Piping

Introduction:

The term fabrication applies to the cutting, bending, forming, and welding of individual pipe components to each other and their subsequent heat treatment and nondestructive examination (NDE) to form a unit (piping subassembly) for installation. The term installation refers to the physical placement of piping subassemblies, valves, and other specialty items in their required final location relative to pumps, heat exchangers, turbines, boilers, and other equipment; assembly thereto by welding or mechanical methods; final NDE; heat treatment; leak testing; and cleaning and flushing of the completed installation. Depending on the economics of the particular situation, fabrication may be accomplished in a commercial pipe fabrication shop, or a site fabrication shop, where portions of the piping system are fabricated into subassemblies or modules for transfer to the location of the final installation. As a general rule piping NPS 21⁄₂ (DN 65) and larger for nuclear and fossil power plants, chemical plants, refineries, industrial plants, resource recovery, and cogeneration units are most often shop fabricated. Piping NPS 2 (DN 50) and smaller is often shop fabricated where special heat treatment or cleaning practices may be required; otherwise it is field fabricated. Pipelines and other systems involving long runs of essentially straight pipe sections welded together is usually field assembled. In recent years, the infusion of new bending technologies, new welding processes, new alloys, fracture toughness limitations, and mandatory quality assurance (QA) programs have made piping fabrication and installation much more complex than in the past. Greater emphasis is being placed on written procedures for QA and quality control (QC) programs, special processes, and qualification and certification of procedures and personnel. Improper selection of fabrication or installation practices can result in a system, which will not function properly or will fail before...