To help the reader understand and use the ASME Boiler and Pressure Vessel (B&PV) Code, this chapter for ASME Code Section IV2 (2010 edition) is presented in a simplified manner with the understanding that it is not a Codebook and was not written to replace the Codebook published by the American Society of Mechanical Engineers (ASME).

Although the rules of the ASME B&PV Code, Section IV constitute the minimum requirements for the safe design, construction, installation, and inspection of low-pressure-steam boilers and hotwater boilers (which are directly fired with oil, gas, electricity, or other solid or liquid fuels), they do not cover the operation, repair, alteration, rerating, and maintenance of such boilers. By definition, a low-pressure-steam boiler is a steam boiler in which the operating pressure does not exceed 15 psi (103 kPa), whereas a hot-water boiler is defined as a boiler used for an operating pressure not exceeding 160 psi (1,100 kPa) and/or for a temperature not exceeding 250_F (121_C). Hot-water boilers include hot-waterheating boilers and hot-water-supply boilers. Also covered by the rules of Section IV are potable-water heaters and water-storage tanks for operation at pressures not exceeding 160 psi (1,100 kPa) and water temperatures not exceeding 210_F (99_C).