Note: Descriptions are shown in the official language in which they were submitted.
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Corrosion Assessment Apparatus and Method
BACKGROUND
a. Field of the Invention
This invention relates to an apparatus and a method for assessing corrosion.
In
particular this invention relates to the assessment of corrosion levels on
pipework
in offshore environments.
b. Related Art
External corrosion assessment of pipelines and piping is carried out on both
onshore and offshore installations to determine the level of surface corrosion
present. This information is used to inform maintenance schedules and assess
the fitness for purpose of the structure or asset. This is typically known in
the
trade as fabric maintenance.
The operating companies, of the offshore installations for example, are known
to
have standard corrosion categories which are set by integrity teams within the
organisation. Inspected piping is compared with these standard categories to
give
a measure of the current corrosion state of the pipe. Often this involves
comparing photographs of the current state of the pipes with reference
photographs corresponding to each of the categories. It is known that there is
a
variation in the categories used by different companies but as an example
there
may be four categories corresponding to: (1) no corrosion or surface coating
breakdown, only paint visible, (2) pockets of corrosion visible, limited
surface
coating breakdown (3) connected areas of corrosion and/or surface coating
breakdown, (4) majority of surface covered in corrosion, severe coating
breakdown.
The comparison is typically carried out manually by inspectors and as such can
often be a subjective process. Firstly it is generally necessary for the
inspectors to
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capture photos at selected points of interest around the pipework being
inspected.
This necessarily means that the inspector must choose which parts of the
pipework require further analysis and also must record the location at which
the
photo was taken as well as note any additional information, for example about
the
surrounding pipework or environment. Secondly, the inspector must analyse the
photographs against the category standards in order to produce a maintenance
or
repair report.
This process is both time consuming and subjective, and can therefore be both
expensive and inaccurate.
In addition, many areas of an offshore installation are difficult to access
and
therefore, the requirement to carry and use a camera as well as means to
record
locations and other relevant information, poses a safety risk to the inspector
as he
or she walks and climbs around the installation.
As such it is an object of the present invention to provide a corrosion
assessment
method and system that overcomes the above disadvantages.
SUMMARY OF THE INVENTION
According to the invention there is provided a method of analysing the
corrosion
levels on a surface of a structure, the method comprising the steps of:
- capturing a plurality of digital images including the surface of the
structure,
the images comprising individual frames of a continuous video; and
- analysing each of said plurality of images;
wherein the step of analysing each image comprises:
- selecting an area of interest within an image;
- assigning a number value to each pixel within the area of interest,
the number value corresponding to the colour of that pixel;
- calculating, from the number values of the pixels, a number average
for the image; and
- comparing the number average for the image to a set of reference
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number averages corresponding to a set of standard corrosion levels to
determine a corrosion level for the image.
In order to permit objective comparisons to be made between different parts of
the
structure it is advantageous if the image is thresholded to divide the image
into
regions falling within distinct thresholded limits. Preferably only the area
of interest
is thresholded and then a number value is associated with a range of colours
within the thresholded limits, so as to assign a specific number value to each
pixel.
Typically the area of interest comprises a region of the image comprising the
surface of said structure being analysed, for example the external surface of
a
pipe.
Generally the structure being inspected and analysed comprises more than one
section, for example discrete lengths of pipe between corners or joins.
Preferably
each section is captured in a series of images or frames in the video, and the
method further includes determining a corrosion level for a section of the
structure
by averaging the corrosion levels determined for each image of the series of
images.
The method preferably further comprises the step of generating a report
comprising information about corrosion levels of the structure. The report
will
generally include summaries of the corrosion levels found, including for
example
areas of greatest corrosion.
In a preferred embodiment once the corrosion level for an image has been
determined, the method further comprises the step of displaying an edited
image
of the area of interest. In the edited image the area of interest is coloured
according to the calculated corrosion level. For example, in the inspection of
offshore pipes, the pipe surface in the image may be shaded red to indicate a
high
corrosion level.
In order to allow the video, images and data to be reviewed and analysed
quickly
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and easily, in preferred embodiments the method further includes the step of
tagging the video to indicate points of interest while the video is being
captured.
