Mark Cerkovnik - Academia.edu (original) (raw)
Papers by Mark Cerkovnik
Day 1 Mon, May 01, 2017, 2017
The paper provides a review of the state of knowledge regarding the impact of soil response in th... more The paper provides a review of the state of knowledge regarding the impact of soil response in the touchdown point region on Steel Catenary Riser (SCR) fatigue. For almost 20 years the impact of soil-pipe interaction on SCR fatigue has received considerable attention within the offshore geotechnical community. Over this course of time field measurements and a variety of experimental and analytical studies have been performed to determine the soil response necessary to characterize the soil-pipe interaction under long term loading conditions appropriate for fatigue. Little of this work has been integrated into existing codes and standards. This paper will summarize much of the new work to provide better insights on how to address the SCR fatigue problems and to serve as reference for future code modifications.
When risers are designed it is common for corrosion to be accounted for by including a corrosion ... more When risers are designed it is common for corrosion to be accounted for by including a corrosion allowance in the wall thickness [3]. However, when designing risers which are subject to fatigue loading from various sources, simply allowing extra thickness in the wall is inadequate to protect against the accelerated fatigue crack growth driven by corrosion. This paper illustrates a methodology for assessing the fitness for service of a steel catenary riser with various levels of pitting corrosion. The methodology uses FEA tools, as well as classical fracture mechanics, to predict the rates of crack growth and arrive at predictions of life. Once corrosion begins and pits form, the structure may experience an increase in crack growth rate, caused by the influence of the chemistry of the produced fluid on the steel and by the stress effects of the pit geometry. Further complications arise if extreme storms cause riser stresses to exceed yield, which then requires the use of strain based methodology. The results of the illustrative study demonstrate that riser designs should account for the potential of accelerated crack growth where there is a potential for pitting corrosion, and that by only adding a corrosion allowance to account for loss of burst capacity, an inadequate design can easily result.
The in-service fatigue loading of risers may include contributions from first and second order ve... more The in-service fatigue loading of risers may include contributions from first and second order vessel motions, wave loadings, vortex induced vibration (VIV), vortex induced motion (VIM), pressure variation and slugging. All of these loadings are variable amplitude random loadings where the sequence of cycles can change the fatigue outcome. The loading sequence effects can be addressed in analysis through cycle counting methods and through use of the most appropriate methods of damage accumulation. High loads can be responsible for either fatigue crack growth retardation or acceleration depending up loading sequence. The Rainflow Counting method takes into account the whole loading algorithm and assumes the structure memory sustains all through the loading. The Simple Range Count method counts cycles by every single reversals and does not take into account the load sequence or material memory. Fatigue damage accumulation can be accomplished using a linear model like PalmgrenMiner or ...
A methodology is developed to account for the effect of crack face pressure on the reference stre... more A methodology is developed to account for the effect of crack face pressure on the reference stress in high pressure, thick walled, flowlines and risers. A detailed finite element analysis (FEA) is conducted over a range of crack depths (a/t) for long flaws (large crack aspect ratios (2c/a)) for a thick walled pipe (wall thickness/average radius = 0.28). The results from this analysis allows for the implementation of an accurate calculation of the reference stress, for thick walled pipes under high service pressures and temperatures, thereby, allowing an improved fracture prediction.
Applied Ergonomics, 1990
The initial stages of our research on the effects of the overassessment or underassessment of the... more The initial stages of our research on the effects of the overassessment or underassessment of the consequences of nonroutine events (a potentially important factor in decision-making by pilots) is described. Critical difficulties in the measurement of life stress are discussed and a partial solution is suggested in the form of the Life Events Questionnaire (LEQ), an instrument on which individuals report the nature of stressful events, when they happened, and how much they concern them at the time of testing. The results show that the tendency to overassess or underassess the consequences of nonroutine events is consistent within individuals, but is unaffected by life stress levels on the artificial air traffic control simulation used. Analysis of LEQ results showed that high stress subjects had much higher chronic than acute stress scores (p less than 0.001), although the chronic and acute scores were virtually identical for low stress subjects.
Volume 5B: Pipelines, Risers, and Subsea Systems, 2019
The Flexible joint is one of the most widely used hang-off systems for deep water catenary riser ... more The Flexible joint is one of the most widely used hang-off systems for deep water catenary riser for its large rotation and load bearing capacity. The fatigue performance of riser hang-off region and fatigue load on the flexible joint highly depend on the rotational stiffness of the flexible joint. Thus, modelling the flexible joint stiffness to accurately simulate the behavior under cyclic bending cycles is critical in global riser fatigue analysis. The load-displacement relationship of a flexible joint typically follows a nonlinear curve, and it shows hysteresis behavior when subject to cyclic bending cycles. However, in current industry practice, the flexible joint stiffness is modelled either as a nonlinear curve or simplified as a fixed value. These simplified methods sometimes can lead to unconservative or over conservative results in riser design. Modelling the flexible joint stiffness in an accurate approach becomes more important especially when the riser fatigue is critica...
