ABSTRACT
The pipeline Enhanced Corrosion Management Analysis (ECMA) has been conducted over transmission pipelines that experienced considerable external metal loss after a relative short time in operation. Pipeline historical and current data: pipe design, construction, soil, corrosion control, monitoring, inspection and operational were reviewed and, together with in line inspections (ILI) data, aligned to aboveground surveys and compared to field excavation results. The ECMA methodology proofed to be a cost-effective approach to determine the engineering root causes of the external metal loss identified and to develop adequate short, mid and long term mitigation plans.
INTRODUCTION
Operators of transmission pipelines in the USA, normally limit the scope of their pipeline integrity assessments to identify the threats that may preclude the system to reach the maximum reassessment interval established by the federal or state regulations [1], [2]. The preferred assessment tools are the inline inspections (ILI), also referred to as smart pigs [3]. These ILI tools have evolved over time and increased their accuracy when identifying the location and dimensions of the external metal loss associated to corrosion.
When metal loss due to corrosion is reported by ILI, integrity engineers are able to calculate corrosion growth rates, predict which anomalies may compromise the safe operation of the pipeline system before the next reassessment interval, and execute a repair program to ensure the pipeline operates safely with a designed safety factor.
The procedure described above may be cost efficient for a great number of pipelines exposed to the most common external and internal corrosion under normal operating conditions. However, the integrity of pipeline systems exposed to stray current interference, electrical shielding, or microbiologically influenced corrosion (MIC) may not effectively managed [4]; specially, when the technical root cause(s) of the anomalies are not identified. The pipeline sections that are repaired will be susceptible to the integrity threat when additional mitigation is not implemented. When an Enhanced Corrosion Management Analysis (ECMA) is implemented, the technical root causes of the metal loss due to corrosion may be identified; based on these results short, mid and long term mitigation plans may be implemented to effectively manage the corrosion threat. The case study presented in this document is related to external corrosion.
