Thomas A. Bubenik

A Practical Approach to Pipeline System Materials Verification

The Pipeline and Hazardous Material Safety Administration (PHSMA) has increased emphasis on records that are “traceable, verifiable, and complete.” Organizing records into a document structure that is traceable, verifiable, and complete can be a daunting task.Through work with operators, Det Norske Veritas (U.S.A.) Inc. (DNV) identified a methodology to efficiently search and organize material property data and records into a structure that is fit for regulatory audit. The methodology consists of four steps:(1) Search/Organize Documentation.(2) Digitally Capture Paper Documents.(3) Determine Document Precedence.(4) Create a Reference-able Listing.The first step reviews all files and records and identifies records that are pertinent to properties verification. The search is conducted at an operator’s office(s) by a team of personnel familiar with pipeline construction and maintenance documentation.Once records have been identified, they are digitally captured (scanned) making them easy to reference. This requires a set of metadata and unique name for each document. The metadata consists of project number, document type (maintenance form, drawing, etc…), pipeline name, and information location.Document precedence is used to identify documents most likely to contain correct material information. Document precedence is determined with operator employees that can identify document(s) that have been historically given high reliability.Finally, a listing tabulates material properties along with the unique document name(s) for the specific records. The listing contains pipe (by segment or joint), fittings (valves, prefabricated elbows, etc…), and other components that may affect Maximum (Allowable) Operating Pressures. Typically the listing uses linear pipeline stationing as the main reference.Implementation of the methodology yields a listing of material properties specifically linked to a digital document database — i.e., a records system that is “traceable, verifiable, and complete.” In addition to material properties, this methodology has also been applied to risk-related information (e.g. cathodic protection, crossings, coating information, etc…). The listing can then be used to identify any information gaps and potentially prioritize them based on reliability.Copyright

Application and Validation of Statistically Based Corrosion Growth Rates

When it comes to managing the integrity of corroded pipelines, operators are confronted with many difficult decisions — one of which is the level of conservatism that is used in pipeline integrity assessments. The financial implications associated with excavation, repair, rehabilitation, and inspection programs typically balance the level of conservatism that is adopted. More conservative approaches translate into more spending, so it is important that repair strategies developed based on the integrity assessment results are effective.As integrity assessment methodologies continue to evolve, so does the ability to account for local conditions. One development in recent years has been the ability to evaluate multiple MFL in-line inspections to determine areas of active corrosion growth, through the combined use of statistics, inspection signal comparisons, and engineering analysis. The authors have previously outlined one approach (commonly known as Statistically Active Corrosion (SAC)) that has been successfully used to identify areas of probable corrosion growth, predict local corrosion growth rates, and maximize the effectiveness of integrity assessments.[1]Validation of the SAC-predicted corrosion growth rates is important for establishing confidence in the process. This is achieved through inspection signal comparisons, integrating close interval survey (CIS) results, and (when possible) field verification. The means by which these methods are used for validating the SAC method are described in this paper.Copyright

IMPROVED COMPARISON OF ILI DATA AND FIELD EXCAVATIONS

The importance of comparing in-line inspectio n (ILI) calls to excavation data should not be underestimated. Ne ither should it be undertaken without a solid understanding of t he methodologies being employed. Such a comparison is not only a key part of assessing how well the tool performed , but also for an API 1163 evaluation and any subsequent use of the ILI data. The development of unity (1-1) plots and the associ ated regression analysis are commonly used to provide th e basis for predicting the likelihood of leaks or failures from unexcavated ILI calls. Combining such analysis with statistica lly active corrosion methods into perhaps a probability of exc eedance (POE) study helps develop an integrity maintenance plan for the years ahead. The theoretical underpinnings of standard reg ression analysis are based on the assumption that the indep endent variable (often thought of as x) is measured without error as a design variable. The dependent variable (often lab eled y) is modeled as having uncertainty or error. Pipeline c ompanies may run their regressions differently, but ILI to f ield excavation regressions often use the ILI depth as the x variable and field depth as the y variable. This is especially the case in which a probability of exceedance analysis is desired invol ving transforming ILI calls to predicted depths for a co mparison to a threshold of interest such as 80% wall thickness. However, in ILI to field depth regressions, both the measured d epths can have error. Thus, the underlying least squares reg ression assumptions are violated. Often one common result is a regression line that has a slope much less than the ideal 1-1 relationship.

AN APPROACH FOR EVALUATING THE INTEGRITY OF PLAIN DENTS REPORTED BY IN-LINE INSPECTION TOOLS

Current federal regulations in the U.S. require excavation of plain dents identified through in-line inspection surveys based primarily on depth. Industry experience, and previous research, has shown that the depth of the dent, alone, is not sufficient to assess dent severity and that releases could occur at dents below the excavation threshold (Dawson, 2006). Canada’s National Energy Board released a safety advisory on June 18, 2010, to all companies under their jurisdiction regarding two incidents involving shallow dents. The safety advisory stated that all integrity management programs should be reviewed and updated where appropriate to address the threat posed by shallow dents. Similar incidents have raised awareness in the United States and elsewhere around the world. This paper focuses on the fitness for service of dents identified by in-line inspection surveys. The fitness for service assessment provides an estimated remaining life of a dent based on the geometry of the dent and current pressure cycling of the pipeline. Dynamic pressure cycling at each dent location is estimated using the upstream and downstream pressure cycle data, elevation, and distance along the pipe. The dynamic pressure cycle data at each dent is then converted into equivalent stress cycles based on the results of rainflow cycle counting. Maximum strain levels of the dents are calculated based on the geometry of the dent as determined by radial sensor measurements from the in-line inspection survey. The combination of assessment methods provides estimates of remaining fatigue life and peak strain which can be used for prioritizing the investigation and remediation of plain dents in pipelines. Finite element analysis (FEA) is performed for one dent to calculate the maximum strain levels and identify stress concentration areas. These results are compared with the values applied during the fitness for service assessment to validate the accuracy and conservatism of the calculation methods used. An idealized dent will be analyzed to investigate the strain calculations in ASME B31.8 and localize maximum strain values.