Volume 4B: Pipeline and Riser Technology, 2013
When risers are designed it is common for corrosion to be accounted for by including a corrosion ... more When risers are designed it is common for corrosion to be accounted for by including a corrosion allowance in the wall thickness [3]. However, when designing risers which are subject to fatigue loading from various sources, simply allowing extra thickness in the wall is inadequate to protect against the accelerated fatigue crack growth driven by corrosion. This paper illustrates a methodology for assessing the fitness for service of a steel catenary riser with various levels of pitting corrosion. The methodology uses FEA tools, as well as classical fracture mechanics, to predict the rates of crack growth and arrive at predictions of life. Once corrosion begins and pits form, the structure may experience an increase in crack growth rate, caused by the influence of the chemistry of the produced fluid on the steel and by the stress effects of the pit geometry. Further complications arise if extreme storms cause riser stresses to exceed yield, which then requires the use of strain based...
Volume 1A: Codes and Standards, 2015
In checking the fitness of fatigue critical welded structure, the stress concentration at the wel... more In checking the fitness of fatigue critical welded structure, the stress concentration at the weld due to the weld geometry needs to be considered. Where fatigue is assessed using crack growth methodology, two approaches are commonly used. In the offshore industry in regions where BS 7910 [1] is followed, the effect of weld geometry is assessed using the M k factor approach. The M k factor directly magnifies the stress intensity. M k factor solutions are available for T-butt weld joints from the British Standard BS7910.
Volume 3: Structures, Safety and Reliability, 2015
Drilling and intervention risers are widely used for oil and gas production in deep as well as sh... more Drilling and intervention risers are widely used for oil and gas production in deep as well as shallow waters in oil fields around the world for subsea operations. The risers come in a diverse array of configurations, some of which may be challenged by fatigue if operated in high currents or seastates. The suitability of the selected riser and the operating limits are assessed by conducting strength and fatigue analysis based on design codes such as API RP 2RD, [7], API RP 16Q, [9], and API RP 17G, [10]. Typically, drilling and intervention activities are conducted for short periods of time but used repetitively. The codes are clear about the return period of the design environmental event which must be checked to insure safe operation with respect to strength; however, assessment of fatigue integrity can be more difficult to determine. The allowable fatigue operating environment should account for the ability to disengage, the time required to disengage, the damage rates in particular seastates, prior accumulation of fatigue damage, and variations in soil, tension and internal fluid weights. In this paper, an orderly method of establishing the allowable fatigue operation limits for drilling and intervention risers is presented based on Monte Carlo simulations along with a case study implementing the methodology in a shallow water environment. To illustrate this concept, a riser with wellhead and conductor system is assessed and is subjected to directional loading from several long-term seastates. The variation in effects is studied by doing fatigue analysis for different durations: 3 days, 1 week, 3 months, 1 year and 10,000 hours.
Volume 3: Pipeline and Riser Technology, 2012
Hybrid risers represent an excellent way to isolate the riser from most of the host vessel motion... more Hybrid risers represent an excellent way to isolate the riser from most of the host vessel motions and thereby limit riser fatigue. A common arrangement features the riser supported by a buoyancy can via a tether chain. The tether chain is a cheap simple way to make the connection while providing flexibility for installation. However, in service the tether is under very high tension, and the chain is not really flexible in the face of small amplitude fatigue loads. The friction effectively "welds" the chain together. Moment and torque input to the system by first order vessel motions and vortex induced vibrations are carried through the chain and induce fatigue loading in the links. Analysis of the chain can be problematic because the determination of the detailed stress in the chain requires a refined FEA model with contact element between the links. From the global sense the analysis may require running hundreds of sea-state realizations in the time domain and the vortex induced vibration (VIV) assessment of thousands of current profiles. In this paper an efficient numerical method is described to rigorously determine fatigue damage at locations throughout the chain.
