As explained in Chapter 4, under the heading Distinction Between Boiler Proper Piping and Boiler External Piping, Section I rules for the design of boiler proper piping are somewhat limited. They actually cover the design of pipe for internal or external pressure only. More extensive rules are provided in B31.1, Power Piping Code, applicable to the design of boiler external piping. Those rules cover, in addition to pressure, many other loads that piping might be subject to, such as mechanical loads that may be developed due to thermal expansion and contraction of the piping, impact loading, gravity loads, and seismic loads. Although such comprehensive rules are not provided by Section I for the design of the boiler proper piping, the boiler manufacturers over the years have managed to design this piping so that it serves its purpose in a satisfactory manner, often using design methods of B31.1. Designers of boiler piping, whether boiler proper piping or boiler external piping, are thus faced with a mixed bag of interrelated rules and should be aware of a number of special provisions and potential pitfalls that need to be considered. These are discussed in the following sections of this chapter.

Boiler external piping and boiler connections are described in PG-58. There are about 20 paragraphs explaining and defining BEP systems for drum-type boilers, isolable and separately fired superheaters, multiple boilers connected to a common steam header, high-temperature water heaters and forced flow steam generators. Section I provides five figures showing the schematics of the Code jurisdictional limits of piping for various piping systems.