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.

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