Volume 4B: Pipeline and Riser Technology, 2013
Volume 2B: Structures, Safety and Reliability, 2013
Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines a... more Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines are designed as "nonpiggable", and it is not unusual for an inspection to be incomplete because of physical constraints. As with any measurement, there will be a degree of error. While deterministic conclusions cannot be reached based on such incomplete data sets, probabilistic methods can be used effectively to make judgments about fitness for service. Commonly, different sections along a riser or flowline experience different fatigue spectra and extreme loads. Applying the loads from the sections with the highest loading to all flaws/pits can be too conservative. It is useful to employ statistical methods to assess the probability that a large defect occurs in a region with critical loads. These methods are especially useful when ILI data are incomplete or when estimates of damage must be made based on lines in similar corrosion environments. Properties and parameters other than inspection findings have an element of uncertainty. Fracture toughness, yield stress, and fatigue crack growth rates will be known in terms of mean and standard deviation. Soil properties may be known in terms of upper and lower bound. Likewise, there will be a range of uncertainty about service history and chemical environment. In such cases where fitness for service is based on the interaction of multiple random variables, Monte Carlo methods are appropriate for determining if the probability of failure is sufficiently low to tolerate. In the case of deepwater risers and flowlines where failure could result in loss of containment of hydrocarbons, permissible failure rates are on the order of 1E-5 to 1E-6 per year. This paper examines a riser and a flowline case study. For each case, a fitness for service analysis is conducted using a Monte Carlo simulation to evaluate the probability of failure based on incomplete ILI data and statistical characterization of other pertinent parameters. The results are compared against the conclusions of deterministic analysis.
Volume 4B: Pipeline and Riser Technology, 2013
Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures ar... more Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures are inherently susceptible to vibration because they must be flexible enough to accommodate translation of the flowline, installation tolerances and settlement of pipeline end terminations (PLETs.) In locations where there are bottom currents, the jumpers can be subjected to vortex induced vibrations. When internal flow rates are high, they are susceptible to flow induced vibration, and they may also be excited by slugging. In some cases, the design constraints force the designs to be 3 dimensional and employ strategies to enhance damping. This paper describes a methodology for assessing subsea jumpers for vibration induced fatigue. The method employs a combination of transient dynamic, harmonic and modal finite element analysis with the VIV tool SHEAR7. The methodology is able to show generally improved VIV fatigue lives compared to more traditional methods based on DNV-RP-F105 because of the ability to define current loading over the jumper length and to assess the effects of strakes and coulomb damping. Further, the methodology is also capable of assessing the effect of tuned vibration dampers which are sometimes used to suppress FIV.
Offshore Technology Conference
Day 1 Mon, May 01, 2017, 2017
The paper provides a review of the state of knowledge regarding the impact of soil response in th... more The paper provides a review of the state of knowledge regarding the impact of soil response in the touchdown point region on Steel Catenary Riser (SCR) fatigue. For almost 20 years the impact of soil-pipe interaction on SCR fatigue has received considerable attention within the offshore geotechnical community. Over this course of time field measurements and a variety of experimental and analytical studies have been performed to determine the soil response necessary to characterize the soil-pipe interaction under long term loading conditions appropriate for fatigue. Little of this work has been integrated into existing codes and standards. This paper will summarize much of the new work to provide better insights on how to address the SCR fatigue problems and to serve as reference for future code modifications.
When risers are designed it is common for corrosion to be accounted for by including a corrosion ... more When risers are designed it is common for corrosion to be accounted for by including a corrosion allowance in the wall thickness [3]. However, when designing risers which are subject to fatigue loading from various sources, simply allowing extra thickness in the wall is inadequate to protect against the accelerated fatigue crack growth driven by corrosion. This paper illustrates a methodology for assessing the fitness for service of a steel catenary riser with various levels of pitting corrosion. The methodology uses FEA tools, as well as classical fracture mechanics, to predict the rates of crack growth and arrive at predictions of life. Once corrosion begins and pits form, the structure may experience an increase in crack growth rate, caused by the influence of the chemistry of the produced fluid on the steel and by the stress effects of the pit geometry. Further complications arise if extreme storms cause riser stresses to exceed yield, which then requires the use of strain based methodology. The results of the illustrative study demonstrate that riser designs should account for the potential of accelerated crack growth where there is a potential for pitting corrosion, and that by only adding a corrosion allowance to account for loss of burst capacity, an inadequate design can easily result.
The in-service fatigue loading of risers may include contributions from first and second order ve... more The in-service fatigue loading of risers may include contributions from first and second order vessel motions, wave loadings, vortex induced vibration (VIV), vortex induced motion (VIM), pressure variation and slugging. All of these loadings are variable amplitude random loadings where the sequence of cycles can change the fatigue outcome. The loading sequence effects can be addressed in analysis through cycle counting methods and through use of the most appropriate methods of damage accumulation. High loads can be responsible for either fatigue crack growth retardation or acceleration depending up loading sequence. The Rainflow Counting method takes into account the whole loading algorithm and assumes the structure memory sustains all through the loading. The Simple Range Count method counts cycles by every single reversals and does not take into account the load sequence or material memory. Fatigue damage accumulation can be accomplished using a linear model like PalmgrenMiner or ...
