GEODETIC WORKS FOR THE SLOVAK GAS INDUSTRY
Jan HARDOS, Slovakia
Key words: surveying the lines and objects of
transition system, setting-out and surveying the pipeline defects,
measurement of displacement and settlement, mapping of local
distribution networks.
1. INTRODUCTION
The Slovak Gas Industry (further SGI) is a natural state monopoly
enterprise in the field of gas industry in Slovakia. It deals with
purchase, transit, distribution and sale of natural gas. It buys the
natural gas from Russia and assures its transit across the Slovak
territory to Czech Republic, Austria, Croatia, Slovenia, Italy,
Germany and France. The SGI is the second biggest gas transporter in
the world. The length of transit pipeline system makes 2 260 km in 4 -
5 lines (pipelines with diameter of 900 - 1400 mm). The SGI is
transporting 88 milliard m3 natural gas through its transit system per
year, whereas the domestic consumption represents about 7 milliard m3.
The distribution long-distance pipelines measure approximately 5
880 km and the local distribution network is about19 660 km long.
Together with the transit system it represents about 27 800 km gas
pipelines installed on the Slovak territory. About 1800 villages and
towns from the total number of 2878 are connected to the gas
distribution network, what means that about 81% population of Slovakia
has access to natural gas.
This huge system of underground pipelines, surface technological
objects (compressor stations, distribution nodes, transfer stations,
regulation stations etc.) including the operational and administrative
objects necessary for the purposes of design, construction, service,
maintenance and evidence of its equipment have always utilised the
geodetic activities.
Naturally, in the past that concerned mostly the analogue outputs
of geodetic works (paper maps) but since 1990 a gradual switch to
digital mapping technologies can be observed, which have enabled to
utilise the geodetic data actively via the modern information
technologies. The geodetic digital data connected to the state
co-ordinates system and to the state elevation system are of extreme
importance not only for the gas specialists but also for the
administrators of engineering networks, since a vast majority of
property administered by them (pipelines, cables etc.) is situated
under the ground and is invisible by naked eye. In this respect, the
geodetic activities, being performed in digital form, enable not only
to utilise the localized information in a more rational way, but they
mainly allow to eliminate or at least to reduce considerably the
collisions with other administrators of underground networks or other
users of the territory (design and construction of roads, railroads,
buildings etc.). That aspect then simultaneously increases the safety
of surrounding land from the economic and ecological viewpoint.
In my contribution I will try to outline briefly the main geodetic
activities performed for the transit system and also for the
distribution network of the SGI.
2. SURVEYING THE LINES OF TRANSITION SYSTEM
Since the start of construction of the lines of the transition gas
pipeline roughly in 70-ties of the past century, the individual lines
were geodetically surveyed in state positional co-ordinate system JTSK
(unified cadastre trigonometric network) and in the state level system
Bpv (the so-called Balt after adjustment). The pipelines were surveyed
partially in an open trench, but regarding the conditions of
construction site (fast burring of pipeline in the trench) they were
in most cases surveyed only after pipeline burial, i.e. the pipeline
axis was found by electromagnetic locators followed with measurement
at each about 100 m in the straight line or more frequently in the
curves. The surface equipment of gas pipeline (orientation poles,
connecting objects and outputs of cathodic protection) and other
underground equipment related to the pipeline (anode victims,
connecting cables, long-distance telemetric metallic cables, crossing
foreign engineering networks seen in the trench etc.) was measured
additionally. The results of surveying were plotted in analogue manner
to the state maps in 1 : 5000 scale, containing also the lists of
co-ordinates of the surveyed points. For the purposes of better
manipulation and archiving, the analogue maps and co-ordinate lists
were photographed on micro pictures.
