Structural Analysis and Load Monitoring of a Loss of Tension Incident

Monitoring of riser motion and loads is increasingly being used to assess metal fatigue and to assist rigs in operating safely. Monitoring systems provide valuable information on unexpected incidents. This paper shows how sensor data have been used in combination with structural analysis to assess consequences of a loss of tension for a top-tensioned CWO riser. In order to avoid that a single failure in a tensioning system causes total loss of tension and riser buckling risers should be operated using both rucker tensioners and top drive. However, prior to the retrieval of the riser only top tension was applied. Due to a power out the top drive tension was lost, and the resulting set down caused the riser to buckle. The consequence could in the worst case have been permanent damage to key riser components such as the Lower Tapered Stress Joint and Weak Link. However, as the riser was equipped with a monitoring system that provided accurate data on deformation at key locations, it was possible to show that the system had not been exposed to permanent deformations and could be safely used further. It is advisable to perform continuous monitoring of tension and put in place mitigation to avoid that such incidents lead to permanent damage in the future.

Investigation of Low-Cycle Fatigue on Structural Carbon Steel

It is possible to explain the phenomenon of fatigue destruction and the patterns that are observed only in the deep study of the processes taking place in the material under conditions of repeated-variable loading, i.e. in the development of the physical theory of metal fatigue. Despite the large number of work on this issue, there is currently no single interpretation of the process of fatigue destruction of metals, which is primarily due to the exceptional complexity of the problem. The purpose of the study is to study low-cycle corrosion fatigue of steel using the example of A 414 Grade A steel. The work solved problems, such as research of kinetics of crack development in conditions of low-cycle loading of metal structure made of carbon structural steel A 414 Grade A. Regression analysis has also been applied to predict a change in the thermodynamic stability of the metal during cyclic loading. Analysis of fatigue crack development at alternating loading cycle was carried out. The results of calculations based on the proposed model of elastoplastic deformation near the top of the crack at the sign-alternating loading cycle can be described by non-linear dependence. The regression analysis revealed that the correlation coefficient of the selected model is-0.93, which indicates a relatively strong relationship between the variables. In experimental way it has been proved that reduction of thermodynamic stability of metal in corrosive medium is connected with increase of number of loading cycles, which leads to accumulation of fatigue damages.

Are super-long escalators safe? Lessons learned from the Langham Place escalator incident in Hong Kong

Super-long escalators that are increasingly used in mega-cities take up a large number of passengers, and so their risk of sudden failure draws serious attention. As a case study, on 25 March 2017, an escalator with a 21 m elevation in Hong Kong’s Langham Place had its main drive chain suddenly snapped by metal fatigue, causing the escalator to reverse at an accelerating speed. A number of passengers were injured. In this paper, two issues will be discussed: (1) whether metal fatigue of the main drive chain can be detected with conventional protocols, and (2) what safety factor is needed to prevent metal fatigue. Analysis shows that initial fatigue cracks in escalator drive chains may not be easily detected with the commonly adopted maintenance protocol. Also, the time window from the emergence of clear signs of fatigue failure to the sudden snapping of the drive chain may be as short as weeks or even days, versus the common safety inspection intervals of six months. The safety factor to prevent metal fatigue of the drive chain should be at least 7, whereas lower values are currently allowed. It is suggested that the government should review the legal requirements to meet the recommended value.

Short/small fatigue crack growth, thresholds and environmental effects: a tale of two engineering paradigms

This paper results from mutual discussions on the review ‘When do small fatigue cracks propagate and when are they arrested?’ in Corrosion Reviews, 2019; 37(5): 397–418. These discussions have arisen from the two engineering paradigms characterizing our fatigue research: (i) an aerospace research and technology remit for metallic airframes, and (ii) a materials science research programme supporting a methodology for steam turbine low pressure (LP) blade operations. In our opinion, this paper is of interest for other investigators of metal fatigue with respect to design requirements, life predictions and assessments. In more detail, the paper considers the fatigue design methodologies for airframes and steam turbine LP blades. This includes short/small fatigue cracks, fatigue crack growth thresholds, high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF), and the relevance of environmental effects (corrosion and corrosion fatigue).

