ABSTRACT

The GreenStream pipeline is the longest underwater pipeline ever laid in the Mediterranean Sea. The primary objective of pipeline integrity management (PIM) is to maintain pipelines in a fit-for-service condition while extending their remaining life in the most reliable, safe and cost effective manner. The objective of a corrosion management plan is to define all necessary activities to assure the integrity of the pipelines by control of corrosion. This will ensure consistent availability and safe operation of the transmission pipelines throughout the specified design life.

Under these circumstances, it has become crucial to manage operational risk through the use of effective technology and best practices for inspection and maintenance planning. This paper presents the experience of corrosion management of GreenStream pipeline through corrosion mitigation, corrosion monitoring and inspection strategy used in Mellitah Oil & Gas BV.

External corrosion on GreenStream pipeline is controlled with a combination of coatings and cathodic protection while internal corrosion is controlled with a combination of chemical inhibitors, periodic cleaning, internal lining and process control. The monitoring and inspection techniques provide a way to measure the effectiveness of corrosion control systems and provide an early warning when changing conditions may be causing a corrosion problem.

This paper describes corrosion management system used in Mellitah Oil & Gas BV for its natural gas export pipeline based on standard practices of corrosion mitigation and inspection.

INTRODUCTION

The GreenStream pipeline is an offshore pipeline laid in the Mediterranean Sea. It is 516 km long natural gas pipeline which has 32 inches diameter. It runs from Mellitah in Libya to Gela in Sicily, Italy. It was constructed with initial capacity of 8 billion cubic meters (bcm) of natural gas per year. Later the capacity of the pipeline was increased to 11 bcm. The pipeline parameters are given in Table -1.

Maintaining pipeline in a safe and reliable condition is one of the major tasks for pipeline owners and operators. Assuring safety and reliability of a pipeline demands an integrated and efficient integrity management system. Pipeline integrity management is a process for assessing and mitigation pipeline risks in order to reduce both the likelihood and consequences of incidents. The U.S. Office of Pipeline Safety (OPS) has established1 a set of regulations impacting operators of hazardous liquids and natural gas transmission lines. Part of the mandate is the development of a comprehensive integrity management program to address ongoing pipeline safety. Other international references related to pipeline integrity management are:

  • ASME B31.85 - 2012: Managing System Integrity of Gas Pipelines2

  • UK Pipelines Safety Regulations3

  • Pipeline Risk Management Manual - by Muhlbauer4

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