Approximately since 1990, the digital mapping and processing is
employed. The analogue documentation of the line section was gradually
transferred to the CAD system MicroStation by the transfer from
co-ordinates or by digitalisation, in case when the co-ordinates have
not been preserved. A permanently stabilised position and elevation
point field was built along the pipeline with density about 500 m, to
allow its utilisation for additional surveying, updating and
maintenance of the lines.
Mapping then continued with a direct output to the CAD system
MicroStation by an additional surveying of all crossing subjects,
which passed or approached the pipeline axis within its protective
zone and which were not surveyed in the past during analogue mapping
due to the fact that the scale of the analogue map did not permit to
represent the details. In this way, all crossing communications, water
streams, railroads, above-ground conducts were surveyed for position
and elevation and also all foreign crossings of underground lines were
added by searching with electromagnetic locators, thus also those that
were not seen in the past, during the construction. The MicroStation
system and digital data have enabled their continual updating, mainly
as the foreign crossing lines are concerned, first of all by employing
the design co-ordinates of the foreign network and in the second stage
also by correcting the position and elevation from the geodetic survey
prior to burring in the trench.
Since 1993 the administrator of the lines of transition pipeline
started to utilise also the geodetic data also in the form of a simple
GIS on the basis of MicroStation and MDL applications. The directly
surveyed geodetic data were gradually supplemented also by other
digital information as for example:
- vectored map 1:50 000
- scanned map 1:10 000 a 1:5 000
- ortophotomap
- value map
- cadastre map
- scanned photographs of the lines and technological equipment
- technological schemes
That endeavour resulted on the end of 90-ties in an object-oriented
GIS, based upon the Intergraph (MGE, Geomedia) and ORACLE.
3. SURVEYING THE TECHNOLOGICAL OBJECTS
A part of geodetic works was also the mapping of technological
objects of the gas pipeline, as for example the compressor stations,
distribution nodes (Fig.1), transfer stations, line closures etc.
Fig.1: Measurement of technological objects
These objects are characterised with a high density of
technological equipment. Due that reason, the mapping also had a
specific character. Mapping was performed by a digital output to the
MicroStation system with subsequent printing of analogue maps in 1:200
scale. The position and elevation surveying of all above-ground and
underground pipelines was performed in JTSK and Bpv state co-ordinate
and level systems and were represented not by their axis but by their
actual diameter. All visible equipment (valves, spherical valves,
check outlets, flanges, pressure gauges etc.) were surveyed as well as
all above-ground and underground telemetric and power cables,and other
common objects of measurement (communications, buildings, fences
etc.). All pieces of equipment were supplemented by the description
(number and type of equipment, kind and type of cable etc.). Also the
object surroundings were measured up to the closest public approach
route. The resultant digital geodetic data (maps) were included into
GIS as well.
4. GEODETIC WORKS AT THE ANTICORROSION INSPECTION OF PIPELINES
Since all material is aged and deteriorated with the age and
external effects, the internal inspection of pipelines by use of the
so-called intelligent pig is an important part of the maintenance and
reconstruction works. The pig is an electronic device of cylindrical
shape, loaded into the pipeline though an entry chamber in the
compressor station or the object of distribution node and is carried
by the gas pressure in the pipeline over the distance of several tens
kilometres up to the nearest object with an exit chamber. This
equipment continually registers the passed distance and all
inhomogeneities of the pipeline as welds, corrosion, flanges, screens,
outlets, spherical valves, bends etc. These data serve for the repair
or replacement of the corroded or weakened parts of the pipeline. All
4 lines of the transit systems with pipeline diameter from 900 to 1400
mm in overall length 2260 km were inspected in that way. The passed
distance is then checked from outside by the so-called markers located
on the surface above the pipeline axis, what are in principle the
timed devices which are magnetically switched off after the pig
passage under the pipeline. The pig at the same time registers the
marker stationing. The distance passed in the pipeline is then
corrected by the registered time of pig passage, known spatial
distance between the markers and the known velocity of pig movement.
Each registered inhomogeneity in the pipeline can be thus exactly
positioned (as the distance from the initial point of inspection
stage).