A methodology is developed to account for the effect of crack face pressure on the reference stre... more A methodology is developed to account for the effect of crack face pressure on the reference stress in high pressure, thick walled, flowlines and risers. A detailed finite element analysis (FEA) is conducted over a range of crack depths (a/t) for long flaws (large crack aspect ratios (2c/a)) for a thick walled pipe (wall thickness/average radius = 0.28). The results from this analysis allows for the implementation of an accurate calculation of the reference stress, for thick walled pipes under high service pressures and temperatures, thereby, allowing an improved fracture prediction.
Applied Ergonomics, 1990
The initial stages of our research on the effects of the overassessment or underassessment of the... more The initial stages of our research on the effects of the overassessment or underassessment of the consequences of nonroutine events (a potentially important factor in decision-making by pilots) is described. Critical difficulties in the measurement of life stress are discussed and a partial solution is suggested in the form of the Life Events Questionnaire (LEQ), an instrument on which individuals report the nature of stressful events, when they happened, and how much they concern them at the time of testing. The results show that the tendency to overassess or underassess the consequences of nonroutine events is consistent within individuals, but is unaffected by life stress levels on the artificial air traffic control simulation used. Analysis of LEQ results showed that high stress subjects had much higher chronic than acute stress scores (p less than 0.001), although the chronic and acute scores were virtually identical for low stress subjects.
Volume 5B: Pipelines, Risers, and Subsea Systems, 2019
The Flexible joint is one of the most widely used hang-off systems for deep water catenary riser ... more The Flexible joint is one of the most widely used hang-off systems for deep water catenary riser for its large rotation and load bearing capacity. The fatigue performance of riser hang-off region and fatigue load on the flexible joint highly depend on the rotational stiffness of the flexible joint. Thus, modelling the flexible joint stiffness to accurately simulate the behavior under cyclic bending cycles is critical in global riser fatigue analysis. The load-displacement relationship of a flexible joint typically follows a nonlinear curve, and it shows hysteresis behavior when subject to cyclic bending cycles. However, in current industry practice, the flexible joint stiffness is modelled either as a nonlinear curve or simplified as a fixed value. These simplified methods sometimes can lead to unconservative or over conservative results in riser design. Modelling the flexible joint stiffness in an accurate approach becomes more important especially when the riser fatigue is critica...
Volume 4B: Pipeline and Riser Technology, 2013
When risers are designed it is common for corrosion to be accounted for by including a corrosion ... more When risers are designed it is common for corrosion to be accounted for by including a corrosion allowance in the wall thickness [3]. However, when designing risers which are subject to fatigue loading from various sources, simply allowing extra thickness in the wall is inadequate to protect against the accelerated fatigue crack growth driven by corrosion. This paper illustrates a methodology for assessing the fitness for service of a steel catenary riser with various levels of pitting corrosion. The methodology uses FEA tools, as well as classical fracture mechanics, to predict the rates of crack growth and arrive at predictions of life. Once corrosion begins and pits form, the structure may experience an increase in crack growth rate, caused by the influence of the chemistry of the produced fluid on the steel and by the stress effects of the pit geometry. Further complications arise if extreme storms cause riser stresses to exceed yield, which then requires the use of strain based...
Volume 1A: Codes and Standards, 2015
In checking the fitness of fatigue critical welded structure, the stress concentration at the wel... more In checking the fitness of fatigue critical welded structure, the stress concentration at the weld due to the weld geometry needs to be considered. Where fatigue is assessed using crack growth methodology, two approaches are commonly used. In the offshore industry in regions where BS 7910 [1] is followed, the effect of weld geometry is assessed using the M k factor approach. The M k factor directly magnifies the stress intensity. M k factor solutions are available for T-butt weld joints from the British Standard BS7910.
