Answer 28

A compound gauge is a pressure gauge that shows pressure on one half of its dial, while the other half shows vacuum. It is used where the heating system may vary from a pressure to vacuum condition. Found on page

Question 29

29- What are the advantages in converting boiler controls and instrumentation to digital based technology?

Answer 29

Digital based instrumentation and controls permit finer tuning of input and output on a boiler system. Closer control of thermal efficiency is achieved by approaching set points to designed operating limits. Improved emission is also achieved by more precise control of the combustion process, such as air fuel ratios, and also of any downstream cleanup process equipment, if so installed, as in coal burning plants. Fewer personnel are required to operate the plant, because a central control room provides video display of operating conditions for each loop of the boiler system. Appropriate warnings, alarms, and trips can be incorporated into the control system, usually employing appropriate computer technology. Found on page

Question 30

30-How are diagnostic capabilities incorporated in modern boiler controls?

Answer 30

One manufacture of moderate capacity boilers provides many diagnostic displays, such as: Boiler functions of input and output displayed on video screens, with the operator controlling any variable from set points by touch screen buttons or key pad interface; start up or other operating problems displayed on the video screen with explanation as to cause. Typical situations displayed: water level to low; fan not operating, gas pressure too low; air curves to show the air required for the fuel being burned. The diagnostic display on the cause of a problem permits the operator to correct the problem at once instead of initiating a search for cause. Found on page

Question 31

31-Differentiate between ISO 9000,9001,9002,9003,9004

Answer 31

The combined standards are designed to establish a quality control management system. ISO 9000 and 9004 define the terms and provide the system elements required to meet the applicable standard, while 9001,9002 and 9003 present the various activity system models. ISO 9001 specifies quality assurance in design, production, installation, and servicing of a designated product. ISO 9002 applies only to production and installation. ISO 9003 applies to final inspection and testing. See table 1.1 for more details on the ISO 9000 series of standards.
Found on page 35

Question 32

32-Briefly describe the ASME code requirements in section 1 (power Boilers) for a quality control program for fabricating a code boiler.

Answer 32

1-management support by naming a quality control manager to implement the program.
2-An organization chart showing where quality control is to be applied in design, material selection, inspection, record documentation, and the check off sheets to be applied at each step of the manufacturing cycle.
3-Provisions for correcting defects per code rules.
4-periodic checking of gauges, NDT equipment, and similar instruments.
5-Maintaining forms and data of recorded quality control performed for future reference.
6-Maintaining records of welder and welding procedure qualification tests as well as records of NDT and heat treatment performed. Found on page

Question 33

33- What stamp is required on a field assembled power boiler when it is assembled by a contractor and not the boiler manufacturer?

Answer 33

He contractor must be qualified by the ASME to stamp the assembled boiler with an “A” stamp.

Question 34

34-Why are flat surfaces above a certain area stayed or braced for a boiler?

Answer 34

Pressure acting on flat surfaces that are not thick enough will bulge the plate into a spherical shape and possibly cause a rupture. The braces or stays strengthen the flat surfaces in order to avoid this.

Question 35

35-Why should steam leaks in a boiler system be repaired as soon as possible?

Answer 35

All leaks should be immediately repaired to avoid further damage and also to prevent personal injury. Loss of steam from leaks is also energy wasted, which increases fuel costs to the plant.

Question 36

36- What hazard can be created by opening a steam valve quickly?

Answer 36

The sudden change in pressure and temperature on connected piping may cause a water hammer, vibration, and even pipe rupture at abrupt pipe run changes, such as elbows.

Question 37

37-What are recognized authorized inspection agencies per the
ASME boiler code.?

Answer 37

The code designates AIA as those inspection organizations employing inspectors qualified by written examination under the rules of jurisdiction, consisting of a state or municipality of the unites states or Canadian province that has adopted one or more sections of the boiler code, or of an insurance company authorized to write boiler and pressure vessel insurance in the jurisdictions.

Question 38

38-What additional training must an NB commissioned inspector obtain to merit the “A” endorsement to make manufacturer’s shop inspection per NB rules?

Answer 38

The A endorsement requires successful completion of 30 hours of formal training beyond the NB commission and an additional 80 hours of supervised on the job training in a manufacturer’s shop.

Question 39

39-What experience requirements must an individual employed regularly by an AIA have before being permitted to take the 2 day examination for an NB certificate to competency as an NB commissioned inspector of boilers and pressure vessels?

Answer 39

The present requirements are practical experience in design, construction, maintenance, operation or inspection of high pressure boilers and pressure vessels that must consist of the following:
1-ME degree plus 1 year of practical experience
2-other engineering degree plus 2 years of practical experience
3-at least a high school education plus 3 years of practical experience.
The candidate must also study the following ASME code sections: Section 1 – power boiler; section IV – heating boilers; section IX – welding qualifications; section V-nondestructive examination, and the national board inspection code.

Question 40

40-What power boiler is classified as a miniature boiler?

Answer 40

A high pressure boiler that does not exceed any of the following: inside diameter of shell, 16 in; 20ft2 of heating surface; 5 ft3 gross pressure part volume; 100 psig working or allowable pressure.