4.1 Setting-out the pipeline defects
The main problem is that the accuracy of distance measured by the
pig is much lower that the possibilities of geodetic methods. The pig
does not move at a constant speed, since its velocity is besides the
gas pressure affected also by a rapid up- or down-slope of the
pipeline or by a local friction change in the pipeline etc. Thus, at
the passed distance of 10 km the error of pig can make several tens
metres but at the distance about 40 km this error may attain hundreds
metres. Finding the defect location on the pipeline surface would thus
be very inaccurate and would cause additional time and repair cost
losses. Therefore the markers were located on each 1.5 - 2 km above
the pipeline, surveyed geodetically and the exact space distance
between the markers along the pipeline was calculated and in this way,
the error in defect location on the pipeline was minimised. In spite
of reduced distance, the difference between the exact length of
geodetically determined curve and the length of curve determined by
the pig was from several cm to several metres. This problem of pig
inaccuracy would be eliminated, if all welds on the pipeline would be
geodetically surveyed always prior to its burial during its
construction in the past (the welds could serve as the natural markers
with exactly known co-ordinates).
4.2 Surveying the pipeline defects
After the setting-out, uncovering the pipeline and repair of the
found defect, the repaired point on the pipeline, new welds or old
visible ones that were not registered during the construction are
measured for the position and elevation above sea-level. The output of
such surveying is a graphical file in MicroStation system with a
protocol and the list of co-ordinates and elevations of the elements
surveyed on the pipeline. The pipeline administrator then includes the
new and corrected data into the GIS. In this way, also the old data on
the pipeline position and elevation that were in the past measured by
surface location with the aid of electromagnetic locators (with
pipeline depth also detected with the aid of those locators) have been
corrected.
5. TECHNICAL AND SAFETY MEASUREMENTS ON A TRANSIT SYSTEM
The transit gas pipeline system represents a certain potential risk
for its surrounding owing to very high gas pressures and therefore
some of its elements must be subjected to a regular safety monitoring.
This, besides the other aspects, involves a special geodetic
measurement of spatial stability of some technological equipment
situated on the surface. A significant static damage of the equipment
may result in the breakdown with catastrophic consequences on
ecological safety of the surroundings and may also cause considerable
losses due to interruption of gas transfer. Such equipment is for
example the air passages of large-diameter pipelines over the
waterways (Fig.2) and compressor stations.
Fig.2: Air passage of pipeline over the river
5.1 Measurement of displacement on the passages over the waterways
At construction of older lines of the transit gas pipeline, the
passages of pipelines over greater waterways were solved via air
passages with a supporting bridge structure (Fig.2) or sometimes - at
smaller width - also without any support structure. The up and down
displacement of pipeline, as the result of thermal expansivity does
not represent such a danger as the transverse or longitudinal
displacements of the concrete, the so-called braking blocks, which may
impair the strength of pipeline welds. By the specialists, the
waterways in general pose a certain risk of reciprocal displacement of
their banks at the seismic activities (seismic shear). The newer
pipelines have been solved by the inverted siphon under the river
beds.
For the purposes of monitoring the displacements of concrete
braking blocks, support bridge structure and the pipeline itself, a
permanently stabilised local network of 6 reference points (with 3
points on each side of the pipeline) have been built on the protective
dams of the river in proximity of each air passage. These points are
positionally determined with the accuracy below 1 mm (by a precise
multiplied angular and lenght measurement with a depended centering
using precise total stations) with subsequent adjustment. Since the
displacement of these points cannot be totally excluded, the network
is always assessed as a dynamic one, with stability assessment of
individual network points based upon the mathematical and statistical
methods. Regarding the elevation, the network is again determined at
each measurement stage by a very precise levelling from the distant
levelling points with the accuracy up to 0.5 mm. After stability
measurement of the reference points, the permanently stabilised points
on the pipeline, support bridge structure and concrete braking blocks
are measured by the method of spatial intersection from the horizontal
and elevation angles. In this manner 20-28 points are surveyed on each
air passage from two combinations for the horizontal angles and from 3
combinations for the elevation angles. Regarding the fact that the
length of sight lines ranges from 50 - 100 m, the mean error of
determination of X, Y, Z co-ordinates does not exceed 1 - 2 mm. The
result of measurement is the table of spatial displacements of
observed points with an appropriate graphical representation of the
displacements in vertical, longitudinal and transverse directions
related to the pipeline.
