Advanced Techniques for Establishing Long-Term Performance of Composite Repair Systems

Although composite materials are used to repair and reinforce a variety of anomalies in high pressure transmission gas and liquid pipelines, there continues to be widespread debate regarding what constitutes a long-term composite repair. The United States regulations require that composite repairs must be able to permanently restore the serviceability of the repaired pipeline, while in contrast the Canadian regulations take a more prescriptive approach by integrating the ASME PCC-2 and ISO 24817 composite repair standards along with a requirement for establishing a 50-year design life. In this paper the author provides a framework for what should be considered in qualifying a composite repair system for long-term performance by focusing on the critical technical aspects associated with a sound composite repair. The presentation includes a discussion on establishing an appropriate composite design stress using the existing standards, using full-scale testing to ensure that stresses in the repair do not exceed the designated composite design stresses, and guidance for operators in how to properly integrate their pipeline operating conditions to establish a design life. By implementing the recommendations presented in this paper, operators will be equipped with a resource for objectively evaluating the composite repair systems used to repair their pipeline systems.

Development and Validation of Load-Interaction Based Models for Crack Growth Prediction

This investigation primarily focused on the validation of the software being developed for crack growth and remaining life prediction using SCADA data. A total of nine pressure spectra, four for oil pipelines and five for gas pipelines, have been collected and used as inputs for the software. It was found that these spectra could be categorized as the underload-, the meanload- and the overload-dominant spectra; each of them have shown different effects on crack growth: the underload spectra, typical of pressure fluctuations at the discharging sites, are most susceptible to crack growth because of load interactions between the minor pressure fluctuations and the unload cycles; while the overload spectra, often found at the suction site, have exhibited retarded crack growth due to the retardation effects caused by overloading. The relative severity of the load interactions in terms of crack growth rate for a given spectrum was quantified using a parameter termed as the Spectrum Factor. A Spectrum Factor greater than one indicates the enhanced crack growth rate by load interactions, such as the case where unloading is frequently present in the pressure spectra, while a Spectrum Factor lower than one may be associated with a retarded crack growth, which can be seen in pressure spectra with predominant overloading events. The predictions made by the models being developed were also compared with those made by the rainflow counting method. The software allows for the SCADA/pressure fluctuation data, in excel spreadsheet format, to be directly analyzed producing a projected remaining life of the pipeline based on the past pressure fluctuations and the assumed future pressure fluctuations.

Validating ILI Accuracy Using API 1163

It is important to validate the accuracy of in-line inspection (ILI) tools to know how many excavations are needed to maintain the integrity of a pipeline segment. Performing sufficient excavations is important to ensure there are no defects left in the pipeline that have even a remote chance of failure. In some cases additional excavations may be necessary to ensure safety where in other cases no excavations may be necessary. This paper looks at using spatially recorded metal-loss data collected “in-the-ditch” to measure the accuracy of ILI tool results. Examples of spatial in-ditch data are laser scans for external corrosion and UT scans for internal corrosion. Spatially mapped metal loss, because all of the corrosion area is mapped, has the advantage of allowing more comparisons to be made for a given corrosion area and also allows the interaction among corrosion pits to be studied for examining burst pressure calculation accuracy. From our studies we find the depth error for shallow corrosion 10%–20% wt deep is often not representative of deeper corrosion in the same pipeline and the interaction criteria for ILI tools needs to be larger than the interaction criteria for in-ditch data. Examples are shown with these types of results, and by interpreting the results in conjunction with API 1163, certain ILI runs are shown that require no excavations where others may require additional excavations than suggested by normal +/−10% wt ILI data.

Implementing a Geohazard Integrity Management Program: Statistics and Lessons Learned Over 15 Years

Over the last 15 years, BGC Engineering Inc. has developed and implemented a geohazards Integrity Management Program (IMP) with 12 major pipeline operators (consisting of gas and oil pipelines and of both gathering and transmission systems). Over this time, the program has been applied to the assessment of approximately 13,500 individual hydrotechnical and geotechnical geohazard sites spanning approximately 63,000 km of operating pipelines in Canada and the USA. Hydrotechnical (watercourse) and geotechnical (slope) hazards are the primary types of geohazards that have directly contributed to pipeline failures in Canada. As with all IMPs, the core objectives of a geohazard management system are to ensure a proactive approach that is repeatable and defensible. In order to meet these objectives, the program allows for varying levels of intensity of inspection and a recommended timescale for completion of actions to manage the identified geohazards in accordance with the degree of hazard that the site poses to the pipeline. In this way, the sites are managed in a proactive manner while remaining flexible to accommodate the most current conditions at each site. This paper will provide a background to the key components of the program related specifically to existing operating pipeline systems, present pertinent statistics on the occurrence of various types of geohazards based on the large dataset of inspections, and discuss some of the lessons learned in the form of program results and program challenges from implementing a geohazard integrity management system for a dozen operators with different ages of systems, complexity of pipeline networks, and in varied geographic settings.

