Overview of the ASME Boiler and Pressure Vessel Code or BPVC
The American Society of Mechanical Engineers (ASME) was first founded in 1914 to develop standards for boilers and pressure vessels to solve the design flaws that were causing a horrific number of fatal accidents.
The design standards created to prevent similar accidents in the future evolved into the ASME Boiler and Pressure Vessel Code or ASME BPVC. The engineering design standards spelled out in the ASME Boiler and Pressure Vessel Code has been adopted as law in the United States and Canada.
What is in the ASME BPVC?
The ASME BPVC requires significant safety factors to ensure that the boiler or pressure vessel does not yield under expected pressure. Design requirements in the ASME BPVC include but are not limited to the number and dimensions of relief valves, depressurization times and the engineering safety factors to be used in design of the vessels. The ASME Boiler and Pressure Vessel Code also describes what is allowed to happen when fluid or gas is released to prevent over-pressure and rupturing of the pressure vessel.
Pressure vessels must contain pressure safety valves to prevent overpressure, essentially letting the pressure vessel lose some pressure instead of exploding. Ideally, high pressure gasses are routed through pipes to relief vessels. Atmospheric venting is in some operating conditions allowed. However, the over-pressure gas cannot be vented into the atmosphere in a way that creates a fire hazard or toxic conditions. For example, super-heated steam can be vented into the atmosphere if it simply becomes water vapor upon contact with the air and is done in a way that does not endanger employees.
High pressure natural gas cannot be vented to the atmosphere since this can create suffocating conditions and an explosion hazard. For flammable gases, a flare system can be used to control the released gas, burning it instead of letting it vent. For vessels containing liquid, the pressure vessel must permit blow-down or removal of liquid from the pressurized vessel. The liquid can be routed to back up storage tanks, nearby relief vessels designed for that purpose or even a holding pit.
The ASME BPVC is not limited to design requirements. The ASME BPVC section 3 requires traceability of all boilers and pressure vessels. The vessels must be labeled in a way that allows owners to verify its history, location or intended application. Traceability allows failed vessels to be tracked to their manufacturer and prior owners who may have exceeded recommended operating conditions, contributing to the failure.
This overview is by no means complete given the length of the ASME Boiler and Pressure Vessel Code (BPVC). Refer to the ASME Boiler and Pressure Vessel Code (BPVC) standard itself for in depth design requirements.
Sections of the ASME Boiler and Pressure Vessel Code
The ASME Boiler and Pressure Vessel Code is broken into twelve sections. Different sections of the ASME BPVC may apply to storage containers depending on their manufacturing. For example, pressure vessels built to ASME BPVC section 1 for fired pressure vessels or section 8 for unfired pressure vessels may both be used to store flammable and combustible liquids.
Section 1 contains the rules for power boilers. Section II addresses acceptable materials. Section III / Section 3 covers the rules for pressure vessels and boilers used in nuclear power plants. Section IV / Section 4 describes the design rules and standards for heating boilers. Section V / Section 5 outlines the acceptable methods of nondestructive examination such as using ultrasound or radar to inspect weld quality.
ASME BPVC Section VI / Section 6 gives the recommended rules for maintaining and operating heating boilers. Section VII / Section 7 lists the recommended guidelines to taking care of power boilers. These recommendations are not law but strongly recommended by the ASME.
Section VIII / Section 8 describes the standards for Division 1 pressure vessels. Division 1 pressure vessels withstand a pressure greater than 15 pounds per square inch and can be heated or unheated. Section IX / Section 9 gives the standards for welding and brazing qualifications. Welders who want to help build pressure vessels and boilers to ASME Boiler and Pressure Vessel Code (BPVC) standards must be qualified according to the procedures in this section of the ASME BPVC. The ASME BPVC welding standards are different than the welding standards for common piping given in ASME B16.25 for butt-welding pipes that do not carry high pressure and temperature materials like drinking water.
Section X / Section 10 gives design standards for fiber-reinforced plastic pressure vessels. Section XI / Section 11 addresses the rules for in-service inspection of nuclear power plant components. Given the risk of radioactive contamination, Section 11 is separate from the rules for Section 5, even when the some of inspection procedures are similar. Section XII / Section 12 gives the rules for the construction and continued service of transport tanks. Section 12 applies to pressure vessels used to transport dangerous materials at high pressure or very low pressure. The transported materials can include liquid oxygen, liquid natural gas and welding gases kept at high pressure.
In addition to the twelve formal sections, the ASME BPVC contains two sections of code cases. Codes cases are the formal ASME rules for materials and construction methods not covered in the ASME Boiler and Pressure Vessel Code (BPVC). Code cases are also included for boilers and pressure vessels. A separate set of code cases apply to nuclear components. Code cases may be included as part of the formal ASME Boiler and Pressure Vessel Code (BPVC) in a later edition.
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