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Integrity Management of Buried Cooling Water Pipelines

Introduction

Assessing the integrity of a buried structure can prove challenging because of difficulties in accessing the surfaces of the structure. As a result, it is critical for pipeline integrity management that a solution is found to reduce the uncertainty and deliver the most accurate results.

TWI was contacted to find a solution for assessing the integrity of two pipelines buried beneath 3 metres of concrete coating. Due to the type and thickness of the coating, the external surfaces of the pipes were not accessible plus, since measurement of the pipe’s cathodic protection (CP) efficiency was impossible, there were concerns over the likelihood and severity of external corrosion damage on both pipelines.

We provided a comprehensive structural integrity assessment for the two pipelines, providing peace of mind that both pipes were safe to continue service and the current CP system was operating effectively.

To determine the integrity of both pipes, the detailed assessment was conducted using a combination of codes including ASME B31G (2017), ASME B31.8s (2018), API 1160 (2019), and NACE 0502 (2010).

Figure 1. Buried Pipeline
Figure 1. Buried Pipeline

High Value, High-Risk Component

The integrity of these buried pipelines needs to be monitored closely to prevent costly repairs and the severe consequences of failure, including collapsing and leakage. Buried pipelines are subject to issues related to aging, such as excessive wall loss from corrosion (either external or internal), while a lack of confidence in the status of the CP system can raise serious concerns about the condition of the external surfaces of the pipe in contact with the soil.

The recommended solution to address the integrity of external corrosion damage on the pipelines beneath the concrete coating was a thorough, 100% coverage, pulsed eddy current (PEC) inspection followed by an ultrasonic thickness measurement of the reported anomalies.

 

 

Approach

A full-coverage inspection was conducted of both pipelines internally to identify the pipeline conditions against identified threats and damage mechanisms. A number of priority parameters were set during the inspections to make sure the integrity approach was accurate.

Three inspection methods were used concurrently to determine the integrity of the pipes, with an emphasis on the external surfaces, since these are the areas most susceptible to corrosion:

  • Visual inspection (VI):
  • Pulse Eddy Current inspection (PEC)
  • Ultrasonic Thickness Measurement (UTTM)

 

Fitness for Service Assessment

A fitness for service assessment was conducted on the reported anomalies to ensure the pipes are safe to continue in service. As well as carrying out the assessment according to a customised fitness-for-service (FFS) methodology, TWI also provided the client with an inspection strategy for the future, to ensure the most efficient use of resources and reduced inspection costs going forward.

The results of the assessment showed that the pipelines were generally in good condition, despite a few corrosion monitoring locations being identified for NDT inspection at recommended intervals. The conclusion of the results indicates that, while the CP system could not be checked, it is working efficiently on both pipelines and providing an acceptable level of protection and keeping the external corrosion rate below the theoretically expected rate. Inspection intervals of 5 years and 10 years were recommended for the pipelines.

Figure 2. Six Channel Probe
Figure 2. Six Channel Probe
Figure 3. Distribution of the minimum and maximum measured PEC Inspection Results alongside the pipe (inspection zones and quarters)
Figure 3. Distribution of the minimum and maximum measured PEC Inspection Results alongside the pipe (inspection zones and quarters)
Figure 4. Distribution of the remaining wall thickness along the pipe with minimum and maximum measured wall thickness data using UTTM grid scanning at the identified location (reported from PEC inspection)
Figure 4. Distribution of the remaining wall thickness along the pipe with minimum and maximum measured wall thickness data using UTTM grid scanning at the identified location (reported from PEC inspection)
Figure 5. Comparison of Theoretically Estimated Corrosion Rate against the Actual Calculated Corrosion Rate
Figure 5. Comparison of Theoretically Estimated Corrosion Rate against the Actual Calculated Corrosion Rate
Avatar Mehran Izadkhah Senior Project Leader, TWI Central Asia

Mehran joined TWI in 2009. He has managed several projects of risk-based inspection, damage mechanism identification, fitness-for-services, offshore structural integrity assessment, pipeline integrity assessment, corrosion control, cathodic protection, protective coatings, and failure investigations.

He led the development of fully quantitative and semi-quantitative procedures, methodologies, and algorithms utilised in RBI assessment for various assets such as pipelines, boilers, and fixed equipment.

He is now the Global RiskWISE Product Manager, leading and managing the developments of TWI’s RBI and Integrity management software.

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