Preferably the method further comprises a step of recording an audio message
while the video is being captured, to enable additional information to be
captured
to aid in the analysis stages.
Preferably the method further comprises transmitting said plurality of digital
images to a computer, and this will typically be achieved by transmitting the
continuous video to a computer.
In preferred embodiments of the invention the standard corrosion levels are
provided by reference images corresponding to each of the levels, and
preferably
the method comprises uploading a set of reference digital images to the
computer.
The set of reference digital images are analysed to determine a set of
reference
number averages, and preferably the step of analysing comprises selecting an
area of interest within said reference image, assigning a number value to each
pixel within the area of interest, the number value corresponding to the
colour of
that pixel, and calculating, from the number values of the pixels, a reference
number average for the reference image.
The invention further provides a method of analysing the corrosion levels on
the
external surfaces of pipes in an offshore installation, using a method
according to
the invention.
In these cases, once the digital video images have been captured offshore, the
method preferably includes transmitting the continuous video to an onshore
computer for analysis, in order to minimise the time spent offshore.
The invention further provides a camera system for use in the method according
to
the invention, the system comprising:
- a digital video camera for capturing digital video data;
- a memory, for storing said digital video data;
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- transmitting means, for transmitting said digital video data to a
computer;
and
- video marking means to enable a user of the system to place indicators at
specific places in the digital video during capture by the camera.
Preferably the system further comprises a pointer for aligning the camera so
that
the surface of the structure being analysed remains within a field of view of
the
camera. The pointer may be in the form of a light source which also acts to
illuminate the surface of the structure.
Preferably the camera is mounted on a piece of headgear to be worn by the
inspector or user of the camera system. This means that the images can be
captured hands free while the user moves around the structure. In other
embodiments the camera is fixed to a strap to be worn by the user of the
system,
for example over the shoulder of the user.
Preferably the video camera is a 3D video camera to aid in locating areas of
corrosion in relation to other parts of the structure.
In some cases it may also be advantageous for the system to further include
audio
recording means, to allow the user of the system to provide a commentary, at
least
during parts of the video.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described, by way of example only and with
reference to the accompanying drawings in which:
Figure 1 is a flowchart showing the method steps involved in capturing video
data
according to an embodiment of the present invention;
Figure 2 is a flowchart showing the method steps involved in establishing
reference data against which to analyse the captured video data, according to
an
embodiment of the present invention;
Figure 3 is a flowchart showing the method steps involved in assessing the
captured video data according to an embodiment of the present invention;
Figures 4a to 4c illustrate three areas of captured images comprising 64
pixels and
showing different levels of corrosion;
Figures 4d to 4f illustrate the number values assigned to each of the pixels
of the
three areas of Figures 4a to 4c;
Figure 4g shows the thresholding scale used to assign the number values in
Figures 4d to 4f;
Figure 5 illustrates a region of pipework that is being assessed using the
method
of the present invention; and
Figure 6 illustrates an output of an embodiment of the method of the present
invention, the output including a representation of the region of pipework of
Figure
5 including shaded or coloured sections indicating sections of greater
corrosion.
DETAILED DESCRIPTION
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The method of the present invention is used to determine the state of
corrosion or
surface coating breakdown of a structure or installation. In particular, and
as
described in the following example, this method may be used to examine
pipework
on an offshore installation such as an oil platform or in an onshore
installation such
as a refinery.
Due to the harsh environmental conditions, a regular maintenance program is
often needed to deal with corrosion or surface coating breakdown on the
external
surfaces of the pipes in these locations. This maintenance program may consist
of re-coating or re-painting the pipes or even replacing sections of pipe if
the
corrosion is particularly severe. In order to determine which sections of the
pipework require attention the method of the present invention allows the
extent of
the corrosion of the pipe to be accurately and objectively assessed and
compared
with reference corrosion limits typically used to monitor the maintenance
requirements.
Figures 1 to 3 show flowcharts illustrating the steps involved in analysing
the
corrosion state of a pipework structure according to the present method.
Briefly
the method comprises capturing image data of the structure of interest,
establishing reference corrosion levels from reference image data, and then
analysing the captured image data and comparing it to the reference data.
