The figure above shows the actual guided wave result obtained from one test location on the client's pipeline. The result was processed and analysed by a trained and qualified Level 2 guided wave inspector.
GUL Subsea is based on both GUL Screening and GUL Monitoring technologies, but applied towards subsea pipelines. Therefore, the A-scan and Unrolled Pipe Display can be obtained when performing screening operation using GUL Subsea tools.
The GUL A-scan shows a graph of reflected guided wave amplitudes against pipe distance; zero meters indicates the position of the attached gMAT test location. The dashed lines are known as the distance amplitude correction (DAC) curves, which have been calibrated to allow us to compare the reflection amplitude to the actual cross-sectional area change (CSC) of the inspected pipe.
In general, the signal peaks in the plot that we see, are caused by guided wave reflections from:
- Existing pipe features within the pipe (e.g. welds, supports, flange, bends)
- Defects (e.g. corrosion, erosion)
Typically, an indication or potential defect, is called by an inspector if there is a signal which exceeds the Call DAC (i.e. higher than the blue dashed line) and is localised (the ratio of black to red signals analysed).
The A-scan also shows that the inspection range in this test is approximately 40 meters (131 feet) in both directions of the sensor, or a total of 80 meters (262 feet) .
Unrolled Pipe Display
The Unrolled Pipe Display is a reflection amplitude colour map that plots the circumferential position against pipe distance. The information from this plot gives information about the distribution of the reflected guided wave energy at the circumferential position of any defects and existing pipe features.
This helps inspectors to:
- Distinguish between defect and existing pipe feature
- Detect the circumferential position of a defect
- Estimate the defect depth based on the distribution of material loss
The client was extremely satisfied with the outcome which confirmed that:
- there was no corrosion above allowance reporting threshold;
- the condition of the pipe (internal and external surfaces) was fit for purpose;
- pipe attachments such as CP anodes identified and located;
- wall thickness measurements over 360 degrees at the gMAT position measured the pipe thickness at 6 different circumferential locations. This confirms that the pipe was still close to nominal wall thickness with no variation around the pipe circumference. Hence, ruling out any top or bottom of the line corrosion.
Subsea pipelines are typically in the order of kilometres, with many shorter unpiggable lengths, that should be inspected periodically in order to be confident of their structural integrity. Guided wave screening offers a fast way of assessing pipe condition without the need for disruption to production and because it is non-obtrusive can be done without risk of becoming stuck in the line. Good screening data may allow delaying the interval between pigs runs offering substantial savings both on inspection cost and lost production.
GUL Subsea provides solutions based on guided wave tech, that will help NDT service providers to reliably inspect tens of meters of pipe from a single test location. The solution offers a superior inspection area coverage per test location and can be used to detect location of pipe defects caused by corrosion, erosion or external damage; especially in difficult to inspect areas, such as under concrete weight coat or concrete mattresses or sand/grout bags.
GUL Subsea offers a wide range of diver and ROV deployed solutions, with a strong track record and based on our 21 years of experience in guided wave inspection. Aside from reliable hardware and superior data processing software, audited procedures and GULT training are both important aspects to the success of this inspection work.
For unpiggable lines, GUL Subsea can provide the required integrity information, with which continued safe operation, can be continued in confidence. For piggable lines, the information can be used to supplement pigging data and possibly extend the intervals between pig runs; potentially serving as a cost-effective solution.
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About GUL and GUL Subsea
GUL (Guided Ultrasonics Ltd.
) is an R&D and equipment manufacturing company with headquarters in London, United Kingdom. We provide equipment and consultancy services to NDT service providers. We do not provide periodic-based inspection services directly to pipeline owners.
GUL Subsea is the product line specifically designed for subsea pipe inspection applications. The photo below gives an overview of GUL's main product lines.
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