Risk Based Inspection Planning for Fatigue Damage in Offshore Steel Structures

2015 ◽  
Author(s):  
Tom Lassen ◽  
Naman Recho
Keyword(s):  
Crack Propagation ◽  
Crack Detection ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Life Extension ◽  
Inspection Time ◽  
Reliable Estimate ◽  
Practical Case ◽  
Fatigue Reliability ◽  
Inspection Planning

High fatigue reliability is one of the most important design criteria for welded offshore steel structures. Due to repeated wave loading fatigue cracks may initiate and grow in welded joints that are important for the integrity of these structures. The present paper presents the methodology and the practical calculations for risk based inspection planning for fatigue cracks in welded details. Due to the uncertainty in the variables involved in the problem the planning has to be carried out by stochastic modeling and risk based assessments. Scatter in potential crack growth has to be analyzed by applied probabilistic facture mechanics and the uncertainty in the performance of the actual inspection technique has to be determined. With given risk acceptance criteria the practical outcome of the analyses is recommended inspection techniques and associated planned inspection time intervals. The classical theory is outlined and the latest recommendations from a Joint Industry Project recently completed by Det Norske Veritas in Norway are discussed. Discussion on how to model the fatigue process correctly is emphasized, particularly the role of time to crack initiation versus the subsequent crack propagation phase. Proper modeling of these two phases is crucial to get the potential crack path correct and thus obtain a reliable estimate of the probability of crack detection. For the crack propagation phase the selection of geometry functions is addressed. A practical case study for life extension of an offshore oil loading system is finally presented. A structural significant item in the system is the steel gooseneck connection for the sub-sea flexible loading hoses. The case is an interesting one in the way that two similar systems were analyzed independently, one analysis based on the tradition S-N approach and one where the decisions were reliability based by applying the Risk Based Inspection approach.

scholarly journals Pixel-Level Fatigue Crack Segmentation in Large-Scale Images of Steel Structures Using an Encoder–Decoder Network

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4135
Author(s):  
Chuanzhi Dong ◽  
Liangding Li ◽  
Jin Yan ◽  
Zhiming Zhang ◽  
Hong Pan ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Large Scale ◽  
Crack Detection ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Life Cycles ◽  
Detection Methods ◽  
Destructive Testing ◽  
Existing Structures ◽  
Fatigue Crack Detection

Fatigue cracks are critical types of damage in steel structures due to repeated loads and distortion effects. Fatigue crack growth may lead to further structural failure and even induce collapse. Efficient and timely fatigue crack detection and segmentation can support condition assessment, asset maintenance, and management of existing structures and prevent the early permit post and improve life cycles. In current research and engineering practices, visual inspection is the most widely implemented approach for fatigue crack inspection. However, the inspection accuracy of this method highly relies on the subjective judgment of the inspectors. Furthermore, it needs large amounts of cost, time, and labor force. Non-destructive testing methods can provide accurate detection results, but the cost is very high. To overcome the limitations of current fatigue crack detection methods, this study presents a pixel-level fatigue crack segmentation framework for large-scale images with complicated backgrounds taken from steel structures by using an encoder-decoder network, which is modified from the U-net structure. To effectively train and test the images with large resolutions such as 4928 × 3264 pixels or larger, the large images were cropped into small images for training and testing. The final segmentation results of the original images are obtained by assembling the segment results in the small images. Additionally, image post-processing including opening and closing operations were implemented to reduce the noises in the segmentation maps. The proposed method achieved an acceptable accuracy of automatic fatigue crack segmentation in terms of average intersection over union (mIOU). A comparative study with an FCN model that implements ResNet34 as backbone indicates that the proposed method using U-net could give better fatigue crack segmentation performance with fewer training epochs and simpler model structure. Furthermore, this study also provides helpful considerations and recommendations for researchers and practitioners in civil infrastructure engineering to apply image-based fatigue crack detection.

Analytical Study of Fatigue-crack Propagation on Web-Gap Plate

2017 ◽  
Author(s):  
Ryo Tobita ◽  
Hirohisa Suzuki
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Analytical Study ◽  
Fatigue Cracks ◽  
Crack Problem ◽  
Steel Structures ◽  
Structural Repair ◽  
Girder Bridges ◽  
Girder Bridge

The study describes behaviour of fatigue-cracks for evaluation of structural repair priority. Around 65% of the total length of the Metropolitan Expressway in Japan is composed of viaducts made of steel. And fatigue crack problem has been occurred on the steel structures. In particular, around 30% of all the fatigue-cracks occurred at “Web-Gap Plate(WGP)” which is attached in plate girder bridges. This study focused on the fact that those cracks do not always induce collapse of the girder bridge immediately, even though the number of cracks, which are needed to repair, is becoming increasing. As a result of the study, repair priorities of around 60% cracks on WGP can be lowered by analysing maintenance data accumulated since 2001.

