ABSTRACT

Multiphase transportation of wet natural gas from production wells to treatment facilities exposes pipeline to corrosion risks. Among all types of corrosion attacks, pitting corrosion is the most common cause of failures in gas pipelines. Stochastic nature of pit initiation and growth cast uncertainty on CO2 pitting corrosion prediction. This paper discusses how precipitation of scales and corrosion products on the pipe surface along with other influencing factors contributed to the initiation of pits and finally failure of a wet gas pipeline in a sweet gas field, south of Iran. The technical analysis provided in this study is helpful for further understanding of pitting corrosion in wet gas pipelines.

INTRODUCTION

Oil and gas extraction from reservoirs are to be continued as far as fossil fuels are the most dominate source of the world energy.1 Corrosion is a destructive and cost-bearing phenomenon for every industry dealing with metallic structures. Oil & gas production has been suffering from corrosion since the early history of the industry. Corrosion imposes significant cost of repair and replacement of infrastructures.2,3 Indeed, it forces unplanned shutdowns and causes catastrophic incidents that result in environmental contamination and human casualties. In 2013, NACE has estimated the total costs associated with all types of corrosion at $500.7 billion (3.1% of GDP) in the United States. Corrosion of onshore oil & gas transmission pipelines comprises $7 billion of this total.4 However, the costs associated with corrosion can be reduced significantly if appropriate corrosion mitigation programs are applied.5

Pipeline networks are the main body of all sectors of oil industry including exploration, production, treatment, and distribution. Multiphase pipelines of oil & gas gathering systems are more vulnerable to corrosion phenomena because of complicated water chemistry, presence of acid gas such as CO2 and H2S, multiphase flow, etc. Among all types of corrosion attacks, pitting corrosion is the cause of most failures, especially in wet gas pipelines. Therefore, maintaining pipeline integrity in oil & gas production and gathering systems is a real concern.4-7

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