Development of a 10-in. Piggable Pipeline "Y" Fitting for the Jolliet Project
Authors: Decker L.A. , Tillinghast W.S. 
Published: October 2008

Development of a piggable "Y" fitting for the Jolliet Project is presented and discussed. A development program is presented which includes scale model analysis, full size prototype testing, finite element analysis, strain gage testing and pigging tests on a production "Y". Details of each phase of the program are presented and discussed along with results from pig testing, finite element analysis and strain gage tests.

INTROPUCTION

The Conoco Jolliet Project in the Gulf of Mexico included an oil/water pipeline to connect the Tension Leg Well Platform (TLWP)in Green Canyon Block 184 in 1,760 FSW(536.6 meters) with the Central Processing Platform (CPP) in Green Canyon Block 52 in 616 FSW (187.8 meters). The oil/water pipeline was designed to utilize 10 inch(254.0 mm) inside diameter flexible pipe from the TLWP to a Unified Connection Skid (UCS) located in the northwest corner of Green Canyon Block 184 in 1,020 FSW(311.0 meters). Thereafter, the flexible pipe was extended another 2 miles(3 km) where it connected to a 10.75 inch(273.1 mm) outside diameter steel pipe, transitioned to a 14 inch(355.6 mm) outside diameter and continued on to CPP. Figure 1 shows the pipeline between the TLWP and CPP while Figure 2 illustrates the UCS. As seen in Figure 2, the piping on the UCS also made provision for a 10 inch(nom.) lateral connection for a future tie-in. The oil production from Green Canyon Block 184 was anticipated to have an appreciable amount of paraffin which requires periodic pigging with a scraper-type pig. Although the exact characteristics for the future(lateral) line were unknown, it was decided to design the lateral connection to also provide for passage of scraper pigs. Hence, it was necessary to incorporate a "Y" fitting in the UCS piping that would allow passage of scraper pigs through either of the inlet branches. Moreover, the scraper pig would need to be a dual-diameter to allow scraping of both the 10 inch(254.0 rom) inside diameter flexible pipe and the 14 inch(355.6 mm) outside diameter steel pipeline. It was also decided that the "Y" fitting should be capable of passing 10 inch(nom.) foam-type swab pigs, 10 inch(nom.) soluble spheres and a 10 inch(nom.) dual-diameter(14XI0) gauging pig. Although there have been several "Y" fittings used in the North Sea(16,18 and 20 inch), there have been no underwater applications in the Gulf of Mexico in which pigs more complicated than spheres were used. Because of the smaller pipe size for the Jolliet application and the unique dual-diameter requirements, it was decided to implement a comprehensive development program to design and verify the performance of a 10"XI0"XI0" piggable "Y" fitting. The overall development program is shown in Figure 3. The chart shows seven basic milestones for the program. Figure 3 also illustrates the time associated with each portion of the program.

SCALE MODEL ANALYSIS

A non-symmetric "Y" configuration was initially proposed. The non-symmetric "Y" was believed to offer minimal effect on pigging through the straight side of the "Y". Although the lateral inlet geometry would represent a more difficult configuration to pig(a 30 degree bend), it was not certain that the lateral connection at the UCS would actually require the same extensive pigging as the 10 inch(nom.) line from the TLWP.