In a Nutshell:
While it is the goal to obtain holistic information on pipeline material properties to reduce uncertainty and thus risk, many operators are forced to deal with various unknowns when it comes to Integrity Management (IM) decisions. Increasing expectations for improvements in addressing issues related to pipeline data and documentation that weigh on operators are resulting in the emergence of new regulations. The new regulation issued by PHMSA (Pipeline and Hazardous Materials Safety Administration) to extend IM requirements. The new regulations will result in a significant expansion of the safety requirements that apply to natural gas pipelines in the U.S.
The first set of new regulations from PHMSA regarding the safety of gas transmission pipelines will take effect on July 1, 2020. This first installment comes with a focus on Maximum Allowable Operating Pressure (MAOP) reconfirmation, verification of pipeline material properties, expansion of assessment requirements and the incorporation of API 1163 by reference. As part of MAOP reconfirmation, which aims to reconfirm a pipeline segment’s MAOP, an operator must use the pipeline’s material properties, which are Traceable, Verifiable and Complete (TVC), to represent the pipeline segment’s physical characteristics.
The Verification of Pipeline Material Properties and Attributes for onshore steel transmission pipelines is defined by Section 192.607. This new section of the regulation can be thought of as a tool for establishing physical material properties for pipe to support fulfillment of the requirements in MAOP reconfirmation; analysis of predicted failure pressure; and Integrity Management related to threat identification, data gathering and integration, Figure 1. The efforts associated with Section 192.607 Verification of Pipeline Material Properties and Attributes will be to establish a pipeline segment’s:
- Wall thickness
- Seam type
- Yield strength and ultimate tensile strength (grade)
- Toughness (where necessary)
Figure 1 - Verification of Pipeline Material Properties and Attributes is a tool to support MAOP reconfirmation, feature assessment and Integrity Management
Effectively, pipeline operators must develop and implement procedures for establishing populations based on known information, conducting destructive and non-destructive testing, examinations and assessments to verify the material properties. Secondly, an operator would then implement an excavation program for examination of the pipe and testing. This excavation program would continue until the lesser of 150 excavations or one excavation per mile of unknown required material data (i.e. wall thickness, yield strength, etc.) have been completed. The excavation program may be scheduled or leverage opportunistic pipeline exposures. If a pipe material that was not intended is discovered at an excavation site, then the program must include a plan to extend the number of excavations for that population – and the newly discovered material – until a 95 percent confidence level is achieved.
ROSEN understands the value of data-based decision-making processes and the continuous value proposition of in-line inspection (ILI). Leveraging ILI, an engineering approach to establish material properties can be implemented to deliver a programmatic approach to identifying populations based on physical pipe characteristics and targeted in situ field examinations. This approach provides an accurate picture of all populations within the section, making it possible to define an optimized and streamlined excavation program to achieve or exceed compliance. Accurate knowledge of populations also ensures that unexpected findings do not occur during the excavation program, which would require an extended sampling program.
An ILI-led approach also provides a superior mechanism for identifying outliers and understanding how to deploy resources to reduce risk. If sound joint-by-joint information is not used to establish populations, then it is possible to not know where the outliers are located and thus fail to achieve complete knowledge of existing material characteristics. Figure 2 demonstrates how deploying a program for in-field examinations without sufficient information and leveraging opportunistic exposures may miss a high-risk outlier even when complying with minimum regulatory requirements.
Figure 2 - Prescriptive compliance with 192.607 may not reduce risk optimally
As part of Integrity Management, ILI has been mostly deployed since early 2000 using conventional geometry and metal-loss-based technology in gas transmission pipelines. These datasets can be used to create the foundation for establishing populations using physical characteristics such as wall thickness (WT), joint length (JL) and, in some cases, the manufacturing process used to form the pipe (long seam welded or seamless pipe). ILI can also enable pipeline-mapping services, RoGEO XYZ, to provide the ability to execute highly accurate plausibility checks of the derived populations through a route analysis.
In many cases, ILI systems have been deployed to assess for long seam integrity threats using a combination of circumferential Magnetic Flux Leakage (CMFL) ILI and/or Electro Magnetic Acoustic Transducer (EMAT) ILI. These two technologies can often provide sufficient information on the characteristics of the seam welding process to augment populations. While these existing ILI technologies can identify differences in pipe attributes, they cannot detect differences in material properties, which are critical for a reliable population assessment. ROSEN’s RoMat PGS ILI system provides yield strength (YS) and ultimate tensile strength (UTS) for each joint of pipe, meaning the populations can be defined in more detail. Leveraging joint-by-joint data for WT, JL and YS can facilitate a sound process to deriving populations. Figure 3 shows the YS data for a number of populations with different strength values and other attributes that make up the population characteristics. These distinct populations can now be examined in the field for validation of records, and the results form Pipeline DNA, a comprehensive understanding of properties and attributes of the pipeline’s material makeup.
Figure 3 - Populations along a pipeline length identified by the pipeline DNA process and shown as a function of YS
Representing the YS data of a population as a histogram, as in Figure 4, increases confidence in assigning the grade of pipe for the population and is representative of how grade would be assigned in the pipe manufacturing process. Establishing this statistical strength distribution unlocks the next phase of the process, in which in situ examination and testing are conducted and integrated with the ILI data. The benefit of 100 percent sampling of pipes from ILI is combined with state-of-the-art in situ techniques to both fulfill API 1163 and complete the 192.607 process. Through a Bayesian statistical approach, the ILI data can be integrated with the in situ data to provide a material property assignment with only one excavation in a given population. As an alternative process to the onerous “1 per mile” requirement defined in the standard 192.607 approach, this represents a significant reduction in the number of excavations while retaining a valid and rigorous statistical approach at a defined confidence level. Further in situ data may then be opportunistically collected to reduce conservatism in the material property assignment.
While ILI and Pipeline DNA can provide high confidence in understanding the material composition of a piggable segment, excavation-based examinations in the ditch further increase the level of confidence. Leveraging detailed visual inspections, etching for steel microstructure and complementary non-destructive testing, the material assessment provides the details necessary to satisfy the demands of all regulatory requirements as described in Figure 1. We see in Figure 4 how understanding the microstructure can increase confidence in the ability of RoMat PGS to discriminate between different materials with high confidence, as the ILI system is sensitive to changes in the microstructure of steel.
Figure 4 - The primary population's microstructure is on the left, and the outlier identified by RoMAT PGS and Pipeline DNA is on the right
ROSEN has developed all these aspects into a material verification service framework centered on an engineering assessment. Named Pipeline DNA, it incorporates existing records, ILI data, in situ field examinations, material testing and industry expertise to establish populations, identify outliers and, ultimately, verify the material properties required by 192.607: wall thickness, diameter, seam type, yield and ultimate tensile strength, and toughness.
The bottom line: 192.607 Verification of Pipeline Material Properties and Attributes will be a process that can be used to establish pipe properties by defining populations and satisfying a specific number of excavations and pipe material tests. In some cases, this prescribed process will be suitable, but ROSEN’s Pipeline DNA engineering assessment can be leveraged, along with ROSEN’s RoMat PGS, to deploy an optimized excavation campaign to comply with 192.607, reduce risk by identifying outliers, improve material records and asset knowledge, and focus expenditures.