In the following description references to corrosion of a structure, for
example
pipework, includes both true corrosion such as rust as well as more general
surface coating breakdown or deterioration.
Figure 1 shows the steps involved in capturing image data of the pipework of
interest. In a first part of the method 10 an inspector, or user of the
method, uses
a digital video camera to record continuous images of the complete pipework
structure under investigation. The digital video camera is preferably a colour
digital camera having a resolution of 1080p and a frame rate of 25 frames per
second. In a preferred embodiment the camera has a fixed focal length,
however,
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in other embodiments the camera may be an auto-focussing camera, or may
include means to allow the inspector to manually focus the camera.
Continuous video data is captured in real time as the inspector walks around
the
area of interest. Because the location of pipework is often inaccessible and
exposed, in particular in offshore environments, it is preferable if the video
camera
is hands-free. For example the camera may be mounted on some form of
headgear such as a hard hat or headband, or the camera may be mounted on a
strap or piece of clothing worn by the inspector. It is desirable to mount the
camera in this way so that the inspector's hands are free to enable the
inspector to
move more safely around the installation.
Mounting the camera on a piece of headgear that is worn by the inspector has
the
additional advantage that the camera will point in approximately the same
direction
as the inspector is looking. As such, in order to record a complete video of
the
pipework the inspector simply walks around the installation looking at each
piece
of pipe included in the inspection. Preferably the inspector's line of sight
travels
along each pipe of interest so that the surface of the pipe falls within the
camera's
field of view.
To aid the inspector in this process the camera may include a laser pointer or
other suitable device to enable the inspector to know in which direction the
camera
is pointing. In embodiments including a laser pointer, the camera and pointer
are
aligned so that when the beam of the laser pointer falls on an object, that
object is
central within the field of view of the camera. In other embodiments, the
system
may include a monitor to allow the inspector to see the images that the camera
is
collecting, to ensure that the pipe surface of interest remains in the field
of view of
the camera, even if the pointer is not directed at the pipe.
If a laser pointer is used, it is desirable to include means to switch off the
pointer
during video capture. This prevents the laser light being captured by and
recorded
on the video, especially where the laser beam strikes an object of interest.
In this
respect, the laser pointer may be used in a first step 12 of the method at the
start
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of the inspection process to set up and align the camera system before video
capture is started 14.
In other embodiments the system may include light emitting means, for example
light emitting diodes (LEDs) that illuminate the field of view of the camera.
In this
way, the light source firstly acts as a pointer to allow the user of the
system to see
where the camera is pointing and secondly the light source provides even
illumination of the pipe's surface to enable improved analysis of the
resulting
images.
Alternatively or additionally some embodiments of the invention may include an
ultra violet light source. When using the system to inspect pipework, the
ultra
violet light may be combined with the use of fluorescent dyes applied to the
surface of the pipes to detect leaks in the pipework using a method known in
the
art.
The camera system may further include means for marking or 'tagging' the video
at particular time points. These means preferably allow the inspector to 'tag'
16
the video while it is being recorded in order to indicate a particular section
of
interest 18. These sections of interest may be related, for example, to a
change in
the type of pipe, a region of severe corrosion, or a region above or near to
an inlet
or outlet where corrosion conditions may change. The means for tagging the
video may be used to mark the video at each joint of the pipework to enable
the
resulting images to be divided during the subsequent analysis into different
sections of pipe that may be treated or replaced independently after the
inspection. In particular, the means for tagging the video may comprise a push
button that, when pressed, creates a time-coded event that relates to the
absolute
video reference. As such, the means for tagging the video at certain points
enables specific locations of interest to be found quickly and easily when
reviewing
the video footage.
The camera system may also include a microphone and audio recording means to
enable speech to be recorded 20 while the inspection is carried out and the
video
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is being recorded. The speech recording may be saved as part of the video, so
that the inspector provides an audio commentary during the inspection process,
or
alternatively audio recordings may be saved in separate audio files in a
memory of
the camera system. The video may then be tagged 22 to indicate the section of
the video corresponding to the particular audio recording.
