A Method for Monitoring Vibrational Fatigue of Structure and Components

A vibration fatigue monitoring system has been developed by Framatome to assess, in real time, the evolution of industrial structures, systems and components lifetime expectancy. Its originality comes from the fact that only one or a few acceleration measurements are necessary to re-construct the complete stress history in the whole structure, including on welds or bolted connections that could not have been directly instrumented. From this stress history, a fatigue analysis with a rainflow counting algorithm is conducted and the cumulative usage factor of each weld or bolt is determined. The remaining life duration is then estimated. The method has been numerically and experimentally validated in that sense that the reconstructed stress histories were successfully compared to direct stress calculations and measurements. The system was then installed on five industrial structures submitted to transient dynamic excitations. It is expected that it will soon find further applications notably in monitoring vibrations induced during power plants transients that may induce some temporary resonance of piping equipment. Finally, the vibration monitoring system can also be combined with a thermal fatigue monitoring system, many of which are already deployed, at least on nuclear power plants, and the reconstructed stresses might include both thermal and mechanical effects. Installing such a fatigue monitoring on a set of sensitive systems and components could be a valuable brick in the present trend of building digital twins of power plants or other industrial structures.

Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice

The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking was employed in order to represent a supply vessel equipped with a mooring line system, and the realtime loading during the full-scale measurement was recorded. The second vessel Tor Viking was serving as an ice breaker in order to maintain the physical ice management activities with different ice-breaking schemes, i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns were investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Fatigue assessment based both on Rainflow counting and fitted probabilistic models were performed. For the latter, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress ranges represented by application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the Rainflow counting approach. Among the different scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.

An online monitoring method for creep-fatigue life consumption with real-time damage accumulation

Online damage evaluation based on monitored complex cyclic loadings has become an important technique for reliability assessment, especially in high-temperature environments where creep occurs in addition to fatigue. Accuracy and rapidity of calculation are basic requirements for online damage evaluation methods. However, current creep damage evaluation methods seldom consider the fluctuation in stress, which leads to inaccuracy in life-consumption estimates. In addition, traditional cycle-counting methods are not applicable to online use. In this study, an online creep-fatigue damage evaluation method is proposed that accounts for the creep behavior that occurs under fluctuating loads. The cycle-counting method is modified from a rainflow-counting algorithm; it broadens the counting of half-cycles and adopts a new equivalent temperature in the stress-strain response calculation. The proposed method is explained in detail and demonstrated with a case study. The application of this method to a high-temperature, high-pressure pipe demonstrates its online applicability and accuracy. A time-matching algorithm is developed to display the damage evolution in real time, thus revealing the link between the incremental damage and the current load conditions, and yielding an intuitive demonstration of a given component’s state of health.

APPLICATION OF RAINFLOW TECHNIQUES TO THE DESIGN AND OPERATION OF PORT INFRASTRUCTURE

The concept of rainflow comes from the fatigue damage field where it has demonstrated its appropriateness (see Johannesson, 1999). In port engineering, rainflow counting has shown some serious advantages over traditional methods such as the zero-downcrossing method but it is not widely used. This work aims at showing some applications of this technique to problems detected in port operation and reliability after briefly introducing the concept.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/_gwjsDd3yiE

Truck Platooning to Minimize Load-Induced Fatigue in Steel Girder Bridges

Truck platooning has been demonstrated to possess several advantages in relation to energy savings. To implement this technology in the future, a better understanding of the effects of truck platooning on bridges is needed in relation to safety, serviceability, and remaining service life. This research aims at investigating the effects of truck platooning on the fatigue of steel girder bridges. Different types of platoons are simulated in line girder analysis for simple spans and two-equal continuous spans bridges. Then the rainflow counting method is applied to obtain the stress ranges and cycles. Miner’s rule is used to quantify the fatigue damage. The fatigue damage of different platoons is normalized by American Association of State Highway Transportation Officials Load and Resistance Factor Design Fatigue Load for comparison. The effects of the number of trucks and gap distances of truck platoons are further investigated. In some cases, truck platooning helps decrease the fatigue damage since, although truck platooning brings higher load effects, it also decreases the number of cycles. For platoons with different truck wheelbases, there are specific span to wheelbase ratios, beyond which fatigue damage decreases as gap distance increases. In addition, depending on the platoon configurations, there are ranges of span lengths where it is more beneficial to travel as truck platoons rather than traveling individually in relation to fatigue damage.