Inline Inspection of Dents and Corrosion Using “High Quality” Multi-Purpose Smart-Pig Inspection Data

A new generation of geometry sensor for ILI tools has been developed. This sensor provides highly accurate geometry data of the internal pipe contour. The technology uses the benefits of a touchless distance measurement in combination with the advantages of a mechanical caliper arm. The complementary interaction allow the measurement of accurate data under demanding operational conditions. The geometry sensor technology can be combined with a navigation unit and the high resolution MFL inspection technology on so called multi-purpose ILI-tools. The merging of different inspection tasks on a single tool is an economic solution to create and add to an ILI-database for integrity management. Field experience with this new technology will be discussed, based on more than 500 miles inspected pipeline. Most inspections were performed in the US and Canada. The operational performance of the sensors justified the new design.

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

A First Step Towards the Development of a Pipeline Wrinkle Material Ultimate Limit State

While the formation of a wrinkle in an onshore pipeline is an undesirable event, in many instances this event does not have immediate pipeline integrity implications. The magnitude or severity of a wrinkle formed due to displacement controlled loading processes (e.g. slope movement, fault displacement, frost heave and thaw settlement) may increase with time, eventually causing serviceability concerns (e.g. fluid flow or inspection restrictions). Pipe wall damage leading to cracking and eventually a loss of containment involves contributions from the wrinkle formation and growth processes, as well as, wrinkle deformations promoted by in-service line pressure, temperature and seasonal soil displacements. The objective of this paper is to provide an overview of the ongoing research efforts, sponsored by TransCanada PipeLines Ltd. and Tokyo Gas Co. Ltd., towards the development of a mechanics based wrinkle ultimate limits state that may be used in future to evaluate the long term integrity of wrinkled pipeline segments. The research efforts include non-linear finite element modeling to demonstrate the ability of experimentally derived material properties to predict the formation of through wall cracking induced by high and low frequency load effects. This paper outlines the material testing program used to support the development of failure criteria capable of considering the contributions of monotonic deformation, as well as, high and low cycle cyclic loading.

Probabilistic Assessment of Minor Mechanical Damage

In-line inspection (ILI) of the Trans Alaska Pipeline System (TAPS) using high resolution metal loss tools indicated 77 locations with suspected minor mechanical damage features (MDF). The tools used are able to detect the presence of a suspected feature, and measure indented dimensions, but are insufficient to detect the presence of cracks or gouges needed to reliably assess feature severity based solely on the ILI data. Excavations of 42 sites deemed most severe provided important field data characterizing residual deformation dimensions, the occurrence of gouges or cracks, and allowing a reliable field assessment of defect severity. Upon completion of the excavations, 35 possible MDF locations remained unexcavated. An engineering evaluation was undertaken to assess whether or not these remaining minor MDF pose a threat that is significant enough to warrant excavation. Multiple assessment methods were utilized including deterministic, probabilistic, and risk assessment methods. The probabilistic assessment of 35 unexcavated MDFs was performed using PCFStat; or Pressure Cycle Fatigue Statistical Assessment, which uses Monte Carlo simulation to estimate remaining fatigue life. PCFStat performs 1,000’s of simulations for each case where the input parameters are randomly selected from expected distributions. Of particular importance is the fatigue environment of the location. The results of the probabilistic assessment were used to estimate the potential for failure of remaining MDFs. The results suggest that 25 of 35 unexpected damage features had a POF of less than 10−4 over the remaining expected pipeline life cycle and thus are unlikely to fail. Alyeska considered a combination of probabilistic, deterministic and risk assessment results to decide on the actual locations to be examined. The results of probabilistic analysis also were found to support the outcome of the operator’s risk-based evaluation process.

Nonlinear Harmonic Monitoring of Gouged Dents in Pipeline Specimens Under Cyclic Loading

The only in-line inspection technology commercially available for quantitative evaluation of gouged dents is the geometry pig which cannot discriminate between gouged and smooth dents and has no sensitivity to re-rounded dents. Southwest Research Institute® (SwRI®), has been funded by the US Pipeline and Hazardous Materials Safety Administration (PHMSA) and the Gas Research Institute (GRI) through the Pipeline Research Council International (PRCI), to determine the capability of the nonlinear harmonic (NLH) method to characterize the severity of gouged dents, including those that have been re-rounded by internal pressure. This paper describes the NLH method and presents a summary of results from previous work involving burst tests of gouged dents in 24” pipe as a precursor to the current work that involves experiments with four pressure chambers made from 12-inch line pipe under cyclic pressure changes. In each case, internal scanner hardware, driven from outside the pipe, deployed NLH probes against the pipe inner surface, the gouges being on the outer surface. Analysis of the mapped NLH signals on the inner pipe surface revealed residual strain patterns in the pipe and the strain anomalies produced by gouging. The strain anomalies clearly indicated the presence of the gouges on the outside surface, even when they had re-rounded. The signal maps also indicated the length and width of the gouges whereas the signal strength indicated the residual depth. Data are presented showing that the NLH method is capable of ranking the severity of pipeline gouged dents and their propensity for failure under cyclic loading.

SCC Management and Integrity Planning in a Gas Pipeline

Stress Corrosion Cracking (SCC) is a major integrity management concern for many gas and oil pipeline operators. Predictive models for Stress Corrosion Crack growth were developed using laboratory test data from the mid 1970’s, and limited inspection data and excavation measurements from the early 1990’s. Extensive efforts continue to be made to develop strategies for a better management of the SCC problem. In this paper, a study of crack growth rates was conducted on the Williams 16-inch gas pipeline using data from two consecutive in-line crack detection tool runs and direct field measurements. Findings from this study provide a direct measurement of crack growth rates for ILI crack features with depths ranging from 12.5%wt to 40%wt. Future integrity of the pipeline was assessed. The integrity management strategies could be further refined using the calculated crack growth rate, field excavation data and fracture mechanics based API 579 FAD approach.