The ability to record speech allows the inspector or user of the system to
record
information such as the names of the sections of pipe being inspected, the
deck
level on which the inspection is being carried out, or when the inspection
moves
from one module to another. The recordings may also be used to give additional
and/or more specific information about possible causes of increased corrosion
or
surface coating breakdown in certain areas, for example, the existence of
damaged module coverings that may have caused increased exposure in a
localised area.
The continuous video captured by the camera may be saved 24 to a memory
contained within the camera system or to an external or removable memory
device
such as a memory card. Preferably the camera system further comprises
transmitting means to enable the video data to be transmitted 26 to a
computer, on
which the analysis software is loaded. The computer may be located on the
offshore installation and accessed by the inspector, for example the computer
may
be a portable laptop computer used by the inspector, or the computer may be
located in an onshore location remote from the inspection site.
In some
embodiments, the camera system may be arranged to stream live video to the
computer to enable a second user of the system to monitor the progress of the
inspection. A means for tagging the video may additionally be located in the
computer such that, as the inspector walks around the installation, the second
user is able to tag the video to indicate points of interest. In systems not
including
a transmitting means, video data is uploaded to a computer from the memory of
the camera system once capturing is completed, ready for subsequent analysis.
The first step in the analysis of the video is to 'teach' the analysis
software the
corrosion levels of interest to the company for which the inspection is being
carried
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out. Each level corresponds to a different degree and extent of corrosion or
surface coating breakdown on the surface of the pipes. What maintenance, if
any,
is carried out, and on what timescale, for a particular section of pipe will
depend on
which corrosion level that particular section of pipe is categorised in.
Different
companies use different corrosion level categories, and even within a single
company the specific corrosion levels may vary between different sites, and
will
depend on factors such as the speed of corrosion, the material from which the
pipes are made, and the company's particular maintenance routine.
Figure 2 illustrates the steps followed to establish reference data
corresponding to
the corrosion levels. First, a set of digital images corresponding to the
different
levels of corrosion are uploaded into the analysis software 30. For each image
32
an area of interest in the image is selected 34. In this example the area or
object
of interest is the surface of a pipe. This is separated from the background of
the
image and any surrounding parts of the image, so that only the area of
interest is
included in the subsequent analysis. This separation step may be accomplished
using any known method, and may involve an edge detection program.
An area of interest selection step may not always be necessary, as the
reference
images may comprise only an area of the surface of a pipe, for example, in
which
case the whole area of the image is processed as described below.
Each pixel of the resulting area of interest or object image is given a number
value
corresponding to the colour of that pixel 38. Typically each image is
thresholded
36 so that each number value corresponds to a range of colours in the image.
For
each image the number values assigned to individual pixels are then averaged
40
over the whole of the image. This results in a number average value for that
image and correspondingly for that corrosion level. This process of
thresholding
and calculating a number average value is repeated 42 for each of the set of
digital images to produce a set of reference number average values
corresponding
to the corrosion levels. An example of a set of number average values for four
corrosion levels is shown in the table below:
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Table 1
Corrosion Level Number Average Value Number Average Range
1 1.3 1.55
2 1.8 1.56 ¨ 2.00
3 2.2 2.01 ¨ 2.40
4 2.6 2.41
For each corrosion level a number average range is then calculated 44. The
ranges are established by setting the number average value calculated for that
corrosion level as the median value of the range. The extent of the range is
then
determined by the difference between subsequent number average values so that
the ranges for each of the levels do not overlap. As such, for example, the
upper
value for the range for corrosion level 1 is 1.55 which lies halfway between
1.3 and
1.8, which are the number average values for corrosion levels 1 and 2
respectively.
Once the reference number average ranges for the corrosion levels have been
established, the captured video data can be analysed and compared with the
reference data to determine corrosion levels in different regions of the
pipework
structure under investigation.
Figure 3 shows the steps involved in analysing the data in a preferred
embodiment
of the method of the invention. At a first step the video is loaded into the
software
50 on a computer. The analytical software then saves 52 each selected frame of
the video as a separate image. It may be desirable to analyse every frame of
the
video, however, in most cases it is more practical to set the software to
select only
every fifth or every fiftieth frame as an image, for example. The number of
frames
selected and saved as images may depend on the length of pipe being analysed,
the frame rate of the video, or the available computing time and file space,
for
example.