Development of Selective Seam Weld Corrosion Test Method

Selective seam weld corrosion (SSWC) of electric resistance welded (ERW) pipelines has been identified as a potential risk to pipeline safety. Due to recent pipeline failures, where seam weld defects may have played a significant role, the National Transportation Safety Board called upon the Pipeline and Hazardous Materials Safety Administration (PHMSA) to conduct a comprehensive study to identify actions that can be used by operators to eliminate catastrophic longitudinal seam failures in pipelines. Battelle contracted Kiefner and Associates, Inc. and Det Norse Veritas (U.S.A.) Inc. (DNV GL) with the objective to assist PHMSA in addressing this issue. The objective of one of the tasks performed by DNV GL was to develop a reliable, rapid, non-destructive, field-deployable test method that can quantify SSWC susceptibility on operating pipelines containing ERW seams. For this effort, two different, field deployable, non-destructive methods were evaluated in laboratory testing. The methods were validated using a standard destructive test for assessing SSWC susceptibility. One method was based on measurement of the local potential difference between the seam weld and the adjacent base metal while the second was based on differences in the corrosion kinetics between the seam weld and the base metal. The method that is based on corrosion kinetics was found to be most effective in identifying SSWC susceptible pipe steels. It utilizes a barnacle cell to conduct linear polarization resistance measurements on small, selected areas of the pipe (e.g., the weldment or base metal). Additional laboratory as well as field-testing is planned to further validate the test method.

Advancements in the Detection and Sizing of “Pinhole” Metal Loss

At IPC 2010 PII Pipeline Solutions (PII) presented the paper “VALIDATION OF LATEST GENERATION MFL IN-LINE INSPECTION TECHNOLOGY LEADS TO IMPROVED DETECTION AND SIZING SPECIFICATION FOR PINHOLES, PITTING, AXIAL GROOVING AND AXIAL SLOTTING”1, IPC 2010-31124. The suggestion was that this improvement would allow operators to make more informed pipeline integrity decisions in future. In the 4 years since this paper was presented many hundreds of runs have been completed with this latest generation MFL ILI technology, capturing information on tens of thousands of kilometers of pipe, and generating a significant volume of dig verification data. In collaboration with Oil & Gas pipeline operators around the world this growing dig verification database has been utilized to improve software models, algorithms, & analysis processes to validate and further enhance system detection, sizing, & reporting capabilities. This paper focuses on the recent collaboration between ExxonMobil and PII, to investigate system capabilities with respect to “Pinholes”, to address a known threat to a specific pipeline in the United Kingdom. This paper will describe the: • Evolution of the “Pinhole” specification that captured the interest of ExxonMobil. • Use of Finite Element models to predict entitlement for characterization of “Pinhole” type defects • Detail of and results from the ExxonMobil sponsored test program that was conducted in early 2013 • The in-line inspection, analysis report, and dig verification that followed for the pipeline in question. This joint paper, prepared and presented in collaboration by ExxonMobil & PII, will reflect the perspective and synergy of the Pipeline Owner/Operator and the ILI Vendor.

Design of Pipeline Composite Repairs: From Lab Scale Tests to FEA and Full Scale Testing

Composite repair systems are used for many years to restore locally the pipe strength where it has been affected by damage such as wall thickness reduction due to corrosion, dent, lamination or cracks. Composite repair systems are commonly qualified, designed and installed according to ASME PCC2 code or ISO 24817 standard requirements. In both of these codes, the Maximum Allowable Working Pressure (MAWP) of the damaged section must be determined to design the composite repair. To do so, codes such as ASME B31G for example for corrosion, are used. The composite repair systems is designed to “bridge the gap” between the MAWP of the damaged pipe and the original design pressure. The main weakness of available approaches is their applicability to combined loading conditions and various types of defects. The objective of this work is to set-up a “universal” methodology to design the composite repair by finite element calculations with directly taking into consideration the loading conditions and the influence of the defect on pipe strength (whatever its geometry and type). First a program of mechanical tests is defined to allow determining all the composite properties necessary to run the finite elements calculations. It consists in compression and tensile tests in various directions to account for the composite anisotropy and of Arcan tests to determine steel to composite interface behaviors in tension and shear. In parallel, a full scale burst test is performed on a repaired pipe section where a local wall thinning is previously machined. For this test, the composite repair was designed according to ISO 24817. Then, a finite element model integrating damaged pipe and composite repair system is built. It allowed simulating the test, comparing the results with experiments and validating damage models implemented to capture the various possible types of failures. In addition, sensitivity analysis considering composite properties variations evidenced by experiments are run. The composite behavior considered in this study is not time dependent. No degradation of the composite material strength due to ageing is taking into account. The roadmap for the next steps of this work is to clearly identify the ageing mechanisms, to perform tests in relevant conditions and to introduce ageing effects in the design process (and in particular in the composite constitutive laws).

