Rules for the Process Piping Code Section B31.31 have been developed considering piping typically found in petroleum refineries; chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and related processing plants and terminals. This Code prescribes requirements for materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of piping. his Code applies to piping for all fluids, including: (1) raw, intermediate, and finished chemicals; (2) petroleum products; (3) gas, steam, air, and water; (4) fluidized solids; (5) refrigerants; (6) cryogenic fluids . Also included within the scope of this Code is piping which interconnects pieces or stages within a packaged equipment assembly.