Volume 3: Structures, Safety and Reliability, 2015
Drilling and intervention risers are widely used for oil and gas production in deep as well as sh... more Drilling and intervention risers are widely used for oil and gas production in deep as well as shallow waters in oil fields around the world for subsea operations. The risers come in a diverse array of configurations, some of which may be challenged by fatigue if operated in high currents or seastates. The suitability of the selected riser and the operating limits are assessed by conducting strength and fatigue analysis based on design codes such as API RP 2RD, [7], API RP 16Q, [9], and API RP 17G, [10]. Typically, drilling and intervention activities are conducted for short periods of time but used repetitively. The codes are clear about the return period of the design environmental event which must be checked to insure safe operation with respect to strength; however, assessment of fatigue integrity can be more difficult to determine. The allowable fatigue operating environment should account for the ability to disengage, the time required to disengage, the damage rates in particular seastates, prior accumulation of fatigue damage, and variations in soil, tension and internal fluid weights. In this paper, an orderly method of establishing the allowable fatigue operation limits for drilling and intervention risers is presented based on Monte Carlo simulations along with a case study implementing the methodology in a shallow water environment. To illustrate this concept, a riser with wellhead and conductor system is assessed and is subjected to directional loading from several long-term seastates. The variation in effects is studied by doing fatigue analysis for different durations: 3 days, 1 week, 3 months, 1 year and 10,000 hours.
Volume 3: Pipeline and Riser Technology, 2012
Hybrid risers represent an excellent way to isolate the riser from most of the host vessel motion... more Hybrid risers represent an excellent way to isolate the riser from most of the host vessel motions and thereby limit riser fatigue. A common arrangement features the riser supported by a buoyancy can via a tether chain. The tether chain is a cheap simple way to make the connection while providing flexibility for installation. However, in service the tether is under very high tension, and the chain is not really flexible in the face of small amplitude fatigue loads. The friction effectively "welds" the chain together. Moment and torque input to the system by first order vessel motions and vortex induced vibrations are carried through the chain and induce fatigue loading in the links. Analysis of the chain can be problematic because the determination of the detailed stress in the chain requires a refined FEA model with contact element between the links. From the global sense the analysis may require running hundreds of sea-state realizations in the time domain and the vortex induced vibration (VIV) assessment of thousands of current profiles. In this paper an efficient numerical method is described to rigorously determine fatigue damage at locations throughout the chain.
Volume 4B: Pipeline and Riser Technology, 2013
Volume 2B: Structures, Safety and Reliability, 2013
Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines a... more Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines are designed as "nonpiggable", and it is not unusual for an inspection to be incomplete because of physical constraints. As with any measurement, there will be a degree of error. While deterministic conclusions cannot be reached based on such incomplete data sets, probabilistic methods can be used effectively to make judgments about fitness for service. Commonly, different sections along a riser or flowline experience different fatigue spectra and extreme loads. Applying the loads from the sections with the highest loading to all flaws/pits can be too conservative. It is useful to employ statistical methods to assess the probability that a large defect occurs in a region with critical loads. These methods are especially useful when ILI data are incomplete or when estimates of damage must be made based on lines in similar corrosion environments. Properties and parameters other than inspection findings have an element of uncertainty. Fracture toughness, yield stress, and fatigue crack growth rates will be known in terms of mean and standard deviation. Soil properties may be known in terms of upper and lower bound. Likewise, there will be a range of uncertainty about service history and chemical environment. In such cases where fitness for service is based on the interaction of multiple random variables, Monte Carlo methods are appropriate for determining if the probability of failure is sufficiently low to tolerate. In the case of deepwater risers and flowlines where failure could result in loss of containment of hydrocarbons, permissible failure rates are on the order of 1E-5 to 1E-6 per year. This paper examines a riser and a flowline case study. For each case, a fitness for service analysis is conducted using a Monte Carlo simulation to evaluate the probability of failure based on incomplete ILI data and statistical characterization of other pertinent parameters. The results are compared against the conclusions of deterministic analysis.
Volume 4B: Pipeline and Riser Technology, 2013
Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures ar... more Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures are inherently susceptible to vibration because they must be flexible enough to accommodate translation of the flowline, installation tolerances and settlement of pipeline end terminations (PLETs.) In locations where there are bottom currents, the jumpers can be subjected to vortex induced vibrations. When internal flow rates are high, they are susceptible to flow induced vibration, and they may also be excited by slugging. In some cases, the design constraints force the designs to be 3 dimensional and employ strategies to enhance damping. This paper describes a methodology for assessing subsea jumpers for vibration induced fatigue. The method employs a combination of transient dynamic, harmonic and modal finite element analysis with the VIV tool SHEAR7. The methodology is able to show generally improved VIV fatigue lives compared to more traditional methods based on DNV-RP-F105 because of the ability to define current loading over the jumper length and to assess the effects of strakes and coulomb damping. Further, the methodology is also capable of assessing the effect of tuned vibration dampers which are sometimes used to suppress FIV.
Offshore Technology Conference