Evaluation of growing corrosion

In the challenging terrains of Southwest China’s W shale gas field, several natural gas gathering pipelines ranging from 8 in. - 20 in. were constructed with significant elevation changes and numerous bends, with a minimum bend radius of 1.5D. The medium inside these pipelines, comprising water-bearing shale gas, introduces internal corrosion as a fundamental challenge to the gas field’s pipeline system. It is well known that microbiologically influenced corrosion (MIC) and CO2 corrosion are the common types of corrosion in shale gas fields. To ensure the safe operation of shale gas pipelines, it is crucial to monitor the trend of internal corrosion growth, understand the corrosion growth rate, and assess the effectiveness of existing corrosion control measures.

Over 70% of the pipelines in this gas field are equipped with pigging valves for launching pipeline cleaning devices, such as foam pigs and mandrel pigs with or without wire brush. With the given low daily gas throughput in some pipelines, selecting internal inspection technologies compatible with pigging valves presents a challenge for the pipeline inspection engineers. The PIGPROX inline inspection (ILI) technology utilises patented eddy current sensor technology. This ILI technology is specifically designed for detecting internal corrosion defects. The PIGPROX design resembles that of a cleaning pig, characterised by its short length, light weight, and flexible navigability, making it compatible with pigging valves for easy deployment.

PIGPROX ILI operation

The five shale gas lines shown in Table 1 were inspected two times by PIGPROX ILI tools in 2022 and 2023.

Among these five shale gas pipelines, three pipelines utilised pigging valves for launching, whilst the other two pipelines utilised the standard pig launching barrels. The pipeline with the highest average operational velocity reaches up to 3 m/sec., whereas the slowest operates at 0.48 m/sec. The inspection was successfully conducted on all these pipelines, with the first run success rate of 100% and collected good quality data of high signal to noise ratio.

ILI data outcome in 2022 and 2023

Number of defects analysis

The number of internal corrosions detected in 2023 indicated a significant increase, with the growth of new defects ranging between 63.4% and 177.8%. This phenomenon highlights that the growth of internal corrosions has escalated on these inspected pipelines.

Startling internal corrosion growth

Taking A2 pipeline as an example, we did a run comparison of the PIGPROX eddy current inspection data between 2022 and 2023. The analysed data in 2022 and 2023 revealed…

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Read the article online at: https://www.worldpipelines.com/special-reports/17042024/evaluation-of-growing-corrosion/