Optical in-line inspection tool for internal monitoring of pipelines
Feb 10, 2006
This article will introduce a new range of opto-electronic in-line inspection tools. The technology incorporated into the tool includes a laser-based 3D-imaging technology providing enhanced resolution and detection capabilities for the inspection of the internal surface of a pipeline.
The requirement for accurate and reliable inspection systems for pipelines is growing. Pipeline operators need to have access to precise information regarding the state of their networks in order to optimize maintenance procedures and usage of their pipeline systems. A critical set of data is the geometric information regarding possible anomalies and flaws in the wall of the pipe, including internal metal loss. Measurements of length, depth, width and location are needed in order to perform integrity assessment and fitness-for-purpose studies.
- Extending the use of existing pipelines beyond their original design life,
- Upgrading existing pipelines in order to increase throughput,
- Inspection needs regarding the combination of older and newer pipelines of different sizes in a wider infrastructure such as the North Sea,
- The inspection of previously termed "unpiggable" pipelines,
- Precise internal inspection data for offshore pipelines,
- Inspection of telescopic lines, i.e. pipelines of dual- or multi-diameter design.
Pipelines with varying diameter or nonconstant diameter have emerged as a result of "smart" design, i.e. allowing changes in size for one or the combination of the following reasons: smaller size platform risers on offshore systems in order to save weight and costs, smaller size main valves in a large diameter line in order to save weight and thus costs and step changes in the diameter of gas pipelines to account for the inverse relation between volume and pressure.
Tool | Mission | Physical Principle Used |
---|---|---|
Caliper Tools | detection, sizing, location of geometric anomalies | mechanical, magnetic induction |
Metal Loss or Corrosion Detection Tools | detection, sizing, orientation, location of metal loss features | magnetic flux leakage (axial and transverse), ultrasonics, eddy current |
Crack Detection Tools | detection, orientation, location of cracks, where possible also sizing. | ultrasonics |
Inertia Tools | Mapping, pipeline displacement | gyroscopes |
The tool being introduced here can be applied in a large variety of different types of pipelines, however initially the major focus regarding its application were offshore gas pipelines. The total length of offshore pipeline infrastructure is growing continuously. In the Norwegian sector of the North Sea alone over 7000 km of high pressure pipelines were taken into operation since the 1980's, mainly in the diameter range from 16“ to 42“. These pipelines are inspected regularly and maintained with greatest care. The range of specialized equipment used for this task, usually referred to as in-line inspection tools, includes technology utilizing a variety of non-destructive testing principles, for instance magnetic flux leakage and ultrasound.
The opto-electronic tool has been designed to provide an accurate and cost-effective solution for the inspection of the internal surface of pipelines and consists of a highly compact optical system built into a suitable mechanical pig frame. As with other in-line inspection tools the mechanical components must incorporate a drive unit, house the energy supply and provide room for the measurement and data storage devises.
The inspection tool is fully autonomous, carrying onboard battery power and all necessary computer hard- and firmware. The laser based line scan technology is extremely power and data friendly making it possible to cover inspection ranges of up to 1000 km for the larger size tools, traveling at 5 to 10 m/s. The general mechanical design of the tool makes it suitable for use in telescopic lines, i.e. pipelines with varying diameter.
In order to make sure that all the optical lenses and orifices are kept clean, a permanent flow of gas is induced across the length of the tool due to the differential pressure across the tool. Any dirt or debris, due to dust or sediment in the gas transported is thereby kept from settling on the tool.
Data recorded during a survey can be displayed immediately after a run has been completed and are easy to interpret. What you see is what you have, as can be seen clearly in Figure 3a and Figure 3b. This technology provides a very direct and quick means to assess the state of the internal surface of a line inspected. The data analysis software includes a variety of viewing options.
Any anomalies are initially viewed by simply "surfing" through the pipeline. Viewing options include 2D- and 3D-representation as well as wire-frame configurations. The latter enable a detailed inspection of the pipe and the sizing of any flaws found. Figure 3a shows a regular photograph of an anomaly on the surface with a diameter of 25 mm. Figure 3b shows the same defect as seen by the tool and presented in a 2D mode.
The optical and electronic system of the tool works with a depth resolution of 1 mm and a minimum defect size (area) of 2 x 2 mm. The optical resolution of the image is thereby better than 1 x 1 mm. The available mechanical adaptation kits enable the tool to be used for any nominal pipeline diameter from 10“ through to 52“. The design incorporates the ability of the tools to inspect multi-diameter pipelines.
Inspection speeds of up to 5 m/s in gas and operational pressures of up to 200 bar can be accommodated. The tools are fairly light weight. For instance the weight of a 40“ configuration for the inspection of a 100 km pipeline is only approximately 70 kg. Figure 4 and Figure 5 show a CAD drawing and a photograph of the 42“ configuration of the tool.
The opto-electronic tool has been used for a number of inspection projects to date including a positive "Factory Acceptance Test" (FAT) by DNV. The tool fully complies with a number of technical requirements placed upon it:
- high sensitivity and measurement accuracy regarding internal anomaliesand flaws,
- internal corrosion/metal loss as well as any type of internal anomaly including geometric changes are detected and sized with a very high resolution,
- data access and data review are possible at site immediately after an inspection run,
- the tool has a full multi-diameter capability including the ability tonegotiate diameter reduction (bore restrictions) of up to 50 %.
The design of the device makes it well suited also for the inspection of non nonstandard pipelines. These types of lines, which are not normally suitable for the inspection with free-swimming tools are also sometimes referred to as "non-piggable" lines. Due to its mechanical flexibility the opto-electronic pig introduced here can provide valuable information for the integrity assessment of such pipelines.
The tool can be applied as a standalone inspection device or in combination with the use of other in-line inspection tools complementing the information collected during metal loss and crack detection surveys.
[1] Cordell, J., Vanzant, H., All About Pigging, On-Stream Systems, Circencester, 1995
[2] Skerra, B. et al., Handbuch der Molchtechnik, Vulkan-Verlag, Essen, 2000
[3] In-Line Nondestructive Inspection of Pipelines, prepared by NACE International Task Group 039, NACE International Publication 35100, NACE international, 2001
[4] Pipeline Pigging & Integrity Technology, 3rd edition, Editor John Tiratsoo, Scientific Surveys and Clarion, 2003
[5] Specifications and requirements for intelligent pig inspection of pipelines, Pipeline Operator Forum, Shell International Exploration and Production B.V., EPT-OM 1998
[6] Reber, K., Beller, M., How To Get The Most Of The Regular And Repeated Inspection Of Pipelines Using In-Line Inspection Tools, Proceedings of the Sixth International Conference, Pipeline Maintenance & Rehabilitation, PennWell, Berlin, 2003
[7] Neestas, Ola, New Condition Monitoring Tools For Cost Effective Pipeline Integrity Assurance, Proceedings of the 2nd Petro- Min Pipeline Conference, PetroMin, Singapore,2003
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