Efficient Planning

2017 ◽  
pp. 328-349
Author(s):  
N. A. Nechval ◽  
K. N. Nechval
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Load Cycle ◽  
Fatigue Reliability ◽  
Inspection Planning ◽  
Lifetime Distributions ◽  
Inspection Strategy ◽  
Efficient Planning ◽  
Periodic Inspections ◽  
Service Inspection

The main aim of this chapter is to present more accurate stochastic fatigue models for solving the fatigue reliability problems, which are attractively simple and easy to apply in practice for situations where it is difficult to quantify the costs associated with inspections and undetected cracks. From an engineering standpoint the fatigue life of a structure consists of two periods: (i) crack initiation period, which starts with the first load cycle and ends when a technically detectable crack is presented, and (ii) crack propagation period, which starts with a technically detectable crack and ends when the remaining cross section can no longer withstand the loads applied and fails statically. Periodic inspections of aircraft, which are common practice in order to maintain their reliability above a desired minimum level, are based on the conditional reliability of the fatigued structure. During the period of crack initiation, when the parameters of the underlying lifetime distributions are not assumed to be known, for efficient in-service inspection planning (with decreasing intervals as alternative to constant intervals often used in practice for convenience in operation), the pivotal quantity averaging (PQA) approach is offered. During the period of crack propagation (when the damage tolerance situation is used), the approach, based on an innovative crack growth equation, to efficient in-service inspection planning (with decreasing intervals between sequential inspections) is proposed to construct more accurate reliability-based inspection strategy in this case. To illustrate the suggested approaches, numerical examples are given.

Mechanoluminescent Testing as an Efficient Inspection Technique for the Management of Infrastructures

2017 ◽  
Vol 12 (3) ◽  
pp. 506-514 ◽  
Author(s):  
Akihito Yoshida ◽  
◽  
Linsheng Liu ◽  
Dong Tu ◽  
Shigenobu Kainuma ◽  
...  
Keyword(s):  
Crack Detection ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Field Testing ◽  
Box Girders ◽  
Inspection Method ◽  
Steel Members ◽  
Precautionary Measures ◽  
Corrosion Protection Coating ◽  
Protection Coating

This paper reports on the mechanoluminescence inspection technology we have developed and its applications. The inspection technology is expected to identify deterioration and damage, such as fatigue cracks developed on steel members of steel structures, using particular mechanoluminescence (ML) phenomenon. In field testing at an urban highway bridge currently in service, fatigue cracks in steel box girders were successfully detected using the proposed technology. In addition, using a conventional crack detection method known as magnetic particle inspection (MT), similar results were obtained in terms of crack judgment, suggesting that the reliability of the ML method is equivalent to that of the MT method. An advantage of the ML inspection method is that it does not require removing corrosion protection coating, saving labor that is necessary in the MT method. The field testing also examined the possibility of evaluating precautionary measures (repair) as another application of the ML technique. As a result, the ML technique quantitatively evaluated that detected cracking had been properly repaired (removed). It is expected that the ML technique will contribute to effective maintenance and management of infrastructures from the perspective of preventive maintenance.

Simulation of Behavior of Fatigue Cracks: A Complete Industrial Process on a Typical Connection in a FPSO

2009 ◽  
Author(s):  
Michelle Serror ◽  
Nicolas Marchal
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Interaction Analysis ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Inspection Planning ◽  
Local Approach ◽  
Joint Research ◽  
Welded Structure ◽  
Joint Research Project

To assess FPSO condition, it is necessary to adjust the inspection process and the inspection planning in accordance with the safety target. Crack propagation may be a leading criterion for designing inspection planning and repair planning. In order to realistically anticipate the possible propagation of either cracks not detected during inspection or cracks initiated after this inspection, a joint research project between three French companies (Nexter Systems, CETIM, and Bureau Veritas) has been carried out to obtain improved approach. This approach involves various steps of fatigue crack behavior leading to failure. This paper presents a part of this research dedicated to the development of tools applicable to FPSO structural assessment. This method takes into account the analysis of simultaneous crack propagation. It involves interaction between these cracks. This technique avoids successive re-meshing all along the crack path. Multi-crack initiations are calculated using a multi-axial fatigue damage criterion based on a local approach. A Line Spring Method coupled with a fitted structural stiffness condensation method is used to calculate the stress intensity factors, with a view to determine the crack propagation rate. This method allows monitoring the redistribution of the stresses generated by crack opening. This approach has been then validated on a welded mock-up, which was designed to provide several crack locations in different zones of the structure. An extended instrumentation of this welded structure has allowed tests to check accurately crack initiations and to follow crack propagation. The results are in good agreement with calculation predictions. This approach is now used to assess fatigue crack propagation in a FPSO. An example is provided on a welded connection between bracket and longitudinal stiffener, on the transverse bulkhead where a propagation of four cracks has been followed. This analysis shows an important gain in the fatigue life span prediction versus current fracture mechanics analysis. This gain is mainly due to a better interaction analysis between local cracked area and global structural behavior.