Systematic Approach to Measuring ILI Tool Performance

In-line inspection (ILI) tools play an important role within integrity management and substantial investment is made to continuously advance performance of the existing technologies and, where necessary, to develop new technologies. Performance measurement is typically focused for the purpose of understanding the measured performance in relation to the ILI vendor specification and for the determination of residual uncertainty regarding pipeline integrity. These performance measures may not provide the necessary insight into what type of investment into a technology is necessary to further reduce residual uncertainty regarding pipeline integrity, and beyond that, what investment, as an operator, results in an effective and efficient reduction in uncertainty. The paper proposes a reliability based approach for investigating uncertainty associated with ultrasonic crack ILI technology for the purpose of identifying efficient investment into the technology that results in an effective and measurable improvement. Typical performance measures and novel performance measurement methods are presented and reviewed with respect to what information they can provide to assist in investment decisions. Finally, general observations are made regarding Enbridge’s experience using ultrasonic crack ILI technology and areas currently being investigated.

Validation of EMAT ILI for Management of Stress Corrosion Cracking in Natural Gas Pipelines

Managing the threat of Stress Corrosion Cracking (SCC) in natural gas pipelines continues to be an area of focus for many operating companies with potentially susceptible pipelines. This paper describes the validation process of the high-resolution Electro-Magnetic Acoustical Transducer (EMAT) In-Line Inspection (ILI) technology for detection of SCC prior to scheduled pressure tests of inspected line pipe valve sections. The validation of the EMAT technology covered the application of high-resolution EMAT ILI and determining the Probability Of Detection (POD) and Identification (POI). The ILI verification process is in accordance to a API 1163 Level 3 validation. It is described in detail for 30″ and 36″ pipeline segments. Both segments are known to have an SCC history. Correlation of EMAT ILI calls to manual non-destructive measurements and destructively tested SCC samples lead to a comprehensive understanding of the capabilities of the EMAT technology and the associated process for managing the SCC threat. Based on the data gathered, the dimensional tool tolerances in terms of length and depth are derived.

Practical Applications of Bed Scour Calculations: Two Case Studies

Pipelines can be exposed at water crossings where rivers lower the channel bed. Channel bed scour may cause damage to linear infrastructure such as pipelines by exposing the pipe to the flow of water and sediment. Accurate estimation of depth of scour is therefore critical in limiting damage to infrastructure. Channel bed scour has three main components: (1) general scour, (2) bed degradation, and (3) pool depth. General scour is the temporary lowering of the channel bed during a flood event. Channel bed degradation is the systematic lowering of a channel bed over time. Pool depth is depth of pools below the general bed elevation and includes the relocation of pools that result from river dynamics. Channel degradation is assessed in the field using indicators of channel incision such as channel bed armoring and bank characteristics, through the analysis of long profiles and sediment transport modelling. Pool depth is assessed using long profiles and channel movement over time. The catastrophic nature of bed lowering due to general scour requires a different assessment. A design depth of cover is based on analysis of depth of scour for a given return period (eg. 100-years). There are three main steps to predict general scour: (1) regional flood frequency analysis, (2) estimation of hydraulic variables, and (3) scour depth modelling. Typically, four scour models are employed: Lacey (1930), Blench (1969), Neill (1973), and Zeller (1981), with the average or maximum value used for design depth. We provide herein case studies for potential scour for pipeline water crossings at the Little Smoky River and Joachim Creek, AB. Using the four models above, and an analysis of channel degradation and pool depth, the recommended minimum depth of cover of 0.75 m and 0.142 m, respectively, were prescribed. Variability between scour models is large. The general scour model results varied from 0.45 m and 0.75 m for the Little Smoky River and 0.16 m to 0.51 m for Joachim Creek. While these models are more than 30 years old and do not adequately account for factors such as sediment mobility, they nevertheless do provide usable answers and should form part of the usual toolbox in water crossing scour calculations.