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INFRASTRUCTURE HEALTH MONITORING |
Monitoring traffic loads and condition of bridgesTo be able to assess a bridge’s condition and remaining safe service life, the status of the integrity of the structure is crucial information. Residual service life can be estimated more accurately by the combination of data for actual traffic loads and accurate condition data from critical points combined with predictive modelling of the whole structure. Early detection of deterioration of the structure may reduce operational costs as any required maintenance can be planned in due time and optimized with respect to the schedule for repair. The patented FEMM (Ferrx ElectroMagnetic Method) is well suited for such applications with its unique monitoring features. FEMM measures directly the stress response in the steel structure caused by the traffic loads, and also the stress due to any resonance vibration. Furthermore, it monitors the effect these stresses have on the monitored steel, e.g. changes of residual stresses in welds and material degradation as well as crack initiation and growth. |
Girder bridge |
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This girder bridge is more than 60 years old. FEMM sensors are retrofitted on the lower and upper flanges of the girder to monitor traffic loads. The bridge will in periods be used for the European route E6 traffic with a high number of heavy vehicles that may exceed the bridge classification. Therefore the traffic is monitored. Data is transmitted to Ferrx daily and provides for near realtime monitoring. This installation is also part of an R&D project where SINTEF Ocean has made a digital model of the bridge which, when integrating with the FEMM system, makes a digital twin of the bridge. The project is financially supported by Trøndelag’s regional research fund (RFF Trøndelag) which has been decisive for running the project. |
Framework bridge |
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This framework bridge is more than 80 years old. Four FEMM sensors are installed on different truss elements for monitoring different types of stress. The traffic is heavy and the stress is measured for monitoring the highest vehicle load in a period, and also stresses caused by 10Hz resonance vibration. The picture above right shows one of the sensors. |
Railway rail stress monitoring |
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OIL AND GAS APPLICATIONS |
Non-intrusive pipe monitoring |
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Fatigue monitoring of subsea riser |
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FEMM MONITORING CAPABILITIES |
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The FEMM method and technology was certified in 2016 by DNV in accordance with DNV-RP-A203. A FEMM system is used for monitoring all the different parameters just by selecting appropriate location and configuration of sensors and processing data with the dedicated algorithms to get the best results. |
Stress monitoringStress measurements in ferromagnetic steel are relative to a previous measurement. Calibration curves for elastic stress can be established based on measurements at known loads, either on the actual structure or on specimen of the same type of steel. Different types of stress can be monitored: elastic stress, residual stress changes and maximal stress between two measurements. Changes of stress beyond yield make permanent changes in the steel material and is detected. |
Fatigue monitoringThe material changes in ferromagnetic steel during a fatigue process are measured by FEMM long before cracks are visible. The Fatigue process refers to the irreversible changes in a material or component that is exposed to cyclic loading. These changes in steel are microstructural changes before the onset of macroscopic crack growth. Changes in microstructure are closely related to changes in the density and structure of dislocations. The fatigue process is commonly divided into three stages:
The measured response changes according to the degree of changes in the steel impedance parameters, e.g. when dislocation density increases and later micro-crack density increases and grows to more continuous cracks, the response signals change accordingly. By analyzing the response signal, changes of magnetic permeability and electric resistance are estimated, and based on these parameters the degree of material degradation can be characterized in due time before any crack is visible. Based on many fatigue tests with different welded structures a response pattern has in agreement with theoretical material changes been verified and is used to predict fatigue development. |
Crack detection and monitoringThe sensor matrix is located to cover the area where cracks are expected, most likely a weld, and it will be detected whether the crack starts in the outside surface or inner surface of a pipe or even inside the weld or HAZ area. The matrix sensing (sensor) direction is oriented perpendicular to the expected crack direction. If this direction is not known, a matrix sensing in both directions can be installed. |
Corrosion monitoringCorrosion internal in pipelines is more or less uneven and the degree of corrosion attack can vary around the pipe’s circumference e.g. be more severe in the bottom section. This makes it advantageous to monitor a continuous area of the pipe to be able to get a representative picture of the distribution. In general, the location expected to be most exposed to corrosion is selected for installation of the sensors. Based on the expected type and location of corrosion, e.g. localized attacks in the bottom section of a pipe, a sensing matrix is designed for best sensitivity and coverage. The whole area covered by the sensing matrix is monitored for any internal metal loss. Initially, a measurement is taken at known wall thicknesses and stored and used as a reference for the following measurements, which give the change due to corrosion attacks. When localized metal loss is detected, the actual depth of e.g. a pit can be estimated using the patented FEMM algorithm based on the transient potential drop signal. |
Erosion monitoringErosion internal in pipes is usually localized metal loss that most frequently occurs in bends and tends to be most severe in the outer radius of the bends, however, due to turbulence also at other locations in the bend. The shape of the erosion varies related to the pipe geometry and internal flow. Both carbon steel and duplex steel can be monitored. The sensor matrix is designed for optimized sensitivity based on the expected shape of the eroded area. For example, if the erosion is widespread and in the outer radius of a bend, the matrix is distributed along the outer radius. If the erosion is expected to be a narrow groove along the outer radius of the bend the matrix can be along the pipe’s circumference which will significantly improve sensitivity. Also, a combination of these matrices can be applied in case the shape of the erosion is difficult to predict. Sufficient area is covered to be sure to pick up the most severe attacks. Each Sensor Interface SI has four different sensor matrices which can be located to monitor four separate erosion locations. When metal loss is detected, the actual depth of the deepest attack within a matrix can be estimated. |
INSTRUMENTATION |
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Example of installation for monitoring of four different areas for stress and cracks in a bridge coverplate. One system with eight SI’s can monitor 32 locations within approx. 20m. The above system is an autonomous standalone online system with several options for data transfer to the user. A FEMM system consists of four main modules:
This modularity provides for extensive flexibility to optimize the system configuration and performance for the different applications. The system design based on many years of relevant field experience has also been optimized with respect to reliability and ease of installation, e.g. there is no steel reference needed, which significantly simplifies the preparation and installation on the steel structures. Sensors and all fixed installed components shall have the same operational lifetime as the monitored structures. The sensor interface is designed for at least 25 years of operation. The sensor and sensor interface design provides for redundancy and improved reliability. One system comprising one instrument and up to eight sensor interfaces can e.g. monitor one to eight nearby pipes or on a structure up to 32 locations within 20m from the data acquisition unit. |
Instrumentation modules |
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About Ferrx and FEMMFerrx is an independent company located in Trondheim, Norway with the business idea to provide the FEMM technology for different onshore and offshore markets. Ferrx patented the method called FEMM (Ferrx ElectroMagnetic Method), and with support from several oil companies and Innovation Norway and The Research Council of Norway developed and industrialized the technology. A system for monitoring fatigue in steel risers has been certified by DNV This technology measures directly the actual response and condition of steel structures in selected locations and thus makes possible in a simple way more accurate estimates of the condition of the whole structure and the safe operational life. ResourcesWe appreciate the importance of having a team of highly qualified and motivated employees. We offer interesting opportunities within advanced methods and technology in close cooperation with clients. The employees will receive competitive compensation and be invited to share in the values they create as team members at Ferrx. Contact usFerrx as Brøsetvn 168 N-7069 Trondheim Phone no: +47-40001595 info@ferrx.no |
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