A decision should be taken at the design stage either to use expensive corrosion resistant alloys (CRA) or carbon steel. This decision may be based on field experience, on the evaluation of a particular material for a given environment, or on modeling. Selection of CRAs increases capital expenditure (CAPEX), whereas selection of carbon steel increases operational expenditure (OPEX). Thus, during the design stage, a balance between CAPEX and OPEX is established. In either case, implementation of appropriate mitigation activities is required. This chapter discusses some time-tested and proven activities to mitigate internal corrosion, including pigging, corrosion inhibitors, biocides, internal linings and coatings, cladding, cathodic protection, and process optimization.

Mitigation – Internal Corrosion

The most severe operational hazards of pipelines are the risks associated with the transportation of multiphase fluids. When water, oil, and gas are flowing simultaneously inside the pipeline, there are quite a few potential problems that can occur. A main challenge that engineers face is, thus, how to design and install the pipeline and transmission system to assure that the multiphase fluids will be safely and economically transported from well locations all the way to the downstream processing plants. This chapter outlines major procedures of pipeline precommissioning and testing, including pipeline flooding, cleaning, gauging operations, pipeline hydrotesting, leak testing, pipeline dewatering, drying, and purging.

Pipeline Precommissioning and Testing

From its fabrication to start-up, a pipeline system has to pass a series of tests. Some of these, such as the factory acceptance test (FAT), are done onshore at the fabrication yards with individual components. The FAT mainly consists of the inspection, testing, and reporting of the system according to the drawings, specifications, and requirements of the contract. Pipe sections must pass the FAT before they are accepted. Some of the tests, such as the pipeline hydrotest, are mainly done offshore with either a portion of the whole pipeline system or the whole pipeline system. The hydrotests are conducted to check the mechanical strength of the pipeline system and the integrity of the connections. The hydrotest is one of the pipeline precommissioning activities. Precommissioning is performed after the pipeline system is installed, and all the tie-ins are completed to assess the global integrity, qualify the system as ready for commissioning and start-up, confirm the safety to personnel and environment, and confirm the operational control of the pipeline system. This chapter covers the main activities associated with subsea pipeline testing and pre-commissioning.

Pipeline Testing and Precommissioning

The first phase of the Zeepipe development included a 814-km (506-mile), 40-in gas pipeline from the Sleipner Field in the Norwegian North Sea to Zeebrugge, Belgium The pipeline, which is more than twice as long as the next largest single-section offshore pipeline in the world, was constructed and commissioned in 1991--1993 Commissioning concepts developed for Zeepipe included a sophisticated pipeline de-watering method and a novel high-pressure gas drying concept The successful operations during start-up of the Zeepipe pipeline have set new standards for commissioning long-distance gas pipelines On the basis of the Zeepipe experience, pigging and commissioning of coated pipeline sections more than 1,000 km (620 miles) long is feasible without expensive intermediate pigging stations The Zeepipe is internally coated with epoxy to reduce pipe wall roughness and minimize corrosion during storage and construction The high-pressure drying concept eliminates flaring of drying gas, reducing the environmental impact, and significantly shortens commissioning time This allows gas deliveries to begin immediately after the dewatering operation is completed The corrosion inhibition method used resulted in lower chemical consumption than with conventional techniques, reducing costs and environmental problems

Stavanger S

Papers

Commissioning the Zeepipe system sets new standards