On-line monitoring
of reconstruction DN500
Goleniów-Police gas pipeline.
Dr inż. Wiesław Bereza, mgr inż. Sebastian Kowalik
Gas Pipeline Monitoring | Poland
Applications
Location: Olszanka, Poland
Site monitored since: 2021
Consultants : Wiesław Bereza, Sebastian Kowalik
overall tasks
Reconstruction of the DN500 Goleniów-Police gas pipeline (stage I) in the area of the Olszanka and Roztoka Odrzańska nature reserves requires the construction of a new gas pipeline line in the form of a directional drilling beneath the riverbed and the subsequent connection to the existing line. For this reason, the uncovering of the existing gas pipeline situated in complex ground conditions was required. In order to avoid failure or gas pipeline damage the construction contractor introduced structural monitoring of the behavior of the uncovered sections of the existing gas pipeline.
Online monitoring of the works allowed the possibility not only to report details about the existing structural deformaties of the gas pipeline pipe, but also it was able to gather data in the event of a critical situation requiring immediate response or the suspension of construction works. A simultaneous analysis of the finite element method made it possible to determine the structural integrity of the steel pipe used in the gas pipeline at each stage of works and the indication of alarm thresholds to signal any threat to the pipework of the gas pipeline operating in a continuous mode (without stopping the gas flow).
Existing gas pipeline and its location
The Goleniów-Police gas pipeline is a high-pressure gas pipeline DN500. It is a tread providing gas supply to, e.g. the city of Szczecin and the chemical plant in Police. The operator of transmission gas pipelines of natural gas is GAZ-SYSTEM company. This pipeline has been designated to undergo reconstruction. The purpose of the project was improvement of the technical conditions of gas transmission by substituting the depleted gas pipeline (dating back to 1982) with a new thread DN500 MOP 8.4 MPa. Approval for the reconstruction of the DN500 Goleniów-Police gas pipeline (stage I) in the area of the Olszanka Reserve and Roztoka Odrzańska was granted on the grounds of the Act on investments regarding the liquefied natural gas regasification terminal in Świnoujście. Greater depth of the gas pipeline underneath of Roztoka Odrzańska and disassembling the existing two lines of the DN500/DN400 gas pipeline enabled the realisation of another crucial investment - deepening the track of the Świnoujście-Szczecin watercourse to a depth of 12.5 meters. Nevertheless, it should be noted that this is an area partially protected by the Natura 2000 Programme, which determines a network of protected natural areas such as the Olszanka Reserve and Roztoka Odrzańska.
PHOTO 2. Roztoka Odrzańska
The Olszanka Reserve is a forest and peat area in the western part of the Goleniowska Forest. The purpose of this reserve is to protect and preserve areas of the Baltic berk, alder forests and bog forests with numerous places containing rare and endangered plant species. The reserve, along with its immediate surroundings, is the habitat of the white-tailed eagle. In turn, Roztoka Odrzańska is part of the bay of the Szczecinski lagoon in its southern part. Roztoka waters are shallow, their average depth is about 1.3 m, the pool is 10 km long and about 6 km wide. The Odra river flows in to it. the Szczecin-Świnoujście shipping runs through the middle of Roztoka.
The Świnoujście-Szczecin fairway is a man made channel approximately 68 km long. It leads from the Pomeranian Bay through Świna in Świnoujście to the seaport in Szczecin. This water course was created in the seventeenth century. The width of the water course, where traffic control takes place, is about 250 m and its depth is 9.5 m. It is currently being deepened in order to accommodate larger units. One of the main obstacles of this enterprise was the shallow location of the gas pipeline and the threat of its possible damage.
PHOTO 3. Świnoujście-Szczecin fairway in the area under construction investment.
The scope and technology of the investment
The described scope of the investment concerned the crossing of Roztoka Odrzańska/ Odrzańska Rostock using the underground passage method and the dismantling of two lines of the old gas pipeline DN500 and DN400. In the waterfront zone, it is planned to connect to the existing system situated on the western side as an underground facility, whereas sheltered with a secondary embankment on the eastern side. Crossing Roztoka Odrzańska was carried out in the form of HDD controlled drilling in the Intersect technology. The length of the drilling is 1814 m. It is the first drilling of such kind in Poland. Works involving this method consisted in drilling a hole at the same time from the opposite banks of the river in two directions.
Horizontal directional drilling (HDD) is a modern technology consisting in performing horizontal directional drilling. It belongs to the group of so-called trenchless technologies. Horizontal drilling is a type of directional holes. Due to the use of modern measurement and control systems as, the course of the drilling and the location of the starting and ending points coincide with the aim of the design. This solution can be implemented in heavily armed and urbanized areas. In the case of Roztoka Odrzańska, it has been proven that this solution is also well suited to environmentally protected areas. The essential part of the installation performed using the technology of horizontal directional drilling is a casing pipe inside which the cable is pulled or the pumped medium flows (photo 4).
PHOTO 4. Scheme of horizontal directional drilling (according to Solid-Drill).