The Evaluation of Front Shapes of Through-the-Thickness Fatigue Cracks

Fatigue failure of structural components due to cyclic loading is a major concern for engineers. Although metal fatigue is a relatively old subject, current methods for the evaluation of fatigue crack growth and fatigue lifetime have several limitations. In general, these methods largely disregard the actual shape of the crack front by introducing various simplifications, namely shape constraints. Therefore, more research is required to develop new approaches to correctly understand the underlying mechanisms associated with the fatigue crack growth. This paper presents new tools to evaluate the crack front shape of through-the-thickness cracks propagating in plates under quasi-steady-state conditions. A numerical approach incorporating simplified phenomenological models of plasticity-induced crack closure was developed and validated against experimental results. The predicted crack front shapes and crack closure values were, in general, in agreement with those found in the experimental observations.

METHODS FOR THE SCHEMATIZATION OF THE OPERATIONAL LOADING OF THE FREIGHT CAR

The world trend, recently, is the creation of a high-speed cargo rolling stock for speeds with 160 km / h. In these condition, the durability of the structure of the cargo car are relevant. In the process of movement in the design of the car, voltages occur, variables in time. Under the action of alternating voltages in the design elements, the process of gradual accumulation of damage, leading to the formation of microscopic crack, and then to its development and subsequent sudden destruction - metal fatigue. One of the main properties of the wagon is the ability to withstand operational loads acting on it while maintaining this ability without destruction at all stages of the life cycle. The assessment of the bearing capacity is determined by the results of the undercarriage tests, the purpose of which is the definition and assessment of the reserve coefficient of fatigue resistance of the equivalent reduced amplitude of dy-namic stresses. As a rule, dynamic stresses are random due to the perturbing effect on the side of the rail path on the wheeled pairs, which are also random. Therefore, an important section of the study is the choice of methods for obtaining, processing and analyzing experimental data. Improving the reliability of test results is achieved by applying more advanced recording methods and processing results. To estimate the level of loading of the cargo car, methods are used based on the replacement of a real random process by some schematized process, which in terms of the accumulation of fatigue damage should be equivalent to a real process. Of the variety of schematics methods, two methods are distinguished - the method of complete cycles and the rain method, which most fully reflect the real process. The advantage of the "rain" method is the ability to process the process in real time. However, the algorithm of the "rain" method is quite complicated and does not allow processing large amounts of information. In this regard, the method of maximum discharges was proposed, which is a type of full cycles method and allows you to process an unlimited amount of information online. The schematic process is divided into classes - voltage amplitudes values. Depending on the distribution of voltage amplitudes in classes, the frequency (probability) of amplitude in the class is established. The reduced amplitude of the dynamic voltage is defined as the amount of products of the likelihood of entering each class on the average magnitude of the voltage amplitude in the class. Key words: cargo car, process, dynamic, voltage, amplitude.

Methods to improve the efficiency of the business process of repairing power-generating equipment

The paper considers the methods to improve the efficiency of the business process of repairing power-generating equipment, as one of the main directions for increasing the efficiency and safety of the company activity as a whole. The efficiency of power generating companies is currently determined by the quality of the field-oriented and supporting business processes arrangement. Companies in the power-generating sector have strict environmental and energy security requirements. Accidents at production and transport facilities can cause irreparable environmental deprivations. Also, the failure of the mains sections can completely stymie the work of large settlements, and endanger the life and health of people in the cold season. The performance of the equipment can be impaired as a result of natural causes (corrosive wear, metal fatigue, and other deformations) and due to violation of the operating mode. The good condition of the processing equipment is ensured by the maintenance and repair works performed in time. Company's experience has proven that, for the safe operation of processing equipment, it is necessary to annually appropriate funds in the amount of at least 2% of the initial cost of the equipment. The main focus should be on planning and arranging the processes involved. Safe operation can also mean availability to purchase equipment necessary for production tasks. Many large power generating companies are trying to act under the principle of technological self-sufficiency. It implies the presence of technological developments in intellectual property, as well as production facilities. The implementation of this principle is possible both through the development of own scientific resources, and through the absorption of industrial enterprises. All this gives a competitive advantage to power generating companies, as well as expands the range of services provided.