Conference Paper

Safety Factors and Innovation in Ropes and Cables

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... Alternatively, in designing for endurance, an equal performance with a lower diameter rope can also be obtained. Based on fundamental understanding of HMPE rope behavior, endurance data, models and methods, proper engineering will result in smaller diameter ropes, that are fit for purpose, safe and reliable, with similar lifetime expectancy compared to standard ropes [8]. Rope diameter reduction of approximately 15% seems to be possible. ...
Conference Paper
Tension fatigue lifetime of high modulus polyethylene, HMPE, fiber is governed by plastic deformation (creep) failure. Testing confirms that high creep resistant HMPE fiber types have longer tension fatigue life. The applicability of a damage summation rule was investigated for variable static load conditions on fibers and a variable dynamic load condition on a rope. The contribution of each of the varying load periods can be described by summation of permanent elongation. The result from these periods determines the final lifetime.
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Modern fiber ropes have several distinctive properties which predestine them amongst others for high dynamic applications in robotics. Beside their great breaking load due to their high tensile streghth, the extremely low density and weight are the most important advantages over steel wire ropes. For steel wire ropes, it is generally known that their lifetime drops when raising the dynamic stress on running or static ropes. The long-time behavior of high-dynamically stressed fiber ropes is totally unexplored up to now. This lack impedes the breakthrough of fiber ropes and causes a safety gap, which has to be closed. This paper describes the research on modern fiber ropes regarding their lifetime in normal and high dynamic applications. The derived results are interpretered with respect to application in robotics.
Conference Paper
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The topic of care and maintenance, including inspection and testing, of climbing and safety ropes is very important to climbers and workmen who wish to avoid unsafe and possibly life-threatening situations. For this reason, the following paper examines how climbing and safety ropes degrade in various environments, and to a limited extent how they can be maintained, inspected and tested to avoid unwanted mishaps, injuries, and deaths. The main focus of this paper is the dynamic kernmantle rope used for climbing. Dynamic ropes are specially engineered and manufactured to elongate as much as 30% under loading so the kinetic energy of the climber can be slowly absorbed by the rope and thus reduce the impact at the bottom of the fall. Because these and most other ropes are used mainly outside, the primary forms of degradation/corrosion examined are abrasion, erosion, heat- and UV-aging, and accidental or inadvertent cutting. These ropes are not constantly exposed to corrosive environments as they are used while climbing then conveyed home by various means and typically stored indoors by the owner. Hence to prevent, detect, and monitor serious and suspect aging damage to ropes, storage locations, coiling techniques, and currently available testing and inspection techniques are presented. Some common inspection and testing techniques as well as at least one novel technique are presented and discussed. Currently climbers inspect for damage and defects using both tactile and visual methods by simply pulling the rope, meter by meter, through one's hand while scanning the length visually as it passes. Damage and defects are evaluated by climber experience and guesswork and noted by memory or recorded if desired. However, a major problem results because of the unique and valuable design and construction feature of these kernmantle ropes - the major load carrying core strand members are both hidden from view and protected from UV and mechanical damage by a powerful external she- ath of continuous webbing. Clearly damage can occur to both the sheath and the core but finding the weakest link in the hidden core provides the major challenge. Hence this paper also examines the need for more certainty in non-destructive testing, inspection instruments, and methods of detecting, locating, and defining damages. These inspection methods will also evaluate risk degree and monitor/track defects and damage in such ropes. Two narrow ultimate goals are to find the rope's ?weakest link? and to know, predict, or determine when to retire such ropes in order not to go below a certain factor of safety in use. Recognizing that much valuable work has been done to try to attain this goal and that this goal remains substantially unattained, this paper also proposes a proof testing program to evaluate the efficacy of the classic and novel testing and inspection methods. Using the proposed testing program, the ropes could be examined for internal flaws and characterized by remaining life-span with a certain factor of safety, and thus they could be used longer, more effectively, and more safely than currently possible. Some of the technical inspection and maintenance techniques suggested and discussed will relate to classical and modified methods of measuring the most informative mechanical, dimensional, physical, and viscoelastic properties along the length of these ropes.
Conference Paper
Tension-tension fatigue tests on high modulus polyethylene fibers show that fatigue lifetime is governed by plastic deformation failure. This insight is further evaluated on small ropes and via a simple to implement dynamic shift factor, time-to-failure under dynamic conditions is shown to be predicted based on static creep failure. Basis of the shift factor is the time spend under load and gives excellent predictions when no additional heating-up is introduced during the test. This makes DSM Dyneema's Performance Model, for static creep prediction, also capable to predict dynamic tension-tension failure.
