INNOVATIVE APPROACH FOR A PIPELINE PRE-OPERATION

摘要

"Oleoduto Cabiunas REDUC -OSDUC II", a new 183km 10in pipeline, started operating for TRANSPETRO, a subsidiary of PETROBRAS, in September 2002, transporting Natural Gas Liquids from Cabiunas Terminal, the on-shore facility responsible for treating all natural gas coming from Campos basin crude oil production fields, to a NGL Fractionation Plant (UFL) inside Duque de Caxias PETROBRAS refinery (REDUC), near Rio de Janeiro. Because the NGL delivered from natural gas treatment process was absolutely free of water and considering the high sulfur content in the wet gas coming to shore, the pipeline was designed to be dried with nitrogen, after construction and hydrostatic tests, regardless of pipe materials specifications, in order to prevent corrosion and hydrogen-induced cracking. Commissioning, the next step, could not be performed as a simple and single operation, because the Liquids Recovery Plant (URL), in the first of three development phases, did not have the capacity either to feed main pipeline pump with the minimum flow required to maintain continuous operation or to assure pig run to be performed within the ideal speed range to guarantee good sealing efficiency. After none of the few available alternatives proved to be suitable, there was no doubt that an innovative approach was the only way to overcome the challenges on commissioning the line under such sort of restrictions despite running risks of postponing pipeline startup in case the filling process did not succeed accordingly. Then, TRANSPETRO engineering team came up with an unusual solution where the line fill process was divided into 8 pumping-stoppage cycles along with the use of polyurethane pigs as a mechanical barrier between liquid and gas phases. This work describes all key factors from pipeline conceptual design, to commissioning procedures and implementation, as well as the tools used to forecast flow conditions and all critical events.