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51318-11345-Effectiveness of Shorter Corrosion ILI Re-inspection Interval with varied ILI technologies:Finding the Unexpected High Corrosion Growth Rate of External Corrosion and MIC on Tape Lines.

The authors have identified high corrosion growth rate (CGR) features during excavation on one of the polyethylene tape coated lines by running more frequent corrosion in-line inspection tool runs.

Product Number: 51318-11345-SG
Author: Jiajun (Jeff) Liang / Michael Holm / Gordon Fredine / Yanping Li
Publication Date: 2018
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 Most pipeline operators are using back-to-back In-line Inspection (ILI) tool runs to calculate corrosion growth rate (CGR). The CGR is used to predict the remaining life of pipe based on identified corrosion features. This methodology can be problematic as corrosion is a stochastic (non-linear) process. CGR can be higher due to unexpected factors involved with the operation of the pipeline that include, but are not limited to, heavy rain fall, increased operating temperature and changing soil condition due to excavation. Moreover, predicting remaining life on polyethylene (PE) tape coated lines is made more difficult due to potential shielding of the cathodic protection (CP). If CP is not effective enough to prevent the corrosion process, back-to-back or signal-to-signal CGR from the previous inspections can only be representative of past operational conditions and not for the future prediction.

The authors have identified high CGR features during excavation on one of the PE Tape coated lines by running more frequent corrosion ILI tool runs. The previously calculated CGRs were relatively low over the past decade for the pipeline. During the excavation, soil sample collection results showed that the pipeline suffered external corrosion due to general corrosion and microbiologically influenced corrosion (MIC). Identification of MIC as a corrosion threat was not consistent with previous operation and field findings for this pipeline. After confirming these results with several other excavation sites, the integrity program for the pipeline was adjusted and future ILI corrosion runs were selected based on varied corrosion ILI technologies and more frequent ILI tool runs to properly assess and predict the growth rate of these features. This paper summarizes the field findings and the adjustments to the pipeline’s integrity program based on the findings (i.e., MIC) including the methodology for varied ILI tool runs.

KEYWORDS: Corrosion growth rate, CGR, in-line inspection, ILI, metal loss, PE tape, microbiological influenced corrosion (MIC), threat management, re-inspection interval, cathodic prediction

 

 

 Most pipeline operators are using back-to-back In-line Inspection (ILI) tool runs to calculate corrosion growth rate (CGR). The CGR is used to predict the remaining life of pipe based on identified corrosion features. This methodology can be problematic as corrosion is a stochastic (non-linear) process. CGR can be higher due to unexpected factors involved with the operation of the pipeline that include, but are not limited to, heavy rain fall, increased operating temperature and changing soil condition due to excavation. Moreover, predicting remaining life on polyethylene (PE) tape coated lines is made more difficult due to potential shielding of the cathodic protection (CP). If CP is not effective enough to prevent the corrosion process, back-to-back or signal-to-signal CGR from the previous inspections can only be representative of past operational conditions and not for the future prediction.

The authors have identified high CGR features during excavation on one of the PE Tape coated lines by running more frequent corrosion ILI tool runs. The previously calculated CGRs were relatively low over the past decade for the pipeline. During the excavation, soil sample collection results showed that the pipeline suffered external corrosion due to general corrosion and microbiologically influenced corrosion (MIC). Identification of MIC as a corrosion threat was not consistent with previous operation and field findings for this pipeline. After confirming these results with several other excavation sites, the integrity program for the pipeline was adjusted and future ILI corrosion runs were selected based on varied corrosion ILI technologies and more frequent ILI tool runs to properly assess and predict the growth rate of these features. This paper summarizes the field findings and the adjustments to the pipeline’s integrity program based on the findings (i.e., MIC) including the methodology for varied ILI tool runs.

KEYWORDS: Corrosion growth rate, CGR, in-line inspection, ILI, metal loss, PE tape, microbiological influenced corrosion (MIC), threat management, re-inspection interval, cathodic prediction