Relationships Between Mechanical Properties and the Extension and Arrest of Unstable Cracks in Line Pipe Steels

1980 ◽  
Vol 102 (3) ◽  
pp. 309-313 ◽  
Author(s):  
A. K. Shoemaker
Keyword(s):  
Transmission Lines ◽  
Large Diameter ◽  
Fracture Initiation ◽  
Crack Arrest ◽  
Crack Size ◽  
Operating Conditions ◽  
Design Parameters ◽  
Critical Crack ◽  
Line Pipe ◽  
Stress Dependent

With the increasing need for high-strength, high-pressure, large-diameter, gas-transmission lines, considerable attention has been given, in recent years, to the aspects of fracture initiation, propagation and crack arrest in line pipe. This paper presents an overview of the interrelations between material properties and design parameters that can lead to the initiation of a running fracture and the interrelationships which are necessary to arrest a running fracture. It is shown that if the pipe has ductility such that CVN/YS ≥ 0.6 ft-lb/ksi, further increases in Charpy toughness would not have a significant effect upon the critical crack size because fracture initiation becomes flow-stress dependent. Moreover, the length of a stable through-the-wall crack at operating conditions would be about two orders of magnitude longer than the current rejectable weld defect length specified by API. For “conventional” transmission-line applications CVN ≥ 0.024 σh1.5D0.5 assures arrest of running shear fractures.

Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

2012 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida
Keyword(s):  
Evaluation Method ◽  
Large Diameter ◽  
Crack Size ◽  
Evolution Model ◽  
Piping System ◽  
Rotational Stiffness ◽  
Critical Crack ◽  
Rotational Spring Model ◽  
Size Evaluation ◽  
Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

Reliability Analysis of a Pre-Cracked Structure in Accidental Operation Conditions

2019 ◽  
Vol 820 ◽  
pp. 188-202
Author(s):  
Mohammed Amine Belyamna ◽  
Abdelmoumene Guedri ◽  
Racim Boutelidja
Keyword(s):  
Fracture Mechanics ◽  
Large Diameter ◽  
Small Diameter ◽  
Crack Size ◽  
Initial Crack ◽  
Operating Conditions ◽  
Seismic Load ◽  
Large Diameter Pipe ◽  
Operation Conditions ◽  
Diameter Pipe

Evaluating the integrity of a structure consists in proving its ability to realize its mechanical functions for all modes of loading, normal or accidental, and throughout its lifetime. In the context of nuclear safety, the most important structures consider the presence of a degradation grouping several aspects, such as cracks. In this context, the fracture mechanics provide the tools needed to analyze cracked components. Its purpose is to establish break criteria for judging loading margins in normal or accidental operating conditions. The seismic load is one of the dominant loads for the failure assessment of the pipes. Its probabilistic dispersion, however, was not taken into account in the past probabilistic fracture mechanics analysis. The objective of this paper is to simulate and analyze the effect of abnormal stress on the reliability of tow pipe sizes. As result the seismic stress has more effect on the break probability, but not for the leak probability. In the case without a seismic load, the break probability is mainly dominated by an initial crack size. The earthquake has much effect on the break probability for the large diameter pipe, not for the small diameter pipe. In the large diameter pipe, the break probability increases gradually with the time. The leak probability of both pipe sizes is not affected by the seismic curve.

Crack Initiation in 14% Cr Low Pressure Turbine Blade Steel

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
W. Hahn ◽  
G. Tasker ◽  
E. Naylor ◽  
M. Kidd
Keyword(s):  
Crack Initiation ◽  
Function Analysis ◽  
Damage Model ◽  
Low Pressure ◽  
Crack Size ◽  
Operating Conditions ◽  
Significant Shift ◽  
Critical Crack ◽  
Accumulated Damage ◽  
The Impact

