J Predictions for Defective Pipe Elbows via the Reference Stress Method

In R6, the J-based failure assessment diagram (FAD) method is used in the fracture assessment, and is underpinned by the reference stress J scheme. Therefore, an assessment using the R6 FAD method is equivalent to a J prediction using the reference stress method. In this paper, the effect of global and local limit load solutions for defective elbows on the reference stress and hence the J predictions is investigated using published three dimensional elastic-plastic finite element (FE) J results, in order to create guidance for users to follow when performing structural integrity assessments of defective elbows using the R6 procedure. The results show that using the global limit load solutions recommended in this paper can lead to good and reasonably conservative J predictions. However, the availability of global limit load solutions is very limited. The results also show that using the local limit load evaluated from the local limit load model recommended in this paper can lead to conservative J predictions for most of the cases considered.

Evaluating the Probability of Detection Capability of Permanently Installed Sensors Using a Structural Integrity Informed Approach

There is a growing interest in using permanently installed sensors to monitor for defects in engineering components; the ability to collect real-time measurements is valuable when evaluating the structural integrity of the monitored component. However, a challenge in evaluating the detection capabilities of a permanently installed sensor arises from its fixed location and finite field-of-view, combined with the uncertainty in damage location. A probabilistic framework for evaluating the detection capabilities of a permanently installed sensor is thus proposed. By combining the spatial maps of sensor sensitivity obtained from model-assisted methods and probability of defect location obtained from structural mechanics, the expectation and confidence in the probability of detection (POD) can be estimated. The framework is demonstrated with four sensor-component combinations, and the results show the ability of the framework to characterise the detection capability of permanently installed sensors and quantify its performance with metrics such as the $${\mathrm{a}}_{90|95}$$ a 90 | 95 value (the defect size where there is 95% confidence of obtaining at least 90% POD), which is valuable for structural integrity assessments as a metric for the largest defect that may be present and undetected. The framework is thus valuable for optimising and qualifying monitoring system designs in real-life engineering applications.

Engineering Criticality Assessments of Floating Offshore Platforms Based on Time Domain Structural Response Analysis

This paper presents a time-domain S-N fatigue analysis and an approach to reliable and robust engineering criticality assessments to supplement or provide an alternative to S-N fatigue assessments of offshore platform structures based on time domain structural response analysis. It also provides recommendations for industry standards to improve guidance for structural integrity assessments of offshore platforms using fracture mechanics. Demand continues to grow in the offshore industry to attain value from captured operational data for a number of purposes, including the reduction of uncertainties in structural integrity assessments during design and over the operational lifetime of floating offshore platforms. Recent advances in time domain structural analysis technology demonstrate substantially more accurate assessments of non-linear platform loadings and responses with enhanced computational efficiency. The current S-N approach for fatigue design and integrity assessments calculates a fatigue damage factor that does not address how loading occurs over time (ABS, DNVGL-RP-C203). For the present study, engineering criticality assessments (ECAs) based on fracture mechanics theory (BS 7910) are applied utilizing time-domain loading information theory. The ECA returns the smallest initial flaws that can grow to a critical size during a design lifetime, which can serve as an indicator of acceptability during design, a technical basis for in-service inspection intervals and facilitates asset integrity and life extension assessments. Critical initial flaws are calculated using the Paris Law (BS 7910) and cumulative fatigue crack growth in two ways: with and without an integrated and consistent check for fracture instability. The results are compared with those from S-N fatigue analyses and recommendations are provided.

Verification of Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessel

Nowadays, it has been recognized that probabilistic fracture mechanics (PFM) is a promising methodology in structural integrity assessments of aged pressure boundary components of nuclear power plants, because it can rationally represent the influencing parameters in their inherent probabilistic distributions without over conservativeness. A PFM analysis code PFM analysis of structural components in aging light water reactor (PASCAL) has been developed by the Japan Atomic Energy Agency to evaluate the through-wall cracking frequencies of domestic reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) transients. In addition, efforts have been made to strengthen the applicability of PASCAL to structural integrity assessments of domestic RPVs against nonductile fracture. A series of activities has been performed to verify the applicability of PASCAL. As a part of the verification activities, a working group was established with seven organizations from industry, universities, and institutes voluntarily participating as members. Through one-year activities, the applicability of PASCAL for structural integrity assessments of domestic RPVs was confirmed with great confidence. This paper presents the details of the verification activities of the working group, including the verification plan, approaches, and results.

