Secondary Process Piping
Process piping located downstream of a block valve that can be valved-off without significantly affecting the process unit operability is commonly referred to as secondary process piping. Often, secondary process piping is small-bore piping (SBP).
Source: API 570, Piping Inspection Code: In-service Inspection, Rating, Repair, and Alteration of Piping Systems, Fourth Edition, February 2016, with Addendum May 2017. Global Standards