The impact of multiple erosion pits and crack initiation was investigated for a 500 megawatt (MW) steam turbine unit with three low pressure (LP) rotors on the steam end and generator end of the stage L0 blades. These units have been subjected to two-shifting operation and have been retrofitted with new high pressure (HP) turbine units over the life history of the turbines. Droplet erosion damage was exacerbated by operating conditions causing multiple crack initiation sites concentrated above the root platform. A method of accumulated damage was employed using pit counting and the number of cycles referenced back to turbine revolutions in line with the accumulated damage model developed from the damage function analysis and Palmgren–Miner approaches. The number of rotational cycles were calculated from the starts and running hours for pre- and post-retrofit scenarios and compared and correlated to the number of pits formed during the completed cycles. The macro crack size represented the critical crack size or a damage number of one. It was found that there was a significant shift in the number of rotations before and after the HP turbine retrofit to achieve a damage rate of one. An accumulated damage model was developed for the post HP turbine retrofit and the LP turbine last stage blades fitted from new, based on the empirical evidence from the analysis. Assessments on the erosion distribution in the zoned areas revealed evidence of cracking, manifesting 18 mm away from the highest probability distribution with a standard deviation of 2 mm. The area where cracking first initiated on multiple samples was found to coincide with the mechanical change in the section blending in with the blade trailing edge. The damage model was implemented on a ive running plant and successfully applied over a period of two years using the most conservative approach, based on the lower bound values.

Probabilistic Fracture Analysis of Pipelines

2002 ◽  
Author(s):  
Shahani Kariyawasam ◽  
Mark Stephens ◽  
Wytze Sloterdijk
Keyword(s):  
Fracture Initiation ◽  
Crack Arrest ◽  
Small Samples ◽  
Mixed Mode Fracture ◽  
Line Pipe ◽  
Initiation And Propagation ◽  
Probabilistic Characterization ◽  
Fracture Control ◽  
Added Uncertainty

Many pipelines were built before the industry developed material specifications for fracture control. For these older pipelines an essential first step in fracture control is to estimate the existing likelihood of fracture initiation and propagation. It is also desirable for operators to know the size of defects the pipeline can tolerate without causing pipeline fracture. This paper describes a methodology developed for the probabilistic characterization of the fracture initiation and propagation susceptibility of older pipeline segments, made from line pipe exhibiting (by today’s standards) low to moderate strength and low notch toughness. It is applicable to ductile, brittle and mixed-mode fracture behaviour. A probabilistic analysis approach is ideally suited to the problem since it offers a way to quantitatively address both the inherent variability in the mechanical properties of line pipe and the uncertainties associated with the various models currently available to determine the conditions necessary to cause crack initiation or to force crack arrest. The method described addresses both of these forms of uncertainty, and also reflects the added uncertainty inherent in trying to estimate material properties for existing lines from small samples of data.

Establishing and Satisfying Thermal Requirements for Drilled Shaft Concrete Based on Durability Considerations

2021 ◽  
pp. 036119812199635
Author(s):  
Andrew Z. Boeckmann ◽  
Zakaria El-tayash ◽  
J. Erik Loehr
Keyword(s):  
Mechanical Response ◽  
Large Diameter ◽  
Thermal Cracking ◽  
Drilled Shafts ◽  
Maximum Temperature ◽  
Design Parameters ◽  
Mass Concrete ◽  
Temperature Differential ◽  
Thermal Requirements ◽  
Ettringite Formation

Some U.S. transportation agencies have recently applied mass concrete provisions to drilled shafts, imposing limits on maximum temperatures and maximum temperature differentials. On one hand, temperatures commonly observed in large-diameter drilled shafts have been observed to cause delayed ettringite formation (DEF) and thermal cracking in above-ground concrete elements. On the other, the reinforcement and confinement unique to drilled shafts should provide resistance to thermal cracking, and the provisions that have been applied are based on dated practices for above-ground concrete. This paper establishes a rational procedure for design of drilled shafts for durability requirements in response to hydration temperatures, which addresses both DEF and thermal cracking. DEF is addressed through maximum temperature differential limitations that are based on concrete mix design parameters. Thermal cracking is addressed through calculations that explicitly consider the thermo-mechanical response of concrete for predicted temperatures. Results from application of the procedure indicate consideration of DEF and thermal cracking potential for drilled shafts is prudent, but provisions that have been applied to date are overly restrictive in many circumstances, particularly the commonly adopted 35°F maximum temperature differential provision.

A phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines

2020 ◽  
Vol 21 (4) ◽  
Author(s):  
Nishant Kothari ◽  
Bhavesh R. Bhalja ◽  
Vivek Pandya ◽  
Pushkar Tripathi ◽  
Soumitri Jena
Keyword(s):  
Transmission Lines ◽  
Power Flow ◽  
Detection Algorithm ◽  
Current Transformer ◽  
Operating Conditions ◽  
Fault Classification ◽  
Phase Detection ◽  
Parallel Transmission ◽  
Classification Technique ◽  
Computational Requirement

AbstractThis paper presents a phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines. Detection and classification of faulty phase(s) have been carried out by deriving indices from the change in phasor values of current with a distance of one cycle. The derived indices have zero values during normal operating conditions whereas the index corresponding to the faulty phase exceeds the pre-defined threshold in case of occurrence of a fault. A separate ground detection algorithm has been utilized for the identification of involvement of ground in a faulty situation. The performance of the proposed technique has been evaluated for intra-circuit, inter-circuit and simultaneous faults with wide variations in system and fault conditions. The suggested technique has been evaluated for over 23,000 diversified simulated fault cases as well as 14 recorded real fault events. The performance of the proposed technique remains consistent under Current Transformer (CT) saturation as well as different amount and direction of power flow. Moreover, suitability to different power system network has also been studied. Also, faults having fault current less than pre-fault conditions have been detected accurately. The results obtained suggest that it is able to detect faulty phases as well as classify faults within quarter-cycle from the inception of fault with impeccable accuracy. Besides, as modern digital relays have been already equipped with phasor computation facility, phasor-based technique can be easily incorporated with relative ease. At last, a comparative evaluation suggests its superiority in terms of fault classification accuracy, fault detection time, diversify fault scenarios and computational requirement among other existing techniques.

scholarly journals Binary Amplitude Reflection Gratings for X-ray Shearing and Hartmann Wavefront Sensors

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 536
Author(s):  
Kenneth A. Goldberg ◽  
Antoine Wojdyla ◽  
Diane Bryant
Keyword(s):  
Operating Conditions ◽  
Design Parameters ◽  
Wavefront Aberration ◽  
Light Sources ◽  
Wavefront Sensors ◽  
X Ray ◽  
New Class ◽  
Coherent Wave ◽  
Reflection Gratings ◽  
Dynamic Operating

New, high-coherent-flux X-ray beamlines at synchrotron and free-electron laser light sources rely on wavefront sensors to achieve and maintain optimal alignment under dynamic operating conditions. This includes feedback to adaptive X-ray optics. We describe the design and modeling of a new class of binary-amplitude reflective gratings for shearing interferometry and Hartmann wavefront sensing. Compact arrays of deeply etched gratings illuminated at glancing incidence can withstand higher power densities than transmission membranes and can be designed to operate across a broad range of photon energies with a fixed grating-to-detector distance. Coherent wave-propagation is used to study the energy bandwidth of individual elements in an array and to set the design parameters. We observe that shearing operates well over a ±10% bandwidth, while Hartmann can be extended to ±30% or more, in our configuration. We apply this methodology to the design of a wavefront sensor for a soft X-ray beamline operating from 230 eV to 1400 eV and model shearing and Hartmann tests in the presence of varying wavefront aberration types and magnitudes.

