Designing to Boiler Codes

All the leading boiler-making countries have their own boiler and pressure vessel codes. These codes evolved after the early boilers experienced disastrous explosions on account of failure of PPs due to the rise of internal pressure. The boiler codes are essentially extensions of pressure vessel codes customized for fired equipment. It should be clear that the boiler codes are concerned with safety aspects only and not with the sizing or thermal design of boilers. Besides the boilermakers and steam users, the insurance companies, the labor and safety departments of the government, and the bureaus of standards are all participants in formulating the codes. In some countries the codes are evolved and enforced by the designated government department that deals with public safety.

Boilers along with their mountings and fittings, pressure vessels, and piping are covered together as one body.

The boiler codes comprehensively deal with safety aspects in all areas of boilermaking and operation including boilers for nuclear applications.

• Mechanical design

• Manufacturing and workmanship

• Materials and stresses

• Inspection and testing

• Documentation and marking

• Care and operational guidelines

• Welder qualification

ASME Boiler and Pressure Vessel Committee. The American code for boilers, which is per­haps the most extensively followed code even outside of the United States and Canada (where its use is mandatory), was developed under the aegis of Boiler and Pressure Vessel Committee (BPVC) of ASME, first formed in 1911. The first issue of ASME BPVC was in 1915 and was titled Boiler Construction Code 1914 edition. Today it has its sections developed by three subcommittees working on

1. Components books for power, nuclear, and heating boilers and pressure vessels

2. Service book for materials, nondestructive examination, welding, and nuclear in­service inspection

3. Technology for design, safety valve requirements, boiler and pressure vessel accred­itation, and nuclear accreditation

The ASME Boiler and Pressure Vessel (BPV) Code of 2007 has 12 sections as shown in Table 1.10.

Piping. The ASME code for pressure piping B 31 is divided into several sections covering power, fuel gas, chemical plant, refrigeration, and so on. B 31.1 is the most relevant section for power engineers.

National Fire Prevention Association (NFPA). ASME Boiler and Pressure Vessel (BPV) codes do not deal with firing equipment or burner management systems, which are equally important for boiler safety. They are covered by the design rules evolved by NFPA. There are more than 300 code books published by NFPA covering all possible areas where fire hazard can be present.

Sections of American Society of Mechanical Engineers Boiler and Pressure Vessel Committee 2007

No.

Section

I

Rules for construction of power boilers

II

Materials, Parts A-D

III

Rules for construction of nuclear facility components, Parts 1-3

IV

Rules for construction of heating boilers

V

Nondestructive examination

VI

Recommended rules for care and operation of heating boilers

VII

Recommended guidelines for care of power boilers

VIII

Rules for construction of pressure vessels

Div. 1

Pressure vessels

Div. 2

Pressure vessels—alternative rules

Div. 3

Alternative rules for construction of high-pressure vessels

IX

Welding and brazing qualifications

X

Fiber-reinforced plastic pressure vessels

XI

Rules for in-service inspection of nuclear power plant components

XII

Rules for construction and continued service of transport tanks

Note: Leading boiler codes of other countries also cover these aspects. Perhaps the ASME code is the most comprehensive, besides being regularly updated every 3 years.

However, the code applicable to boilers is only NFPA 85, titled Boiler and Combustion Systems Hazards Code, whose purpose is to contribute to operating safety and to prevent uncontrolled fires, explosions, and implosions in equipment as described in Section 1.1.

This code is applicable to

• Single burner boilers

• Multiple burner boilers

• Stoker-fired boilers

• Atmospheric fluidized-bed boilers with a fuel input rating of 3.7 MWth (12.5 million Btu/h) or greater

• Pulverized fuel systems

• Fired or unfired steam HRSGs

Documents referenced within this code are considered part of the requirements of NFPA 85. These are given in Table 1.11.

Boiler auxiliaries. The design rules for boiler auxiliaries are not specified, unless they are pressure holding. The valves, mountings, and fittings are covered by ASME BPV code but not the fans, AHs, mills, etc. For these auxiliaries, design rules are not mandated by codes but ASME PTCs are available.

Performance test codes. ASME PTC, as the name suggests, defines testing of auxiliary equipment for acceptance purposes. These codes cover all equipment in a power plant including boiler, HRSG, aH, mills, steam purity, etc. Table 1.12 lists more than 21 PtCs that are relevant to boiler engineers.

National Fire Prevention Association Codes Relevant to Boilers

Code

Title

Edition

85

Boiler and combustion systems

Hazards code

30

Flammable and combustible liquids code

2003

31

Standard for the installation of

2001

Oil-burning equipment

54

National fuel gas code

2002

69

Standard on explosion prevention

2002

Systems

70

National electrical code

2002

PTC

Year

Title

4

1998

Fired steam generators

4.2

1969 (R1997)

Coal pulverizers

4.3

1968(R1991)

Air heaters

4.4

1981 (R1992)

Gas turbine heat recovery steam generators

6

1996

Steam turbines

6A

2001

Test code for steam turbines—appendix to PTC 6

6-S

Procedures for routine performance test of steam turbines

8.2

1990

Centrifugal pumps

11

1984 (R1995)

Fans

12.3

1997

Deaerators

19.1

1998

Measurement uncertainty

19.2

1987 (R1998)

Pressure measurement

19.3

1974 (R1998)

Temperature measurement

19.7

1980 (R1988)

Measurement of shaft power

19.8

1970 (R1985)

Measurement of indicated power

19.10

1981

Flue and exhaust gas analyses

19.11

1997

Steam and water sampling, conditioning, and analysis in the power cycle

21

1991

Particulate matter collection equipment

22

1997

Performance test code on gas turbines

25

1994

Pressure relief devices

36

1998

Measurement of industrial sound

38

1980 (R1985)

Determining the concentration of particulate matter in a gas stream

46

1997

Overall plant performance

PM

1993

Performance monitoring guidelines for steam power plants

TABLE 1.12

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