For each saved image 54, corresponding to an individual frame of the video,
the
same analytical steps are then carried out. These steps will be described in
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relation to a single image (frame) but it will be understood that the same
process is
repeated for each of the saved images.
The image is first processed to separate the area or object of interest 56,
which in
this example is the surface of a section of pipe, from the background of the
image,
which may include other pipes in the installation or may be the surrounding
landscape. This object isolation step can be carried out by any method known
in
the art, and will not be described further here.
The next step is to threshold 58 the image so that a given number value is
assigned to a particular range of colours. The thresholding step allows the
different images to be compared directly by compensating for differences
between
each image, the differences including light level, shadow and angle of the
image
with respect to the surface of the object of interest.
Taking as an example the analysis of images of the surfaces of pipes, if the
surfaces of the pipes are painted a particular shade of blue, then the images
can
be thresholded so that the painted surface of a pipe in each of the images
falls
within a particular colour range, i.e. a particular range of shades of blue,
and is
therefore assigned the same number value, even if one image was taken in
direct
sunlight and therefore brighter, and another image was taken in shadow and
therefore darker.
Once the image has been thresholded 58, each pixel of the image is assigned 60
a number value corresponding to the colour of the pixel. This is shown for a
series
of examples in Figures 4a-4g. In this embodiment, pixels corresponding to the
colour of the paint are given low values and pixels corresponding to areas of
rust
or corrosion are given high values.
A number average value for the frame is then calculated 62 by adding together
the
number values of each pixel and dividing by the number of pixels in the image.
In
this example, the greater the number average value the more rust or corrosion
is
present in that image. The calculated number average value is compared 64 to
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the reference number average ranges calculated for each of the corrosion
levels
and a corrosion level is assigned 66 to this image.
A simplified example of three 'images' 70, 72, 74 is shown in Figures 4a to 4c
which represent surfaces having increasing amounts of corrosion, indicated by
the
darker pixels or squares. The thresholding scale 76 used to analyse these
images
70-74 is shown in Figure 4g, in which lighter pixels are assigned lower
numbers.
Figures 4d-4f show the results of assigning number values to each of the
pixels of
the images 70-74 based on this threshold scale 76. The number average value is
then calculated for each of the images 70-74 and compared to reference number
average ranges, for example those shown in Table 1. It can be seen that the
first
image 70, which has a number average value of 1.50 would be assigned to
corrosion level 1. The second image 72 (number average value = 1.75) would be
assigned to corrosion level 2, and the third image 74 (number average value =
2.14) would be assigned to corrosion level 3. In other embodiments this
assignment of values may be reversed so that areas of paint, or non-corroded
surface, are assigned high values and areas of rust or corrosion are assigned
low
values.
It may also be advantageous in some cases to record the number of pixels in an
image having a number value above a corrosion threshold value. This data could
be used to establish or assess the extent of the corrosion over the surface of
the
pipe, as a greater number of pixels having high values would suggest a larger
area
of rust or corrosion on the pipe. Furthermore, an image containing only a few
pixels having high values would indicate minimal or localised corrosion.
In addition, by using a system including means for marking or tagging the
video, it
is possible for the inspector (or user of the system) to additionally mark the
video
to indicate a small area of significant corrosion or surface breakdown
contained
within a larger area of satisfactory surface coating. This may be useful in
instances in which the area of corrosion is so localised or is of such a small
size
that the assigned corrosion level would be low, however the corrosion or
surface
coating breakdown is in a critical location in the structure.
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The corrosion level for each image is saved in relation to that frame of the
video.
By associating a series or range of frames with a particular section of the
pipe, an
average corrosion level for that pipe section can then be determined 68. The
frame numbers corresponding to discrete sections of pipe may be determined by
the inclusion of markers or tags inserted into the video by the inspector as
the data
was being collected, at the bends or joins in the pipe for example.
In some embodiments, rather than calculating an average corrosion level for a
given section of pipe, the highest corrosion level within that section may be
associated with the section so as to provide a 'worst case' picture of the
corrosion
levels of the pipework.
The software may be used to output 80 a report that summarises the extent of
corrosion over the pipework of interest. In particular, the report may list
the
different sections of the pipe that have different corrosion levels. The
report may
also highlight the particular regions of the pipe corresponding to the highest
corrosion level.
