ASME B31.3 covers process piping, but what is within the scope of piping? This is defined in the Code in the definitions part of Chapter I.
A piping system is defined as follows.
Interconnected piping subject to the same set or sets of design conditions. Piping is defined as follows. Assemblies of piping components used to convey, distribute, mix, separate, discharge, meter, control, or snub fluid flows. Piping also includes pipe-supporting elements, but does not include support structures, such as building frames, bents, foundations, or any equipment excluded from this Code (see para. 300.1.3).
Piping includes piping components, which are defined as follows.
Mechanical elements suitable for joining or assembly into pressure-tight fluid-containing piping systems. Components include pipe, tubing, fittings, flanges, gaskets, bolting, valves, and devices such as expansion joints, flexible joints, pressure hoses, traps, strainers, in-line portions of instruments, and separators.
Piping also contains pipe, which is defined as follows.
A pressure-tight cylinder used to convey a fluid or to transmit a fluid pressure, ordinarily designated pipe in applicable material specifications. Materials designated tube or tubing in the specifications are treated as pipe when intended for pressure service.
These definitions should be reviewed when determining whether something is within the scope of the Code. Some examples follow.
There is often some confusion as to whether instrumentation is covered by the Code. However, the definition of piping components makes it clear that in-line portions of instruments are included in the scope and must comply with ASME B31.3 rules. Often, they are qualified as unlisted components (see Section 4.1 and 4.15).
With respect to piping supports, the supporting elements such as shoes, spring hangers, hanger rods, sway braces etc. and their attachments to the structure (the definition of pipe-supporting element in the Code includes the structural attachment) are included in the scope of ASME B31.3. However, the structures to which they are attached are not