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IT3 System Renews 25 Mile Pipeline

  • System: 2" PVC / 3" Steel
  • Pressure: 135 psi
  • Temp.: 110° F
  • Fluid: Multiphase Hydrocarbon
  • Length: 25.5 miles
  • Installed: 1975
  • Location: Baker, Montana
  • Owner: Shell Oil Company

HISTORY
In the early sixties Shell began production in their Montana fields, and by 1974 five of these units were experiencing leaks in the steel flow lines. Furthermore, many lines were designated critical in terms of present mechanical integrity and future environmental considerations for the surrounding area - part of the Little Missouri River Basin.

The fields produce a multiphase hydrocarbon with approximately two percent H2S and CO2. Water cuts averaged 55% and chloride contents varied 20,000 to 50,000 ppm. Paraffin build-ups created further operating difficulties causing downtime for pigging and costly chemical treatment. Some lines averaging three leaks a year. The majority of the flow lines were 3 inches in diameter. (There were approximately 2.6 miles of 4-inch included.) The average operating pressures ranged from 50 to 135 psi, but pressures could cycle in excess of 400 psi. Temperatures varied between 70°F and 110°F.

SOLUTION
After evaluating alternatives, Shell contacted Unisert Systems to install the patented IT3 Multi-layer Pipeline System using 2" PVC in the existing 3" steel lines. The project consisted of 40 different lines in five fields: Little Beaver, 51,056'; Cedar Creek, 31,162'; Coral Creek, 29,630'; South Pine, 16,880'; and Pennel, 6,030' for a total of 134,758'.

The repair project was carefully scheduled over a sixteen month period to allow Shell to meet production requirements. Since Unisert was faced with maintaining a minimal downtime, each line was not shut-in for repair until all possible preliminary work had been done. The two primary installation considerations were the numerous bends and elbows indicated by the line profile and the heavy rains, since neither men nor equipment were effective in "knee-deep" mud. Flexibility in IT3 design enabled the engineers to work in all but the most extreme weather with optimum segment lengths between elbows. The slower the work of reconnecting the system was kept to a minimum.

2.36 O.D. PVC was selected as the liner since it was the most economical plastic pipe that could still maintain chemical resistance to the fluids. The first segment was completed in April 1974 in the Little Beaver Field. Standard IT3 installation procedures were used. However, in order to remove all traces of paraffin, the lines had to be hot oiled, pigged, and then sized to ensure a smooth liner insertion.

RESULTS
The total 25.5 mile project was completed in August 1975. All lines have been in continuous use with an exceptional maintenance record.

One leak caused by a cement void was located fourteen months after installation. Unisert took steps to correct the problem and now offers a cement bond log as verification of a continuous cement sheath.

The savings to Shell have been significant not only in terms of the initial installation (60% of the replacement cost of steel), but also in decreasing long term operating costs. The added expense of periodic chemical treatments and shutdowns to pig the line and remove paraffin has been eliminated.

 

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