Question 41

41-Is gauge or absolute pressure used in the ASME boiler code for maximum allowable pressure for a boiler?

Answer 41

The ASME boiler code refers to gauge pressure, or the pressure above atmospheric pressure in psi, because this is what is read by operating people or users of boilers.

Question 42

42-How does a section of ASME boiler code become a legal requirement in a jurisdiction?

Answer 42

Usually a legislative body of a jurisdiction established the mandatory applicability of the code rules on a section basis, such as sections I,IV VIII, or even parts thereof, and then this becomes a legal requi8rement for a location within that jurisdiction. Jurisdictional enforcement machinery and additions or deletions to the ASME code may be adopted by the jurisdiction, such as state certificate of operation fees, and state inspection fees, which are not covered by the ASME code.

Question 43

Fundamental operational responsibilities

Answer 43

Water levels, low water, low water cutoff, gauge cocks, safety valves, burners, boiler internals, the outside of the boiler, leaks, when taking a boiler out of service, dampers, idle boilers, purging, preparing a boiler for inspection, maintain boiler water treatment testing, maintain proper blow down.

Question 44

Flow of heat in a boiler 3 types

Answer 44

1-Conduction-the transfer of heat from one part of a material to another or to a material with which it is in contact .
Btu per hour per square foot per degree Fahrenheit per foot.
Q=kAT/L
k=coefficient of thermal conductivity
2-Convection- Is the transfer of heat to or from a fluid(liquid or gas) flowing over the surface of a body. It is further refined into free or forced convection.
Free convection is natural convection causing circulation of the transfer fluid due to a difference in density resulting from temperature changes.
Forced Convection results when circulation of the fluid is made positive by some mechanical means, such as a pump for water or a fan for hot gases.

3-Radiation- is a continuous form of interchange of energy by means of electromagnetic waves without a change in the temperature of the medium between the two bodies involved.

Boilers utilize all 3 means of heat transfer.

Question 45

Enthalpy means the heat content of the fluid.

Answer 45

Enthalpy of saturated liquid which is the heat contents of the water at a certain pressure an temperature under consideration.
Enthalpy of evaporation which is the heat required to evaporate 1 lb of water to steam at that pressure and temperature.
Enthalpy of saturated vapor which is the heat content of the saturated steam at the pressure and temperature being considered.

Question 46

Sat Liquid

Answer 46

Sat Liquid means liquid water at the saturation or boiling temperature .

Question 47

Boiler Types

Answer 47

Boiler, high pressure steam boiler, a miniature high pressure boiler, a power boiler, a low pressure boiler, a hot water heating boiler, a hot water supply boiler, a waste heat boiler, a supercritical boiler.

Question 48

Type of construction

Answer 48

Cast iron boiler, 
3 types    
1-vertical section
2-Horizontal section
3-Samall cast iron boilers

Question 49

Steel boilers can be of high pressure or low pressure type and today are usually welded const.
2 classes

Answer 49

1-Firetube boilers- the products of combustion pass through the inside of tubes with the water surrounding the tubes.
2-Watertube boilers- the water passes through the tubes and the products of combustion pass around the tubes.

Question 50

A boiler horsepower is defined as.

Answer 50

A boiler horsepower is defined as the evaporation into dry saturated steam of 34.5 lb/hr of water at a temperature of 212 degrees F.
Thus 1 boiler hp by this method is equivalent to an output of 33,475Btu/hr, and was commonly taken as 10square feet(ft2) of boiler heating surface.

Question 51

The term heating surface

Answer 51

The term heating surface is also used to define or relate to the output of a boiler. The heating surface of a boiler is the area, expressed in square feet, that is exposed to the products of combustion.

Question 52

A comparison of output ratings based on horsepower, heating surface, and pounds per hour can be made by assuming a boiler has a nominal horsepower rating of 500hp.

Answer 52

1-The heating surface rating would be 5000ft2under the old rule of 10ft2/hp
2-The steam output in pounds per hour would be 500 x 34.5= 17,250 lb/hr
3-for a hot water heating boiler, the output would be 500 x 33,475= 16,737,500 Btu/hr.

Question 53

In heat load calculations the terms IBR-rated, SBI-rated and EDR.

Answer 53

IBR institute of boiler and radiator manufacturers
SBI Steel boiler institute
EDR stands for equivalent direct radiation

Question 54

Hot water systems

Answer 54

Hot water supply systems for washing
Space heating systems of the low pressure type, building heating systems
High temperature high pressure water system. Supertherm systems. Operates at temp above 250 degrees and pressures over 160psi

Question 55

Both the hot water heating system and the high temperature hot water system requires.

Answer 55

Both the hot water heating system and the high temperature hot water system requires some form of expansion tank in order to permit the waster to expand as heat is applied. Sometimes a common problem occurs that the expansion tanks lose their air cushion, so that the water can no longer expand.

Question 56

Protective devices for hot water systems

Answer 56

A pressure or altitude gauge
A thermometer gauge
Two temperature controls   operating limit control and upper limit control
A low water fuel cutoff
All electric control circuitry
Spring loaded pressure relief valve
Flame safeguard safety controls