5.2 Measurement of settlement of turbocompressors
The compressor stations of transit gas pipeline assure the
necessary gas pressure in a transit system for the purposes of gas
transfer in the 4-5 lines for long distances. Four compressor stations
on Slovak territory are spaced by about 100 km from each other. They
represent an extensive and complex technological system with automated
processes. 21 to 23 turbo machines (gas turbines with single stage
compressors) with the installed power of 6 MW for each turbine were
employed. The stability of foundations of the individual technological
components, which are mutually interconnected by a network of
large-diameter pipelines under very high pressure (up to 7 MPa) is
extremely essential from the viewpoint of safety and service
continuance. It is important that the individual foundations should
not decline or settle unequally, what might impair the turbine running
or the strength of welds in the pipeline.
For the mentioned reasons, the elevation settlement of the
foundations of turbocompressors, outlet spherical valves and the
concrete foundations of pipeline supports is regularly monitored
geodetically twice in a year. Up to 300 check point marks in five
halls are stabilised in one compressor station (1 hall for 1 line with
about 60 check point - Fig.3). These points are measured by a system
of levelling traverses by the method of precise levelling with the
mean error below 0.25 mm. To assure this accuracy at very unfavourable
conditions for measurement (great thermal difference inside and
outside the halls, high noise level - attaining 100 dB, vibrations),
the system of levelling traverses is adjusted at each measurement
stage by the least squares method - conditional adjustment. For a long
period of measurements, the irregularity of settlement between the
technologically related foundations did not exceed the value in order
of 3 mm.
Fig.3: Schema of levelling traverses in Hall 1 on
Compressor station IV
Fig.4: Graph of settlement of spherical valves
6. GEODETIC WORKS FOR THE LOCAL DISTRIBUTION NETWORKS
Majority of geodetic works is being performed for the local
distribution networks in the villages and town, i. e. from the
regulation stations of natural gas on the village borders thorough the
main distribution systems in the village up to the individual
connections to the houses (users) terminated with the main house
closing valves. Approximately since 1990 the geodetic surveying of the
local networks was processed first on the Autocad CAD system, later
jointly on the MicroStation system, based upon the SGI guidelines. „Creation
and processing of the geodetic and digital map documentation of local
networks„. These guidelines assure a unified geodetic surveying and
processing of the local gas pipeline networks on the territory of
whole Slovak republic. The guidelines specify a unified way of digital
processing of map contents with an exact structure and content of
individual reference files of the MicroStation system. That enables
the administrators to facilitate an easier data transfer to GIS SGI.
The mapping is done in a unique 1:500 scale in the JTSK state
positional system and in the Bpv state elevation system.
The local networks are mostly surveyed during the construction of
new networks, but also the existing old networks, which were not
mapped digitally in the past are added gradually.
The geodetic works for the new-built local networks can be divided
into two main time stages:
In the 1.stage, the planimetric component of a map and altimetry of
the surroundings of the future gas pipeline are surveyed (unless there
exists a previously surveyed suitable digital document) - the
so-called street bands, namely the street in its whole width up to the
front line of the buildings or in an approximate band width of 30 m.
All common objects are also surveyed (houses, fences,
communications, trees, lamp posts, bridges, ditches, slopes, external
signs of all underground engineering networks, routes of all conducts
above the ground etc.). The digital planimetric component of a map and
altimetry surveyed in such a way are then provided to designers to
design (to project) the local gas pipeline network.
