Underwater Pipeline Inspection

XPLISIT

Pipeline owners in the North Sea normally inspects their pipelines at regular intervals. On the outside the condition of the pipe as well as the close proximity of the pipe are of special interest. Free spans, debris, fish nets and World War II mines are states and objects that will be reported. In the eighties traditonal video cameras and storage on analogue video tape were the state-of-the-art technology giving huge amounts of video cassettes. Some of the oil companies even rented huge barnes to store analogue video tapes.

Back in 1988 Norsk Elektro Optikk (NEO) proposed to use line scan cameras and digital storage for pipeline inspection. The main advantage of this concept was a reduction in the amount of data and the volume requirement of the storage media. A second feasibility study was performed in 1993 and the main development project started in 1994.

Xplisit is a dicontinued product. Below is explained the principle of operation. A total system concept is also shown as well as some of the results.

Line scan camera principle of operation

This figure shows the sensor configuration of a line scan camera (top) and a "normal" video camera (bottom). A video camera has a 2-dimensional array of detectors i.e., pixels while the line scan camera has as its name indicate one line of detectors (pixel). To be able to get a sensible image from a line scan camera, the camera has to be moved relatively to the object to be depicted.

This figure explains how an image is built from individual image lines from the line scan camera. Let's start a time t=1. We then make one exposure of the pipeline i.e., one line of it. We then move the camera 2 mm along the pipe, at t=2 we make a new exposure and get a second image line we put on top on the first line. We then move 2 more mm and make a third exposure and add the third line to the image. We continue this procedure until we have depicted the area of interest. The result is a continuous image, a still image, of the inspected object.

System overview

The Xplisit system had modules both on the ROV and on the surface vessel.

This figure shows the total survey system including the surface vessel and the ROV and the umbilical inbetween. The ROV rolls on the pipeline to achieve smoother movements.

This figure shows camera and light source arrangements. Two light sources per camera. Three cameras, one on top, one on the left and one on the right side of the pipe. The cameras had a resolution of 2 X 2 mm. The light sources were flicker free and illuminated a line of about 50 mm X 1 m at 1 m distance.

This figure shows the Xplisit equipment mounted on the ROV. The camera controller was based on an Intel i960 processor had digital communication with the line scan cameras and sent commands to the lamp power supply via RS232. Data and control signals were sent via an fibre optical link to and from the computer system in the surface vessel. The computer system comprising a custom full size PCI board displayed, compressed and stored data to disk in real time. The custom PCI board had high speed laser based fibre optical link, real time JPEG compression and other functions helping the PC to display data in real time like real time scaling of image data. Due to stability issues Linux was chosen as the operating system of these PCs.

Right side camera and light sources (left image) and ROV with Xplisit system mounted (right image).

Image samples, anomalies

This image shows a part of a pipe with cracked concrete coating.

These images show a free span. The top image shows the pipe from the left side (mirrored to get the bottom down). The middle image shows the pipe from the top camera. The bottom image shows the pipe from the right side as seen from the ROV. As you can see, there is a fish below the pipe (to the left) and obviously we have a free span.

This figure illustrates a free span. A free span is a part of the pipe where the pipe has no support on the seabed. If a free span is too long the pipe might oscillate due to ocean currents like a bridge in a storm and break down. It could also be more exposed to damages from anchors or activities from the fishing industry.

This image shows debris: a fish net and a barrel.

More junk: a bottle and other platics.

Source: http://www.neo.no/research/pipeline/xplisit.html