Drilling and extracting the gas pipeline for the reconstruction of the Goleniów-Police DN gas pipeline (stage I) in the area of the Olszanka reserve and Roztoki Odrzańska was performed from September to November 2020. Works were carried out simultaneously from both banks at a rapid pace (24 h / 7 days a week) regardless of weather conditions, due to which possible delays were avoided.
Including a borehole into an existing line
After crossing Roztoka Odrzańska, completed in the form of a HDD controlled drilling in the Intersect technology, the contractor had to encounter another difficult stage - connecting the drilling to the remaining onshore line of the gas pipeline. The project presumed connecting the planned gas pipeline with the existing one through the application hermetic method (without stopping the gas flow).
PHOTO 5. The stage of extracting the gas pipeline.
There are different location, ground and water conditions on both sides of Roztoka, where it was necessary to join the existing lines of the DN500 gas pipeline. On the west side we had to deal with an underground gas pipeline lying in a layer of Baltic peat flooded with groundwater. In the eastern part of the brook, the gas pipeline was lying on the surface (covered with earth embankment), in the sandy ground and without the interference of groundwater. Recognition of water and ground conditions by preparing both geological-engineering and hydrogeological documentation made within construction design, made it possible to reliably forecast the working conditions of the gas pipeline on both sides of the lagoon. The existing gas pipeline DN400 and DN500 analyzed, located on the western side of the rostock (in the layer of the Baltic peat berk), had to be exposed what forced the need to lower it high groundwater level. This created unfavorable working conditions related to the formation of the connection. The risk of a prolonged lowering of the groundwater level could lead to uncontrolled peat collapse. According to prof. Jan Jeż, this is an irreversible geological phenomenon. A gas pipeline placed in such conditions may be subjected to enforced displacement and consequently, be unsealed due to deformation of the transmission pipe. In order to perform the construction works, the excavation zone had to be drained by using a system of well point filters which lowered the groundwater level in the peat. This solution was agreed upon only under the condition of constant observation of the displacements and deformations of the gas pipeline pipe. This monitoring was due to inform about the possibility of exceeding the limit values, resulting both from the change in the way of working (beam element) and the sensitivity of the ground resulting from the changes in ground parameters in the farther side - outside the excavation area.
PHOTO 6. An uncovered fragment of the existing gas pipeline in the western shore.
PHOTO 7. An uncovered fragment of the existing gas pipeline on the eastern side shore.
On the eastern side of the lagoon, ground conditions – according to prior diagnosis - were much more stable. However, it turned out that the rigid mounting of the gas pipeline in the remaining layer of secondary sand embankment is not at all favorable for work of the gas pipeline pipe which functions as a beam and is subjected to high internal pressure. Admissible stresses margin, which could have occurred from the beam work system, was insignificant.
Construction monitoring system
For structural monitoring of exposed fragments threads of the existing gas pipeline, the operating conditions of which were to be changed, geometric models of these sections were built along with a part of the adjoining ground. This was to allow constant analysis using the numerical finite element method of the work of these elements and verifying the generated values of stresses and deformations. Taking into account the adjoining fragments of the subsoil was to model conditions as closely resemebling reality as possible. The actual measurement of the behavior of the gas pipeline was controlled by a system of bi-directional inclinometers working in online mode (on an ongoing basis, with the frequency of measurements every 5 s). Photo. 8 shows the excavation model for the western side (grey colour marks peat leyers) and for the eastern side (yellow colour marks the sand).
PHOTO 8. Calculation models of gas pipeline fragments on the western and eastern banks.
A BeanAir wireless two-axis inclinometer sensor system was used to measure the behavior of a gas pipeline pipe with a measuring range of ± 15°. The measuring accuracy of the inclinometer sensors is at least ±0.005° with the declared measurement resolution of 0.001°. The measuring repeatability ±0.003° on full Scale for ±15° version. This is high accuracy. Additionally, these sensors are dust and water resistant in the range of IP67, which allows even short-term flooding with water up to the depth of 1 m. The use of sensors resistant to dust and water in the scope of IP67 was particularly important for the area of the Olszanka reserve (western part), where despite of the lowering of water level there was still posing a real threat to the sensors. The mud did not create conditions conducive to the functioning of the equipment as well.
PHOTO 9. Photo of BeanAir inclinometers.
The system of sensors was connected with computers registering the measurement data and modems to communicate via the Internet with the supervising (external) system unit. System built in such a way, repeatedly used by the authors has proven itself in the field during monitoring cubature and linear objects. Measurement values saved in a two ways, in the sensors’ memory and in space (cloud), could be redirected for further processing and analysis. The Internet of Things system allowed for automatic filtering of noise and measurement anomalies that could introduce unnecessary confusion and ambiguities in the result interpretation. It created favorable conditions for collecting data, analyzing it and then processing it into specific useful information.
