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INFRASTRUCTURE 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 and crack initiation and growth. |
Girder bridge |
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Framework bridge |
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OIL & GAS APPLICATIONS |
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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 were certified in 2016 by DNV GL in accordance with DNV-RP-A203. An FEMM system is used for monitoring all the different parameters just by selecting appropriate location and configuration of sensors to get the best results. The general monitoring capabilities can be summarized as follows:
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Stress monitoringStress measurements in ferromagnetic steel are relative to a previous measurement, preferably taken with known stress or load level with sensor installed on location, or measurements on specimen with same type of steel. Calibration curves can be established based on two known loads and stress levels and quantification of measured stress level is thus possible. The steel ″remembers″ previous external loads, i.e. the load has changed the magnetization of the steel. This is measured by FEMM and is called remanent stress, which shows the highest stress since the last measurement. This magnetization is wiped out by the new measurement, and the permanent change can then be measured, e.g. permanent stress during the measurement. Plasticity, permanent changes in the material caused by stress exceeding yield, is detected. This is, for example, observed when monitoring areas when residual stress changes due to external loads. Changes of residual stresses related to welds are measured with sensitivity also for changes in depth location. |
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. When the monitoring records a significant crack, the maximum depth can be estimated. Thereafter the crack growth is monitored and reported |
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 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 |
SYSTEM CONCEPT |
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Example of installation for monitoring of four different areas for stress and cracks in bridge cover plate. One system with eight SIs 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 non-retrievable 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 now called FEMM (Ferrx ElectroMagnetic Method), and with support from several oil companies and Innovation Norway and The Research Council of Norway developed and industrialized systems for the O&G market. A system for monitoring fatigue in steel risers has been certified by DNV GL. The FEMM technology is well suited for long term unattended autonomous monitoring of remote locations e.g. subsea or buried pipelines, or in harsh environment, e.g. for non-intrusive monitoring of high temperature pipes in refineries or nuclear power plants This technology measures directly the actual response and condition of steel structures in selected locations and thus makes possible 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. In addition to offering interesting opportunities within development and industrialization of advanced technology products 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. Ferrx has high ambitions for growth and is always interested in talented engineers. Students interested to do their projects or master thesis are encouraged to contact us. We can offer interesting work in the technical domains of instrumentation systems, material technology, or algorithm development in cooperation with NTNU. Employees will have access to a modern 34-foot sailboat. The boat is used for cruising and racing and employees may participate also as racing crew. DownloadsA Method for Determination of Stress and Fatigue in Risers and Wellheads Contact usFerrx as Brøsetvn 168 N-7069 Trondheim Phone no: +47 40001595 info@ferrx.no |
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