Application of Probabilistic Fracture Mechanics to Reactor Pressure Vessel Using PASCAL4 Code

Probabilistic fracture mechanics (PFM) is considered to be a promising methodology in structural integrity assessments of pressure-boundary components in nuclear power plants since it can rationally represent the inherent probabilistic distributions for influence parameters without over-conservativeness. To strengthen the applicability of PFM methodology in Japan, Japan Atomic Energy Agency has developed a PFM analysis code PASCAL4 which enables the failure frequency evaluation of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and thermal transients. PASCAL4 is expected to make a significant contribution to the probabilistic integrity assessment of Japanese RPVs. In this study, PFM analysis for a Japanese model RPV in a pressurized water reactor (PWR) was conducted using PASCAL4, and the effects of nondestructive examination (NDE) and neutron flux reduction on failure frequencies of the RPV were quantitatively evaluated. From the analysis results, it is concluded that PASCAL4 is useful for probabilistic integrity assessments of embrittled RPVs and can enhance the applicability of PFM methodology.

Qualitative and Semi-Quantitative Model for Estimating the Probability of Failure at River Crossings

Pipeline river crossings are typically managed by using a combination of flood monitoring, ground inspections, integrity assessments, and remediations. Using a probabilistic model to assess the likelihood of failure at river crossings would enable combined consideration of all factors that contribute to the failure threat, provide site rankings to support discrete mitigation prioritizations, allow for evaluation of whether a crossing is acceptable in regard to a risk target, and provide a “check” to the deterministic integrity management methods. This paper describes two models for estimating the pipeline probability of failure at river crossings. The first model is a qualitative scoring model that can be easily implemented by operators and consultants. This model employs a weighting-factors approach to consider the multiple variables that contribute to pipeline exposures and overstress given exposure. The results may be applied to threat rank diverse crossings, as well estimate the probability of failure at a crossing relative to that at historical failure sites. The second model is a semi-quantitative model that 1) estimates the likelihood of a crossing exposure occurring, 2) estimates the associated scour length, 3) assesses the pipelines critical span length, and 4) quantifies the probability that a span length longer than the critical span length could form. This model may be applied to achieve the same goals as the qualitative model, and also compare the probability of failure at a river crossing to a reliability target. Due to the complexity of this model and the paper length limits, it is conceptually described within this paper. The results demonstrated that the model output site rankings correlated reasonably with those estimated by pipeline integrity program managers, the scour depth and length prediction results were consistent with measured historical scours, and the pipeline probability of failure at the assessed river crossings were within expected ranges.

TunnelCAM- A HDR Spherical Camera Array for Structural Integrity Assessments of Dam Interiors

The United States of America has an estimate of 84,000 dams of which approximately 15,500 are rated as high-risk as of 2016. Recurrent geological and structural health changes require dam assets to be subject to continuous structural monitoring, assessment and restoration. The objective of the developed system is targeted at evaluating the feasibility for standardization in remote, digital inspections of the outflow works of such assets to replace human visual inspections. This work proposes both a mobile inspection platform and an image processing pipeline to reconstruct 3D models of the outflow tunnel and gates of dams for structural defect identification. We begin by presenting the imaging system with consideration to lighting conditions and acquisition strategies. We then propose and formulate global optimization constraints that optimize system poses and geometric estimates of the environment. Following that, we present a RANSAC frame-work that fits geometric cylinder primitives for texture projection and geometric deviation, as well as an interactive annotation frame-work for 3D anomaly marking. Results of the system and processing are demonstrated at the Blue Mountain Dam, Arkansas and the F.E. Walter Dam, Pennsylvania.