An External Corrosion Direct Assessment Module for a Pipeline Integrity Management System

A significant part of the high pressure gas transport system of Gasunie cannot be examined by in-line inspection techniques. To ensure safe operation of these pipelines, an External Corrosion Direct Assessment (ECDA) module for PIMSLIDER (a pipeline integrity management system) is currently under development. The functional specifications of this module are based on NACE RP0502-2002, a recommended practice for ECDA. In addition to this, a new probabilistic methodology has been adopted, to take account for uncertainties associated with ECDA and to quantify the contributions from aboveground surveys and excavations to the integrity of a pipeline. This methodology, which is based on Structural Reliability Analysis (SRA) and Bayesian updating techniques, is presented in more detail in paper IPC2006-10092 of this conference. The DA module of PIMSLIDER enables computerized storage, retrieval and processing of all appropriate pipeline data and therefore guarantees highly accurate, reproducible and time saving integrity analyses of the Gasunie grid. Another important function of this system is the ability to use the complete database of all pipelines to pre-assess the integrity of a particular pipeline. This automated retrieval of data from pipelines with similar characteristics and/or environmental conditions results in a substantial increase of accessible data and enables Gasunie to improve the reliability of applied statistics throughout the process. As a consequence, the overall cost of inspections and excavations can be greatly reduced. In the Pre-Assessment phase, the DA module assists the integrity manager in gathering and analyzing data necessary to determine the current condition of a pipeline. After collection and visualization of the available data, the user can identify suitable ECDA regions. Furthermore, the gathered data are used to construct prior distributions of parameters relevant to the SRA model, such as the number and size of corrosion defects and pipeline-related parameters. In the Indirect Inspections step, the DA module allows the user to store and analyze the data from aboveground surveys, in order to identify and define the severity of coating faults and areas at which corrosion activity may occur. The probabilistic methodology accounts for the individual performance of each applied survey technique in terms of missed defects and false indications, in general a major source of uncertainty in ECDA. In the Direct Examinations phase, excavations are carried out to collect data to assess possible corrosion activity. Subsequently, the ECDA module uses this information to update, among other things, the parameters concerning the performance of survey techniques, the number of defects and the corrosion rate. As a result, updated failure frequencies are calculated for each ECDA-region (after each excavation if required), which are then used by the DA module to advise the integrity manager if additional mitigating activities are necessary, or by defining a reassessment interval.

Modeling the Interactions of Hydrogen, Stress and Dissolution in Near-Neutral pH Stress Corrosion Cracking of Pipelines

A thermodynamic model was developed to determine the interactions of hydrogen, stress and anodic dissolution at the crack-tip during near-neutral pH stress corrosion cracking in pipelines. By analyzing the free-energy of the steel in the presence and absence of hydrogen and stress, it is demonstrated that a synergism of hydrogen and stress promotes the cracking of the steel. The enhanced hydrogen concentration in the stressed steel significantly accelerates the crack growth. The quantitative prediction of the crack growth rate in near-neutral pH environment is based on the determination of the effect of hydrogen on the anodic dissolution rate in the absence of stress, the effect of stress on the anodic dissolution rate in the absence of hydrogen, the synergistic effect of hydrogen and stress on the anodic dissolution rate at the crack-tip and the effect of the variation of hydrogen concentration on the anodic dissolution rate.

A Statistical Predictive Model to Prioritize Site Selection for Stress Corrosion Cracking Direct Assessment

Pipeline stress-corrosion cracking (SCC) is an ongoing integrity concern for pipeline operators. A number of different strategies are currently employed to locate and mitigate SCC. Ultrasonic in-line inspection tools have proven capable of locating SCC, but reliability of these tools in gas pipelines remains in question. Rotating hydrotest programs are effectively employed by some companies but may not provide useful information as to the location of SCC along the pipeline. NACE Standard RP0204-2004 (SCC Direct Assessment Methodology) outlines factors to consider and methodologies to employ to predict where SCC is likely to occur, but even this document acknowledges that there are no well-established methods for predicting the presence of SCC with a high degree of certainty. Predictive modelling attempts to date have focused on establishing quantitative relationships between environmental factors and SCC formation and growth; these models have achieved varying degrees of success. A statistical approach to SCC predictive modelling has been developed. In contrast to previous models that attempted to determine direct correlations between environmental parameters and SCC, the new model statistically analyzed data from dig sites where SCC was and was not found. Regression techniques were used to create a multi-variable logistic regression model. The model was applied to the entire pipeline and verification digs were performed. The dig results indicated that the model was able to predict locations of SCC along the pipeline.

Direct Assessment (DA) White Paper

The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) has drafted a direct assessment (DA) white paper to summarize the current state of direct assessment activities and practice. Several industry organizations, associations and operating companies have subsequently added content to this white paper improving the accuracy and updating the current state of direct assessment in the pipeline industry. This white paper includes information on DA standards development, drivers, current efforts to further develop DA and an overview of the path forward. Several recent high profile pipeline failures drove the public expectation that pipeline operators understand and improve the integrity of their pipelines. PHMSA has promulgated regulations to require this improved understanding and management of pipeline integrity. During the preparation of the new integrity management requirements, it was recognized that some gas transmission pipelines could not be inspected using then-available assessment techniques, pressure testing and in-line inspection. As a result, PHMSA along with the industry developed and codified several processes for assessing these lines. These processes, which utilized proven tools as part of assessment processes, are collectively called DA.