Based on the assessment process of the data alignment, lab analysis and gas quality, the following was indicated:
The internal corrosion process was caused by the In-service corrosion mechanisms related to product composition and operating condition that promote the formation of internal corrosion processes.
The relationship between metal loss features in relation to the circumferential orientation, the solids extracted, and the elevation profile of the pipe, demonstrates evidence of sediments and liquids accumulation. In addition, the water accumulation of the hydrostatic pressure test and others waste during the construction were able to contribute to the formation of internal corrosion processes.
The rest of the internal corrosions (6%) were isolated and located in a different orientation around the circumference of the pipe (around 12 o'clock position). Therefore, it is not a characteristic pattern of corrosion caused by the accumulation of sediments and liquids. In this order, the following was indicated:
There is no evidence of water condensation that can indicates internal corrosion at the top of the line.
Those Internal corrosion features reported by ILI could have the following causes:
Pre-service corrosion from pipe storage.
Pre-service corrosion from hydrotest water.
Misclassification – Milling or construction related defects.
On the other hand, the inspection reported 2 isolated external corrosion features classified as minor (wt < 20%). Based on the information provided by the client and these anomalies reported, there was no evidence of clusters that could indicate a corrosion process that could represent a risk to the pipeline integrity. This proves that the coating and cathodic protection system of the line were working correctly.
To assess the immediate integrity of the pipe, the corrosion feature were assessed in terms of their axial and circumferential dimensions using Original B31.G Assessment and Kastner respectively, and were considered acceptable for operation (PSafe > MAOP).
To assess the future Integrity, the corrosion growth rate was obtained considering this was the first in-line inspection after the last known inspection and it was used as baseline. A probabilistic assessment was performed, using Monte Carlo simulation with distribution of depth and corrosion starting time, according to indicated by API 1160 with an 90% confidence level, and the internal and external corrosion growth rates were identified.
To determine the effects of growth on the predicted pressures of each anomaly, the Original B31G method was applied to the growing depth estimates. The conservative growth rates were imparted on the depth of all metal loss anomalies described in the last in-line inspection.
All corrosion features were considered acceptable in terms of their axial, circumferential and depth dimensions up to 6 years. According to the future integrity assessment developed, provided that the operating conditions and mitigation activities are implemented against the corrosion growth are maintained (e.g., cleaning plan, corrosion inhibitors, cathodic protection, etc.). (e.g., cleaning plan, corrosion inhibitors, cathodic protection, etc.). In general, all corrosion features were acceptable for operation (PSafe > MAOP).
Based on the Future Repair Plan and the re-inspection Interval developed, the pipeline should be re-inspected in a period no later than 6 years. However, it was recommended adjust the interval re-inspection, considering the pipeline operational conditions, and possible uncertainty on the impact of the current operating condition on the pipe.
Based on the above findings, ANCOR recommended mitigation activities as it's indicated below:
Carry out internal cleaning at most every 6 months, to avoid the growth and formation of internal corrosion processes. Adjust the execution time based on the results obtained if necessary.
Assess the efficiency of the corrosion inhibitors system to understand the characteristics of the system, due to the internal corrosion risk from the presence water as a separate phase in the pipeline and apply the correct concentration to decrease effectively the corrosion rate.
Perform analysis and Interpretation of the corrosion coupons installed on the pipe, to evaluate corrosiveness process, monitor the effect of corrosion mitigation and determine the reaction of the metal to the environment.
Perform annual CP surveys to support the continuous operation of the cathodic protection system and establish historical records and compliance.
Perform the re-inspection of the pipeline in a period not later than July 2025.