In the 2. stage, after start of construction the surveyor surveys
all new-built gas pipelines (steel or plastic ones) in an open trench.
Surveyed are also all points of deviation of the line (horizontal and
vertical deviations) on the gas pipelines, at straight sections in max
distance up to 40 m, points of change in diameter and material of the
pipeline, points of branch attachment, main closing valves of house
connections, other devices of gas pipelines as the drain valves, air
release valves, by-passes with their accessories, all foreign
engineering networks crossing the pipeline route in the trench,
interconnecting objects, stations of cathodic protection with their
devices, orientation poles etc.- (Fig. 7). In the recent years also
topology of measured elements (line, point, area) has been maintained
with their links, to facilitate the loading of measured data into an
object-oriented GIS.
The geodetic works performed for the old existing local networks
are actually the same as those done for the new-built networks with
the only difference that the measurement of street bands is joined to
one time stage together with surveying the pipelines which are,
however, set out by the electromagnetic locators either by the
employees of gas enterprise or directly by the surveyors, as long as
they master that operation and have the appropriate equipment.
Typical feature of digital maps for the local gas pipelines is,
that all deviation points of underground gas distribution are in the
final stage computer dimensioned from the nearest visible measurement
subjects (houses, fences, poles, shafts etc.). These dimensions serve
for the maintenance specialists of the gas pipeline to locate easier
the gas pipeline networks in the terrain, since for the site purposes
these specialists are using the analogue (paper) prints of digital
maps.
A part of geodetic works for the distribution gas pipeline networks
is naturally also the surveying of long-distance, high-pressure
pipelines of different levels, from tapping on the transit system or
on underground storage tanks to the connection gas pipelines between
the villages, surveying the regulation stations, other gas objects
etc.
7. CONCLUSIONS
The Slovak Gas Industry belongs to the greatest contractors of
geodetic works in Slovakia, together with the telecommunications,
owing to great boom in gas introduction for the past 10 - 15 years. A
great number of smaller and bigger private geodetic companies have
participated in all those works. At present, such works are on decline
with respect to gradual completion of gas introduction process on a
large part of the territory of Slovakia.
It may be finally concluded, that these works done for the SGI have
brought about a considerable merit, owing to a rapid technological
modernisation and development of the Slovak geodetic companies, which
are today employing the most advanced measuring, computing and image
processing technology, starting with the total stations and GPS to
AutoCad 2000, MicroStation under the Windows NT, Geomedia etc.
BIOGRAPHICAL NOTE
Jan Hardos
Education: (1970-1975) Slovak Technical University in
Bratislava, Faculty of Civil Engineering, specialisation: geodesy and
cartography. He attained the certificate of authorised surveyor for
engineering geodesy in 1980 and for cadastre in 1992.
Professional experience: Since 1975 he performed and managed
the surveying works mainly in engineering geodesy (investment
construction, deformation measurement, mapping operations). In years
1985 - 1989 he acted as a Czechoslovak expert for the Ministry of
Water Economy of Algeria at geodetic assurance of construction of 4
dams in North-East Algeria. Since 1993 he is the Director and joint
owner of a private geodetic company SIGEO Ltd Bratislava.
Membership in professional organisations: (1990-1995) the
member of chair of Slovak Union of Surveyors, since 1996 a member of
the Directive Board of Chamber of Surveyors and Cartographers.
Vice-president of Slovak National Committee for FIG and national
delegate for the 6. Commission of FIG since 1998, national delegate
for CLGE (Council of European Geodetic Surveyors) since 1999.
CONTACT
Dipl.Ing. Jan Hardos
SIGEO s.r.o.
Racianska 71
832 59 Bratislava
SLOVAKIA
Tel & fax + 421 7 4445 8342
Email: sigeo@netax.sk
15 April 2001
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