Abstract
The RRP pipeline company operates a network of crude oil and oil product pipelines in The Netherlands and Germany and refined product storage facilities. The oil is transported to refineries in Germany, while other lines transfer refined products sourced from refineries in the Europoort area.
One of the pipelines was known to be subjected to movement due to mining activities which caused land subsidence. Although the mining activities started after pipeline construction, these were foreseen, and considerations were made during the design phase of the pipelines. The conscious decision was made to align the right of way with the mining area, and a system of strain gauges was installed at specific monitoring points. Strain gauges were installed to monitor the influence of the mine on the pipeline and assumed to provide absolute levels of axial strain in more than one hundred locations. Strain gauge data is collected regularly and compared to a model of the pipeline to monitor the influences of ground movement on the axial loading of the line. Pipeline strain relief operations are performed as needed, where the line is excavated, and partially renewed for relaxation.
Although the system continues to work about 60 years after installation, it does not cover the entire length of the pipeline. During regular technical exchanges with NDT Global, the idea was discussed to consider a newly developed technology to measure axial strain by means of ILI tool in pipelines.
Eddy current testing is widely used as an NDE inspection technique for ferrous and non-ferrous materials. Eddy current sensors are commonly used for ID/OD discrimination on MFL tools, and widely known to be most sensitive for diagnosis of surface-breaking defects. The technology is highly mature when deployed in various applications, for instance for pipelines in-ditch inspections during validation activities.
RRP and NDT Global agreed to use the Eddy Current inline inspection strain measurement to capture data for the full length of the line and compare this data to the measurements from the strain gauges installed on the pipelines.
This paper will summarize this validation activity and present the latest effort in developing eddy current for in-line strain measurement in pipelines. The fundamental physical principles will be reviewed, and key parameters considered during the design. Internal validation steps and results will be highlighted. A particular focus applies to the analysis of a known and well-characterized geohazard event.
The authors will evaluate the advantages and disadvantages of the various technologies and discuss how new technologies can be used to improve the integrity of pipelines facing geohazards.