Fatigue crack detection method using analysis of vibration signal

2017 ◽  
Vol 1 (20) ◽  
pp. 63-74 ◽  
Author(s):  
Arkadiusz Rychlik ◽  
Krzysztof Ligier
Keyword(s):  
Crack Detection ◽  
Fatigue Cracks ◽  
Fatigue Cracking ◽  
Vibration Signal ◽  
Technical Condition ◽  
Visual Methods ◽  
Signal Characteristics ◽  
Fatigue Crack Detection ◽  
Sample Structure ◽  
Change Identification

This paper discusses the method used to identify the process involving fatigue cracking of samples on the basis of selected vibration signal characteristics. Acceleration of vibrations has been chosen as a diagnostic signal in the analysis of sample cross section. Signal characteristics in form of change in vibration amplitudes and corresponding changes in FFT spectrum have been indicated for the acceleration. The tests were performed on a designed setup, where destruction process was caused by the force of inertia of the sample. Based on the conducted tests, it was found that the demonstrated sample structure change identification method may be applied to identify the technical condition of the structure in the aspect of loss of its continuity and its properties (e.g.: mechanical and fatigue cracks). The vibration analysis results have been verified by penetration and visual methods, using a scanning electron microscope.

Methodology to Develop Fitness-for-Service Assessments for Crack Detection In-Line Inspection Data

2006 ◽  
Author(s):  
David Shanks ◽  
Rob Leeson ◽  
Corina Blaga ◽  
Rafael G. Mora
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Crack Detection ◽  
Corrosion Cracking ◽  
Life Extension ◽  
Remaining Life ◽  
Service Monitoring ◽  
Criticality Assessment ◽  
Inspection Data

Implementation of Integrity Management Programs (IMP) for pipelines has motivated the design of Fitness-For-Service methodologies to assess Stress Corrosion Cracking (SCC) and fatigue-dependent features reported by Ultrasonic Crack Detection (UTCD) In-Line Inspections. The philosophical approach defined by the API 579 [1] “Fitness-For-Service” from the petrochemical industry in conjunction with Risk-based standards and regulations (i.e. CSA-Z662-2003 [2] and US DOT 49 Parts 192 [3] and 195 [4]) and in-line inspection validation (i.e. API 1163 [5]) approaches from the pipeline industry have provided the engineering basis for ensuring the safety, reliability and continued service of the in-line inspected pipelines. This paper provides a methodology to develop short and long-term excavation and re-inspection programs through a four (4) phase-process: Pre-Assessment, Integrity Criticality Assessment, Remediation and Repair, Remaining Life Extension and In-Service Monitoring. In the first phase, Pre-assessment, areas susceptible to Stress Corrosion Cracking (SCC) and fatigue-dependent features are correlated to in-line inspection data, soil modeling, pipeline and operating conditions, and associated consequences in order to provide a risk-based prioritization of pipeline segments and technical understanding for performing the assessment. The second phase, Integrity Criticality Assessment, will develop a short-term maintenance program based on the remaining strength of the in-line inspection reported features previously correlated, overlaid and risk-ranked. In addition, sites may be identified in Phase 1 for further investigation. In the third phase, a Remediation and Repair program will undertake the field investigation in order to repair and mitigate the potential threats as well as validating the in-line inspection results and characterization made during the Pre-assessment and Integrity Criticality Assessment (Phases 1 & 2). With the acquired knowledge from the previous three (3) phases, a Remaining Life Extension and In-Service Monitoring program will be developed to outline the long-term excavation and re-inspection program through the use of SCC and Fatigue crack growth probabilistic modeling and cost benefit analysis. The support of multiple Canadian and US pipeline operating companies in the development, validation and implementation of this methodology made this contribution possible.

scholarly journals Fatigue Crack Growth Behaviour and Role of Roughness-Induced Crack Closure in CP Ti: Stress Amplitude Dependence

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1656
Author(s):  
Mansur Ahmed ◽  
Md. Saiful Islam ◽  
Shuo Yin ◽  
Richard Coull ◽  
Dariusz Rozumek
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Closure ◽  
Fatigue Cracks ◽  
Propagation Mechanism ◽  
Amplitude Dependence ◽  
Crack Growth Behaviour ◽  
Crack Propagation Mechanism ◽  
Cp Ti

This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. Crack deflection and crack branching that cause roughness-induced crack closure (RICC) appeared at all studied stress amplitudes; hence, RICC at various stages of crack propagation (100, 300 and 500 µm) could be quantitatively calculated. Noticeably, a lower RICC at higher stress amplitudes (227 MPa) for fatigue cracks longer than 100 µm was found than for those at 175 MPa. This caused the variation in crack growth rates in the studied conditions.

Fatigue crack propagation monitoring in steel structures with intelligent systems

2000 ◽  
pp. 117-126
Author(s):  
Muhammad S. Rahman ◽  
Toshiyuki Oshima ◽  
Shuichi Mikami ◽  
Tomoyuki Yamazaki ◽  
Naoyuki Takada
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Intelligent Systems ◽  
Steel Structures
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