SEPTEMBER 2014 VOLUME 11, NUMBER 1
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New proposed additions to the Pipeline and Hazardous Materials Safety Administration (PHMSA) integrity management program may require operators to test pipe segments located in high-consequence areas (HCAs) and to "devote additional focus, efforts, and analysis…to ensure the integrity of [those] pipelines."1 With these additions come Integrity Verification Process (IVP) regulations.
As it stands now, these requirements would mandate pipeline operators to verify maximum allowable operating pressure (MAOP) and material properties of gas transmission lines, including pipelines constructed before 1970 that had previously been grandfathered from testing protocols.
Recognizing that new methodologies and technologies are needed to improve the accuracy and reduce the costs associated with these new integrity inspections, GTI is working with industry partners, with funding from OTD, to fill technology gaps.
Until recently, any pipeline with an unknown yield strength was assigned a conservative value of 24,000 psi. As a result, many pipelines were calculated to be operating at more than 20% specified minimum yield strength (SMYS), even though they were likely operating below 20% SMYS. Destructive testing was the only alternative operators had to accepting that inaccurate assumption, which is a cumbersome process. The large sample sizes required by the API 5L specification often necessitate a line shutdown or a bypass system.
In a project designed to provide a better option, the GTI team is investigating methods for nondestructive material property testing, including surface indentation and other surface measurement techniques. GTI has launched a new research program whose goal is to quantify the potential variability of material properties, so that surface measurements can be used with the appropriate safety factors, based on vintage and other relevant characteristics.
The scope of this project includes the development of factors that will correlate surface properties with through-wall material properties based on vintage. GTI will identify the manufacturing processes and related pipe vintages that resulted in non-homogenous pipe and will develop correlation factors that account for the potential through-wall variations. These factors will be in the form of probabilistic confidence intervals based on vintage by decade and manufacturing process.
"The ability to characterize material properties, particularly yield strength, of in-service pipelines without taking the line out of service or removing samples will significantly reduce the cost of complying with existing and pending federal regulations," says Daniel Ersoy, GTI R&D Executive Director. "Backfilling records with material property information such as yield strength and toughness also improves integrity management through system knowledge that allows enhanced modeling and analysis."
GTI researchers have also validated a methodology with the potential to provide superior confidence compared with the prescriptive sampling interval currently required by integrity management regulations (49 CFR Part 192). The new technique uses adaptive sampling that updates the required number of samples based on results achieved to date.
"Using this method, operators will be able to classify pipeline segment properties with a known confidence level and to determine the likelihood of a 'weakest link' section," says Ersoy. "If the data and code allow, operators may be able to reduce the overall number of samples required to verify the material properties of a line segment, while simultaneously providing confidence levels on material property measurements."
One of the implications of pending IVP regulations is that operators may be required to hydrotest pipelines operating above 20% SMYS in an HCA that did not have a post-construction hydrotest. Yet, the hydrotesting process can create operational and engineering concerns such as residual water and potential sub-critical crack growth.
Photo provided courtesy of Quest Integrated (Qi2)
This situation creates a need for options to hydrotesting that would provide equivalent assessments. GTI researchers are attempting to validate that in-line inspection (ILI) tools can provide an assessment that would find any defect that would fail a hydrotest. Partnering with Quest Integrity, a recognized leader in the development and delivery of asset integrity management and asset reliability solutions, they are creating critical flaw curves for various pipe configurations (yield strength, diameter, wall thickness and % SMYS)— ranging from smooth metal loss flaws to sharp planar cracks—in order to develop a calculator that will enable operators to use ILI tools on a specific line segment to provide a hydrotest equivalency.
"Technologies like electromagnetic acoustic transducer (EMAT) are particularly promising for their ability to detect the critical flaws that would fail a hydrotest," says Ersoy. "We're working with the appropriate stakeholders to generate a technically sound basis for regulatory acceptance of these assessment techniques to provide operators with an alternative to hydrotesting."
Proposed IVP regulations may present yet another challenge for operators: They may need to provide "validated traceable materials documentation" for the thousands of fittings in their system. Where they do not have "mill-equivalent" or design and material documentation for their fittings and components, they may need to cut them out or de-rate their pipelines.
GTI researchers are working on tools that will help operators identify the material properties of their fittings and reduce the cost of gathering and compiling information. The first step will be a catalog of legacy fittings and components designed to help operators identify and characterize the material and mechanical properties of their assets. It will include images, descriptions, strength class ratings, and material and mechanical properties for vintage and legacy fittings, appurtenances, ells, tees, valves, and more—as well as the material design and strength classes they were manufactured to—so that operators can, at a minimum, assign conservative assumptions about the fittings’ properties.
The catalog will also include information about the location of component markings and/or distinguishing features such as flange thickness and bolting patterns. The GTI team is also working with manufacturers and operators to collect supplemental information, including a breakout by manufacturer year and/or vintage, where possible.
Some pipe segments classified as transmission may be subject to IVP regulations, yet they include significant portions that are unpiggable, or difficult to inspect with conventional ILI tools.
GTI researchers are working with industry-leading inspection technology providers to develop technologies that operators can use to reduce their exposure to integrity threats and unknown pipe defects when inspecting segments of unpiggable pipe. For one potential solution, GTI researchers are working with industry partners to enable the application of magnetic flux leakage (MFL) technology for live inspection of short unpiggable pipeline segments using a modified and patented MFL technology. "The need is particularly urgent for cased and uncased pipelines under railroads, highways, and smaller river crossings," says Dr. Kiran Kothari, Institute Engineer at GTI. "Until now, it’s been very expensive and challenging to inspect these lines."
Another technology, Pipecrawler, an inspection platform for unpiggable pipe supported by GTI and OTD, comprises a tethered inspection platform that uses brush-drive units powered by electric linear-drive motors for propulsion. The current version, which features MFL sensors, has the ability to inspect up to 3,000 feet of pipe in pressures up to 700 psi and to access a pipeline from a single location. Pipecrawler also has EMAT sensors and they are working on an internal guided wave sensor.
EMAT is another promising technology that offers the ability to detect and characterize corrosion, stress corrosion cracking (SCC), cracks, mechanical damage, laminations, coating disbondment, and lack-of-fusion that can be used in live natural gas pipelines without a liquid couplant. The technology comprises an ultrasonic transducer (UT) sensor that uses alternating current in a wire to induce an eddy current that can identify and characterize many defects—planar or tight-fitting cracks, in particular—that traditional MFL cannot. Recent advances in the technology have enhanced performance, including improved probability of detection (POD) and probability of identification (POI) for anomalies.
While there are EMAT tools available from several vendors designed for conventional in-line inspections, GTI is working to transfer third-generation EMAT tools that offer additional applicability for smaller-diameter, lower-pressure lines. GTI has partnered with Quest Integrated (Qi2) to bring the capabilities of its existing technology to the natural gas industry. Currently, a prototype EMAT sensor that is bidirectional and collapsible is being developed, which will be tested for sensitivity and wear resistance.
For more information contact Paul Armstrong.