Cyclic bending over sheave fatigue tests on braided ropes of high modulus polyethylene fibers were carried out for developing a better understanding of their failure. Damage accumulation at strand cross-over locations was identified as the main failure mechanism. At these locations, strands repetitively bend and slide over each other under high contact pressure. The application of a DSM proprietary finish termed XBO markedly improved the braid lifetime. This is attributed to the friction and adhesion lowering properties of the finish. The damage accumulation process in the filaments was studied in more detail in a filament friction test. This test showed that the filament gets damaged gradually over its whole volume and not only close to the contact surface.
Conference Paper
Under constant loading HMPE fibers and ropes show an irreversible deformation (creep) behavior that is strongly dependent upon load and temperature. This paper presents an updated model that seeks to accurately predict the creep rate at various temperature ranges and to estimate creep life of HMPE on fiber level, and demonstrates the apparent validity of this model to rope applications regardless of rope construction. The model may thus serve as design tool for long-term loading conditions as are found in offshore mooring operations
The Mad dog project will use a polyester mooring system on the drilling and production truss spar. This will be the first use of a permanent polyester mooring system on a Floating Production System (FPS) outside of Brazil and the first time polyester has been used on a spar. As such, there were many challenges, which include:•Regulatory approval.•Designing a mooring system which is dominated by current loadings.•Largest polyester rope break load ever required.•Rope design qualification and testing.•Quality control and assurance.•Inspection, Maintenance, Repair and Retirement (IMRR) of such a mooring system.This paper will focus on the design issues, rope design, manufacturing, qualification and testing, and the IMRR plan that was developed to provide the assurance that the polyester mooring system could be safely operated over the 20-year field life.
A method has been developed for measuring infrared spectra during the mechanical deformation of yarns. This rheooptical technique was applied to study the molecular processes that take place along the stress-strain curve of PET yarns. The results were combined with data obtained from size exclusion chromatography (SEC) and tensile measurements at elevated temperatures. The results indicate that the first modulus maximum marks the breakdown of the amorphous entanglement network and the start of molecular uncolling by gauche → trans transitions. In addition, stress develops on the crystals and particularly on tie molecules with a short contour length in the amorphous domains. Ultimately, molecular fracture of taut-tie molecules causes the modulus to pass through a second maximum. The chain ends of broken molecules recoil by trans → gauche transitions. Local stress accumulation will lead eventually to yarn rupture. © 1993 John Wiley & Sons, Inc.
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There is considerable diversity in fiber ropes, both in construction, material and quality. Applications for high performance ropes are expanding rapidly and engineering data may be limited. Selection can be a difficult process. Once in service the effects of frequent use, age, wear and abuse are difficult to evaluate. This paper will give suggestions on how to approach selection of a rope product for new applications. This will be followed by guidelines on how to evaluate its continued serviceability. This second portion of the presentation will be based on a recently released document by the Cordage Institute, CI 2001-04, 'Fiber Rope Inspection and Retirement Criteria'.
Conference Paper
Nondestructive testing for synthetic fibre ropes is an important step to ensure their safe use as mooring lines for offshore floating platforms. OSCAR is an acronym derived from Optical Scanning Apparatus for Ropes. OSCAR is a new, nondestructive system that has been developed using an optical fibre transducer and a measurement technique known as Brillouin scattering. This is a distributed method and allows changes in the length to be detected along entire length of the optical fibre. It consists of the Brillouin Optical Time Domain Reflectometer (BOTDR) and the optical fibre transducer. The optical transducer is built into the rope in such a way that it elongates with the rope elongation. The transducer's fibres are connected to the BOTDR which detects the resultant elongation in the optical fibres. As the rope wears or is damaged there is both general and local loss of strain bearing synthetic fibre with a corresponding increase in elongation. When the elongation becomes excessive the rope is retired. This paper describes the system and presents the results of the system testing.
Conference Paper
A great many specifications, engineering guides and test results relating to polyester mooring ropes have been published. Now, in 2001, this type of rope is being introduced in the Gulf of Mexico. One recent area highlighted is how to inspect ropes in service and what measures need to be taken when minor damage occurs. This article proposes a test method to measure the Assured Residual Life Span (ARELIS) of a mooring rope. This method is based on an idea proposed by Coleman in the 1950s and worked out by Zhurkov in the 1960s. They argued that structural molecular changes (in this report indicated by the "Damage" parameter) occur throughout the lifetime of a polymeric sample. The ARELIS can be tested using a short creep test at a higher than normal load on a sub-rope of a mooring rope insert. The effect of storms can also be taken into account. For a parallel rope construction the effects of reduced load bearing area due to cuts can be predicted. The simplest method of compensating for visual damage in the short term, without undermining the inserts ARELIS test plan, is to reduce pretension
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