ABSTRACT

Pipelines are energy lifelines, networks that deliver the nation's petroleum products within the country and across the borders. However, pipelines do deteriorate over the time. Detailed Integrity Assessment of one such veteran pipeline is carried out, having passed seven decades in operation while commissioned in 1945. This paper discusses the assessment challenges, inspection findings and recommendations given to keep this old offshore/onshore unpigable giant in service.

Using the complex geometry of the different pipeline sections (pigable and unpigable); Hazard Identification studies (HAZID), Internal Corrosion Direct Assessment (ICDA) and External Corrosion Direct Assessment (ECDA) have been modified for both offshore and onshore unpigable sections. ICDA methodology has been modified in view of environmental, operational and inspection data along with flow modeling study. The ECDA approach is modified for offshore sections by managing risk of the pipeline corrosion failures while minimizing the cost required for verifications and repairs. Direct examination of these locations has been carried out followed by statistical evaluation of results. The offshore pipeline section stability has been ensured in view of free span analysis. Recommendations pertaining to internal and external corrosion control have been given for the safe operation of the pipeline along with remnant life.

INTRODUCTION

The pipeline was constructed in 1945 and comprises of three sections:

  • A 20/22-inch onshore section, which was re-routed in 1969, and runs from the pump station to a location 17.6 km downstream. This section of the pipeline can be inspected internally by inline inspection tools. This section is externally protected by an impressed current CP system.

  • An 18-inch offshore tie-in section. This connects the onshore section to the offshore section, and runs from 17.6 km to 22.2 km. This section of the pipeline was re-routed in 1969.

  • Two 12-inch offshore sections, which run from 22.2 km to 49.1 km and continue onshore till the refinery at 65.98 km.

Keywords:
Subsurface Corrosion, inspection, materials and corrosion, Upstream Oil & Gas, Pipeline Corrosion, well integrity, flowline corrosion, riser corrosion, corrosion rate, wall thickness
Subjects:
Pipelines, Flowlines and Risers, Materials and corrosion, Well Integrity, Subsurface corrosion (tubing, casing, completion equipment, conductor)
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2017. NACE International
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