Development of X80M Line Pipe Steel for Spiral Welded Pipes With Low Temperature Toughness and Excellent Weldability

2014 ◽  
Author(s):  
Nuria Sanchez ◽  
Özlem E. Güngör ◽  
Martin Liebeherr ◽  
Nenad Ilić
Keyword(s):  
Low Temperature ◽  
Life Cycle Cost ◽  
Volume Fraction ◽  
Large Diameter ◽  
Pipe Production ◽  
Strain Accumulation ◽  
Long Distance ◽  
Line Pipe ◽  
Low Temperature Toughness ◽  
Welded Pipe

The unique combination of high strength and low temperature toughness on heavy wall thickness coils allows higher operating pressures in large diameter spiral welded pipes and could represent a 10% reduction in life cycle cost on long distance gas pipe lines. One of the current processing routes for these high thickness grades is the thermo-mechanical controlled processing (TMCP) route, which critically depends on the austenite conditioning during hot forming at specific temperature in relation to the aimed metallurgical mechanisms (recrystallization, strain accumulation, phase transformation). Detailed mechanical and microstructural characterization on selected coils and pipes corresponding to the X80M grade in 24 mm thickness reveals that effective grain size and distribution together with the through thickness gradient are key parameters to control in order to ensure the adequate toughness of the material. Studies on the softening behavior revealed that the grain coarsening in the mid-thickness is related to a decrease of strain accumulation during hot rolling. It was also observed a toughness detrimental effect with the increment of the volume fraction of M/A (martensite/retained austenite) in the middle thickness of the coils, related to the cooling practice. Finally, submerged arc weldability for spiral welded pipe manufacturing was evaluated on coil skelp in 24 mm thickness. The investigations revealed the suitability of the material for spiral welded pipe production, preserving the tensile properties and maintaining acceptable toughness values in the heat-affected zone. The present study revealed that the adequate chemical alloying selection and processing control provide enhanced low temperature toughness on pipes with excellent weldability formed from hot rolled coils X80 grade in 24 mm thickness produced at ArcelorMittal Bremen.

Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

2009 ◽  
Author(s):  
Irene Garcia Garcia ◽  
Radoslav Stefanovic
Keyword(s):  
Heat Treatment ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Operational Experience ◽  
Element Analysis ◽  
Critical Crack ◽  
Circumferential Welds ◽  
Fea Model ◽  
Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

Impact of Operating Conditions and Design Parameters on Gas Turbine Hot Section Creep Life

2010 ◽  
Author(s):  
S. Eshati ◽  
M. F. Abdul Ghafir ◽  
P. Laskaridis ◽  
Y. G. Li
Keyword(s):  
Gas Turbines ◽  
Performance Model ◽  
Operating Conditions ◽  
Creep Model ◽  
Design Parameters ◽  
Gas Temperature ◽  
Creep Life ◽  
Cooling Effectiveness ◽  
Radial Temperature ◽  
The Impact

This paper investigates the relationship between design parameters and creep life consumption of stationary gas turbines using a physics based life model. A representative thermodynamic performance model is used to simulate engine performance. The output from the performance model is used as an input to the physics based model. The model consists of blade sizing model which sizes the HPT blade using the constant nozzle method, mechanical stress model which performs the stress analysis, thermal model which performs thermal analysis by considering the radial distribution of gas temperature, and creep model which using the Larson-miller parameter to calculate the lowest blade creep life. The effect of different parameters including radial temperature distortion factor (RTDF), material properties, cooling effectiveness and turbine entry temperatures (TET) is investigated. The results show that different design parameter combined with a change in operating conditions can significantly affect the creep life of the HPT blade and the location along the span of the blade where the failure could occur. Using lower RTDF the lowest creep life is located at the lower section of the span, whereas at higher RTDF the lowest creep life is located at the upper side of the span. It also shows that at different cooling effectiveness and TET for both materials the lowest blade creep life is located between the mid and the tip of the span. The physics based model was found to be simple and useful tool to investigate the impact of the above parameters on creep life.

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