Studying of the behavior of the gas pipeline, realized through the construction monitoring system, required a stable mounting of measuring sensors to the surface of the transfer pipe. On the other hand, the operator did not agree to any mechanical fixing of the elements or, at a later stage, to leave the fragments glued or welded. Therefore, the inclinometers were installed to the gas pipeline pipe by using strong neodymium magnets. This solution was previously verified experimentally. It has been tested whether the magnets, attached in close proximity, will not interfere with the functioning of measuring devices. The application of the magnets required only cleansing the surface of the gas pipeline from dirt and removing local anti-corrosion and anti-water insulation layer.
PHOTO 10. Mounted inclinometers in part of the exposed gas pipeline on the eastern bank.
Inclinometer sensors allow to control the inclination of the device from the vertical. Depending on the type, they can measure in one or two directions. However, it is always a deviation from a vertical line treated as an absolute or relative value. Thanks to the use of horizontal pads in the described case, each sensor could be fully used and simultaneously measured the tilt in two planes. Therefore the use of four sensors on the uncovered part of the pipe actually allowed to control the behavior of the element by measuring eight inclination values (four in each support section).
FEM analysis
On the basis of the material assumptions and the assumptions of the functioning of the gas pipeline pipe, a numerical analysis using the finite element method of a three-dimensional element has been performed. It allowed to take into account all foreseeable operating conditions of this element as well as environmental impacts. Additionally, the element model could be used to illustrate the behavior of the gas pipeline basing on continuous measuring of displacements and strains. The design conditions for the gas pipeline were adopted in accordance with the guidelines included in the construction project. Such an analysis allowed to determine the state of effort of the transmission pipe loaded only with internal pressure according to PN-EN 1594:2014-02 and in later working conditions. The value of the design factor for the 1st class of gas pipeline location was adopted according to RMG (Journal of Laws 2013.06.04, item 604).
A significant elemet of further analysis was the behavior of the element, taking into account the parameters of the subsoil in the support zone for both output values (according to geotechnical research), as well as in the event of a lowering of the water level ground. The gas pipeline then began to work as an element interrupting the depression cone generated by the use of well points. The graphs (Photo 11) show the change in behavior of the gas pipeline which was initially loaded only with its own weight, and then with its own weight under changing ground conditions.
PHOTO 11.
An additional anomaly in the work of the pipe element was the appearance of eccentric moment caused by the attachment of the cap weighing up to about 30 kN and generating a torque due to putting an additional pipe on it. The situation was complicated additionally, by fixing medium-compact sand in the substrate, generating high friction of the soil against the twisted gas pipeline pipe (photo 12).
PHOTO 12.
On the one hand, this behavior was predicted numerically by analyzing the 3D model, and on the other - controlled and compared with the initial forecasts on the basis of current monitoring results. This approach made it possible to determine the acceptable limit values for the maximum displacements (deflections and rotation) of the gas pipeline pipe in exposed excavations, as well as to control their values in reality. These values were divided into threshold values (I threshold alert) and critical values, which may lead to unsealing of the gas pipeline (II threshold alert). The presentation of such values made it possible to ensure continuous operation without the need for successive control and observation of the functioning of the gas pipeline.
Threshold values:
Inclination angle of the pipe at a distance of 3.5 m from the center of the span: 0.1834° for the western shore,
Curving angle of the pipe at a distance of 3.5 m from the center of the span: 0.164° for the eastern shore,
which corresponds with the values:
maximum deflections (in the middle of the span) for the western bank use max = 16.58mm,
maximum deflections (in the middle of the span) for the east bank use max = 10.73 mm.
When applying the collar:
pipe torsion angle at a distance of 3.5 m from the span center: 0.98° for west bank,
pipe torsion angle at a distance of 3.5 m from the span center: 0.38° for east bank
The determined calculated critical values (for deformations of the gas pipeline) significantly resulted from the carrying capacity of the transmission pipe and the changing parameters of the substrate ground. These parameters may have changed during the analysis. Sample results of the shape of the pipe geometry (deviation from the original location in two directions) at selected measurement points are presented in the charts (Photo 13) on the timeline. Intermediate stages are related to the execution period of the excavation, drainage, loading connections, and finally, with backfilling the excavation.
PHOTO 13. Graphs of the geometrical behavior of the gas pipeline pipe on the timeline.
Constructional monitoring of the operation of the high pressure gas pipeline DN500 Goleniów-Police in the area of the Olszanka reserve and Roztoka Odrzańska allowed to control the behavior in real time, deformations and displacements of the object during the construction works. Monitoring, preceded by a proper numerical analysis using the finite element method, allowed not only to observe the behavior of the gas pipeline, but also to control security status. This is especially important in the case of a component that is sensitive to excessive stresses that can lead to pipe unsealing - such as a high-pressure gas pipeline.
The proposed system of 8-way monitoring combined into a uniform system gives a full picture of the behavior of a separated section of the gas pipeline. FEM analysis is necessary to determine limits that may be allowed in specific working conditions and changed parameters of external influences. Only the combination of these two operations gives a clear picture of the condition the gas pipeline is in when it’s subjected to unusual actions.
Authors: Dr inż. Wiesław Bereza, mgr inż. Sebastian Kowalik
Website: www.risscontrol.com