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Game-changing technology for integrity monitoring of steel structures |
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How it works
FATIGUEFatigue 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: accumulation of cyclic plastic deformation which is closely related to bulk material properties, formation of slip bands and nucleation and growth of microcracks in the surface, and finally growth of a macroscopic crack to failure. Measure fatigueThe material changes during a fatigue process cause typically reduced permeability and an increase of electrical resistance in the surface. These changes in the outer surface and beneath are monitored by the FEMM's transient voltage response. This response changes according to the degree of changes in these parameters, e.g. when micro-crack density increases and grows to more continuous cracks, the response signal changes accordingly. By analyzing the response signal, changes of permeability and 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 developmentMeasure stressesStress measurements in ferromagnetic steel are relative to a previous measurement, preferably taken with known stress levels. Calibration curves can be established and quantification of actual stress level is thus possible.Plasticity, permanent changes in the material caused by stress exceeding yield, is detected. This is, for example , observed when monitoring areas with residual stress. Changes of residual stresses related to welds are measured with sensitivity also for changes in depth location. 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 measurement, and the permanent change can then be measured. Differentiation between these changes are related to the analyses of changes of permeability and resistance and the depth of these changes. This has been verified by several high cycle fatigue tests and miscellaneous measurements of elastic and plastic stresses. Measure cracksThe pin 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. The matrix sensing 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.CORROSIONCorrosion internal in pipelines is more or less uneven and the degree of corrosion attack can vary 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 and degree of attacks. Measure corrosionThe location expected to be most exposed to corrosion is selected for installation of the FEMM 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 and installed. The whole area covered by the sensing matrix is monitored for any internal metal loss. Initially, a measurement is taken and stored and used as a reference for the following measurements, which give the change due to corrosion attacks. When significant 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 signal.EROSIONErosion internal in pipes 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 bend geometry and flow. Both carbon steel and duplex steel can be monitored. Measure erosionThe sensing pin matrix is designed for optimized sensitivity based on expected shape of erosion, e.g. if erosion is wide and in outer radius, the matrix is distributed along the outer radius. If the erosion is expected to be a narrow groove along the outer radius the matrix can be along the bend'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 4 different matrices which can be located to monitor 4 separate erosion locations. When significant metal loss is detected, the actual depth of the deepest attack within an matrix can be estimated based on the patented FEMM algorithm. |
SYSTEM CONCEPTS![]() |
A FEMM system consists of four main modules: the sensor arrangement on the steel structure, the sensor interface unit, the data acquisition unit, and the dedicated PC SW. This modularity provides for extensive flexibility to optimize the system configuration and performance for many applications. This 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 structure. |
Sensors and all fixed installed components shall have the same operational lifetime as the monitored structures and 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 bridge up to 32 cracks within 20m from the data acquisition unit. |
System Components
The FEMM technology has been designed with flexibility for different applications onshore, topside, and subsea. Electronics and software designs are similar for all applications. The sensor pin layout, instrument encapsulations and software configuration are selected for the actual application.
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The sensor
The picture shows an example of sensor layout for monitoring a pipe buttweld, and for monitoring defects both in outer and inner surfaces of the pipe wall. The sensor comprises the sensing pins and the excitation current, both requiring electrical contact with the steel. One or more temperature sensors monitor the structure's surface temperature. The Sensor Interface (SI) cylinder shown above on the right comprises the interfacing and digitizing circuits and the current excitation circuits.
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Sensor interfaceThe Sensor Interface (SI) unit contains signal conditioning and digitalization circuits and a high current excitation circuit. Each unit handles up to four matrices with a total of 28 sensing pin pairs and four pairs for current excitation. Communication with the instrument is linked via a multidrop digital bus, with up to eight SI units (altogether 224 pin pairs) on one cable per instrument. The picture shows SI encapsulation for use in onshore applications. (IP68). |
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Portable instrument
This instrument is used for examination of a number of inspection points (tags) fitted with pin matrices and Sensor Interfaces. The configuration setup for all tags to be measured are downloaded from the PC SW to the instrument before the inspection tour. Data from all tags are intermediately stored until downloaded to the PC SW. In this way, a high number of inspection points can be evaluated at low cost. The instrument is powered by a rechargeable battery. |
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Autonomous instrument
This data acquisition unit for autonomous monitoring in harsh environment is powered by an internal battery or by external power. Operation is offline or online, by cable or wireless for real-time condition data. Miscellaneous protocols are available.
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Subsea integrated sensor and SI protection
The left sketch shows sensor installation on an 8-inch riser pipe with a subsea SI unit included. The encapsulation is adapted to the size of the monitored area and available space. A robust composite shell filled with soft silicone rubber protects the instrumentation fixed to the pipe. The shell gives sufficient impact protection during handling and deployment.
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About Ferrx
Ferrx is an independent company located in Trondheim, Norway with the business idea to provide the FEMM technology for different onshore and offshore markets. This technology monitors the actual condition of steel structures and thus can prevent loss of assets and pollution of the environment. The Ferrx FEMM has been developed and tested for two decades, first by SINTEF and since 2005 by Ferrx with the support from several oil companies, Innovation Norway and The Research Council of Norway.
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DownloadsA Method for Determination of Stress and Fatigue in Risers and Wellheads ResourcesFerrx appreciates 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. Leisure activitiesEmployees 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.VacanciesFerrx has high ambitions for growth and is always interested in talented engineers. We can offer interesting work in the technical domains of instrumentation systems, material technology, electromagnetic modeling and simulation.
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Contact page |
For more information, please contact us at: Ferrx as Brøsetvn 168 N-7069 Trondheim Norway Phone no: +47-40001595 ![]() |
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