The Code includes three Categories of fluid service, which provides a means of discriminating among possible degrees of hazard. Less stringent design, examination, and testing are permitted for fluid service of lower hazard (Category D) and more stringent requirements are applied for more hazardous fluid service (Category M). All fluid services are considered Normal unless the owner designates them as Category D or Category M.
It is the owner's responsibility to select the fluid service category. Selections of Category D or Category M cannot be made without the owner's permission. The fluid service is assumed to be Normal Fluid Service unless a different selection is made. Because some owners may not be familiar with this responsibility, the piping designer should inform the owner of the responsibility and may offer advice with respect to the selection process.