Stress corrosion cracking

Abstract Stress corrosion cracking (SCC) of buried pipelines has been a recognized threat since 1965. Two forms of SCC exist: high pH SCC and near-neutral pH SCC. Coating type and condition have the strongest effect on SCC initiation and growth. High pH SCC occurs more frequently on coal tar coated pipelines, whereas near-neutral pH SCC is more likely on tape coated lines. The local environment and operating stress characteristics are also important factors. Industry guidelines have been proposed elsewhere to identify where high pH SCC and near-neutral pH SCC are most likely. There have been instances of SCC when these guidelines are not met, most notably at stress levels below 60% of the specified minimum yield stress.

A Practical Approach to Continuous Quality Control of Pipeline System Records

In recent years there has been an industry wide initiative to verify operating pressures by reviewing source records and ensuring they are traceable, verifiable, and complete. A methodology was presented in a recent paper (A Practical Approach to Pipeline System Materials Verification by Lutz and Bubenik) to systematically review and organize records into an auditable framework (i.e. a GIS compatible listing or database). Once operators have completed their systematic records review, they are advised to maximize their investment by performing appropriate on-going records maintenance.An effective records maintenance program will include the following elements to ensure effective management-of-change and continuous quality assurance and quality control. 1. Source documents will be made available to the company engineers and technicians that use the verified information to make everyday integrity and operational decisions (i.e. use a GIS interface to link verified information to the source documents). 2. A controlled process for management-of-change that effectively integrates new construction and replacement records into the existing database. 3. Continuously verify and cross-check pipeline system material properties with… a. …destructive material testing of any pipe that is removed or replaced. b. …in-the-ditch NDE methodologies, such as UT wall-thickness measurements and hardness to yield strength testing. c. …global survey data such as GIS and in-line inspection. 4. A controlled process to resolve records failures that includes the following steps: a. Identify and isolate the data point(s) that are the cause of the records failure. b. Establish a boundary around the potential extents of the records failure. c. Systematically investigate within the established boundary and verify the data discrepancies until the records failure is resolved to a reasonable certainty.By implementing a records maintenance program with these elements, operators will ensure that their records database will be maintained and that the information being relied upon for daily integrity and operational decisions is reliable. Operators will decrease the likelihood of issues resulting from records failures and will ensure their records organization will with stand the scrutiny of future audits and records investigations.Copyright

POTENTIAL COMPONENTS OF AN EFFECTIVE LSW INTEGRITY MANAGEMENT PROGRAM

Det Norske Veritas (U.S.A.), Inc. (DNV) has had the opportunity to observe and contribute to a significant number of longitudinal seam weld integrity management programs. DNV has used these opportunities to identify activities with a positive impact on the integrity management of the longitudinal seam welds for which they are implemented. The Integrity Assessment activities identified by DNV include those pertaining to hydrostatic pressure testing, in-line inspection data, and in-line inspection technology. The Anomaly Review and Prioritization activities include excavation prioritization, control excavations, and investigative excavations. The Excavation and Repair Program activities include non-destructive examination techniques, technologies and validation, repair methods, and safety measures. The Tool Validation activities include in-line inspection specification and vendor feedback. The Reassessment activities include those pertaining to in-line inspection validation, operations, and reassessment interval calculation methodologies. Not all longitudinal seam weld integrity management activities are appropriate for all pipelines. In these cases, the correct combination of integrity management activities will result in an effective longitudinal seam weld integrity management program.

Data Analysis in Parallel With GIS Systems

The processing and integration of data for direct assessment (DA) and in-line inspection (ILI) comparisons is critical to making sound integrity-based decisions. While geographic information systems (GIS) are now commonly used to model pipeline systems, most day-to-day data processing and integration occurs outside of the GIS, for example in Microsoft Excel™. As such, Det Norske Veritas (DNV) developed a data integration tool within Excel™ as part of a large scale stress corrosion cracking direct assessment (SCCDA) program for a major pipeline operator. Linear based data provided by the client (e.g., in-line inspections, girth welds, previous excavations, close interval survey, coating, grade and wall thickness, pressure history, road and water crossings, risk assessments, landowner information, etc.) is processed, analyzed and incorporated into the overlay. This tool provides the ability to integrate any linear based data in a graphical representation of the pipeline along continuous and parallel chainage. The overlay allows for identifying similar locations using criteria that are difficult to program into an algorithm and helps engineers to relate complex factors during the decision making process. The overlay also provides the ability to easily extract data relevant to sites selected for assessment along the pipeline. The data integration tool has already found many applications beyond SCCDA since it provides a robust process to integrate and analyze data in parallel with GIS systems. The overlay provides engineers with a method to make decisions without learning complex GIS programs and has the added ability to feed the results back into GIS systems. Such decision making processes and applications include direct assessment programs, cathodic protection enhancements, risk reduction programs, in-line inspection comparisons, and maintenance activities.Copyright