In some embodiments the report may include data in spreadsheet or tabular
format such that it is easily integrated with the operator's existing data.
For
example the data may be incorporated into the company's Risk Based Inspection
(RBI) system.
In a preferred embodiment of the invention, the corrosion level data is used
to
produce an edited video visually highlighting areas of the pipework having
severe
or extensive corrosion. In a particular example the edited video comprises
shaded
or coloured pipework, with each of the corrosion levels being associated with
a
particular colour. For example, corrosion level one may be blue, corrosion
level
two green, corrosion level three yellow and corrosion level four red. Once a
corrosion level has been assigned to an image, the image is then manipulated
or
edited so that the pipe surface in the image is coloured or shaded according
to the
assigned corrosion level and the colour edited image is then saved.
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This colour editing step is carried out for each of the selected frames in the
video,
and a second edited video is then generated using each of the colour edited
frames. In this way, when the edited video is played or viewed, a video of the
pipework is seen with the sections of pipes coloured corresponding to the
assessed corrosion level of that section. For example, Figure 5 is a schematic
diagram of a region of pipework that is being assessed and Figure 6 shows the
same region of pipework but this image has been edited so that regions of
higher
corrosion levels are shaded. This allows the locations and extent of the
corroded
sections of pipe to be visualised quickly and easily in relation to the rest
of the
pipework.
In a further embodiment of the present invention, the captured video data is a
three dimensional (3D) video. In this case, the resulting report generated
following
the assessment steps described above preferably includes a rotatable 3D image
highlighting the areas of the pipework in which corrosion has been detected.
The use of 3D images also allows depth measurements to be made which may be
used to enhance the corrosion assessment. The 3D views can be used to confirm
the location of particular areas of the pipework with respect to the
surrounding
structure and can give a clear indication of distances between neighbouring
pipes
or the geometries of bends and joins in the pipework for example. The
identification of the location of specific areas of pipework may be further
enhanced
by the addition of global positioning system (GPS) data and Gyro inputs. In
this
regard, it may be preferable if the system of the present invention further
comprises means for receiving GPS data.
The present invention, therefore, provides a method of assessing the surface
condition of a structure, and in particular surface corrosion on pipework in
harsh,
aggressive and corrosive environments such as offshore installations. By using
digital video capture and interpreting software to assess the captured data,
the
results are more objective in comparison to the more subjective interpretation
given by individual inspectors using prior art methods. The method of the
present
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invention allows a single standard of corrosion assessment to be applied
across
different inspection sites for example, even if different inspectors capture
the raw
video data. The software is also easily adapted to assess the data in relation
to
different corrosion standards in order to fulfil the inspection requirements
of
different companies.
A further advantage of the present system, especially in offshore locations,
is that
the video can be captured hands free thereby improving safety by keeping the
inspector's hands free to aid in negotiating his or her way around the
structure.
The method is also cost effective because by continuously recording a video
throughout the inspection, rather than needing to stop and capture specific
photographs at different locations, as well as record separately the location
at
which each photograph was taken, the data collection process is significantly
shortened and simplified.
In addition, in offshore applications there is a significant financial cost
associated
with sending an inspector offshore to collect the data. Therefore, by
simplifying
the data collection process through the use of video, the time for which an
inspector needs to be offshore is significantly reduced. Furthermore, all of
the
analysis can be completed onshore, including locating specific areas of
corrosion
within the network of pipes, because the use of continuous video data of the
entire
pipe network makes it easy to determine specific locations in relation to the
surrounding pipes and other structures.
Although the foregoing description has focussed on the use of the method of
the
present invention to analyse the corrosion and/or surface coating breakdown on
pipework in offshore environments, it will be obvious to a person skilled in
the art
that this method may be used in any situation in which there is a requirement
to
assess the surface condition of a structure or asset in relation to a set of
reference
conditions.
The method and system of the present invention, therefore, provides a
corrosion
CA 02830344 2013-09-16
WO 2012/127207 PCT/GB2012/050497
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assessment and analysis tool that overcomes the disadvantages of prior art
systems and methods.
