Re-thinking the Possible in In-Line Inspection
By: Michael McGee, Quest Integrity Group
As seen in the May 2012 edition of Offshore Magazine
Pipeline failures in the oil and gas industry continue to draw attention to the effectiveness of corrosion damage assessment methods, connected regulations, and the prerequisite for accurate understanding of the physical condition of pipelines during sustained activity. Historically, pipeline assessment methods have been treated with equal prescriptive weighting. However, coupled with an aging infrastructure and increasing demands, operators are accepting that some previous systems of measurement and evaluation may no longer be sufficient for continued safe, reliable and efficient operations.
Determining and prioritizing risk for offshore assets is generally no different than onshore assets, although the consequences of failure are often elevated. ILI remains the preferred subsea inspection method because it delivers the most effective, best potential for extensive data evaluation and comprehensive analysis fundamental to sound engineering principles. Obtaining such comprehensive pipeline data is typically more difficult due to remote locations, limited access, challenging designs, and extreme operational parameters. Inspection options become reduced whereas expenses and timelines greatly increase.
Modern inspection approach
To address the opportunity in the subsea environment, ILI tools have advanced via evolution and foresight. For instance, no longer is a constant bore or 3D minimum bend radius a precondition. Presently, there are cost-effective technologies providing modern in-line inspection solutions for challenging subsea pipelines. Quest Integrity Group’s InVista platform offers one such solution.
The proprietary technology includes is an intelligent tool capable of rapid, automated, ultrasonic (UT) inspection of unpiggable pipelines over 100 miles in length. The tool platform derives from furnace tube inspection technology and has been used to inspect refinery heater coils during short notice emergencies and plant turnarounds since the 1990s.
As a leader in taking on challenging inspections, Quest Integrity is not a conventional provider in the normal sense. By focusing only on difficult and challenging environments, the company specializes, leaving ordinary surveys for commodity vendors.
The unique navigational abilities of the InVista platform are reclassifying piggability. The tool was designed from the outset to successfully inspect and perform in challenging pipe systems. The design foregoes the risk associated with modifying conventional ILI tool configurations or attempting unproven design(s).
This advancede new technology overcomes many operational challenges in a single package:
* All tools are bi-directional (BIDI), dual-diameter capable, and navigate multi-diameter pipelines
* All tools negotiate 1.0D bends, including back-to-back and miter bends
* All tools perform in low flow / low pressure (LF/LP) environments
* All tools can be hand-carried, lifted, loaded, and transported
* Standard passage values of 25-35% standard, using dual-diameter â‰¥ 40%.
Moreover, modern data acquisition and integrity assessment methods allow the best possible understanding of actual current pipeline conditions. The new platform makes use of direct measurement ultrasonics, producing higher resolution data sets with tighter tolerance and more accurate flaw sizing. Providing this data allows precise wall thickness values and deformation data in objective, absolute figures.
Because of the unique sensor configuration, the tool remains unaffected by additional signal degradation (“noise”) that can diminish resolution and adversely affect defect characterization for tools that have sensors riding directly on the pipe surface. Confidence levels are inherently higher because the raw data is better.
Improved pipeline assessment
The magnitude of pipeline rehabilitation and repair work is greatly affected by tool tolerances. “The best tolerances result in the fewest repairs” ”" an old saying which can mean that an operator’s time and money is saved.
Accordingly, choosing to run tools with tighter tolerances increases operator efficiencies and decreases waste allowing more effective decision-making. It is especially important in offshore pipelines to determine whether a particular flaw exceeds established criteria for safe and reliable operation or if it will exceed criteria before the next inspection interval.
Presently, most ILI inspections in offshore pipeline systems employ tools based on magnetic flux leakage (MFL) technologies. Simply put, the MFL data sets record influences to a calibrated magnet circuit based on nominal wall-thickness throughout a pipeline. Defects are identified, subjectively interpreted, and then depicted or “boxed,” using length and width with a rectangle containing the corresponding wall loss data dimensions of flaws. Modern software enables analysts to estimate the geometry of the flaws (e.g., parabolic or river bottom shape) to create a richer qualitative characterization.
While software manipulation of MFL data to characterize the shape of individual flaws makes sense conceptually, it does not reduce the inherently broad tolerances in the data or increase an operator’s confidence that an indicated flaw merits excavation or further study. Such flaw-by-flaw basing in conjunction with verification is known to be resource intensive.
Compared with MFL tools, direct measurement UT inspection offers a higher return in investment due to accuracy driven efficiencies and providing superior results. UT inspection outputs a digital map of individual wall-thickness readings, ideally suited to effective area assessment methods such as RSTRENG and API 579 Level 2 Remaining Strength Factor (RSF) calculations.
By rapidly processing large quantities of ILI wall loss data and evaluating the MAOP at distinct locations, ranking of these MAOP values serves as a rational and rapid means for prioritizing the severity of corrosion throughout a pipeline. With UT’s improved confidence and precision, operators are able to increase profitability, maximize resources and prepare more effective risk mitigation.
Value in understanding
Offshore operators of all sizes seek ways to minimize expenditures relating to operations while at the same time maintaining safe, profitable, and compliant inspection programs. Since inspections and repairs are usually budgeted years in advance, it makes sense to plan as well as possible.
The FFS Level 2 assessment of metal loss determines an effective-area method where a “river bottom” profile is constructed from the wall thickness measurements, and these are used to compute revised MAOP ratings (API 579-1/ASME FFS-1 2007). These calculations are typically performed over joint sections between girth welds of pipe, although a single rating may be assigned for an entire pipe section.
Using this method results in a more technically sound MAOP and is less intensive and less subjective than flaw boxing. These advanced assessments provide the operator with greater value from each individual inspection, and now the operator can be proactive instead of reactive, addressing issues with the pipeline before problems arise.
Case study 1
Quest Integrity was approached to inspect three South American subsea pipelines. Line 1 was an 8-in. crude line running from a platform to shore. A geometry survey determined the scheduled MFL inspection would be blocked due to restrictions. InVista measured the minimum internal diameter (ID) at 6.77-in . (172 mm ). More surprising was the identification of a 5-ft (1.5-m) section where a sleeve had been used for repair. The ID in this section expanded from 8.03-in. (204-mm) to 9.25-in. (235-mm ) which would have stalled out most ILI tools.
Case study 2
In the Persian Gulf, Quest Integrity was asked to inspect a subsea pipeline that had been dormant for 2.5 years. The 6-in. multi-phase infield wellhead-to-production platform pipeline had been mothballed and no traps installed. Turnkey scope included supply of traps, connection hoses, cleaning, inspection, analysis, and providing a full FFS pipeline assessment report (API Level II). The engineering deliverable was valuable information for the client because they planned to reinstate the line for use following a $5 MM drilling investment.
InVista identified wall thickness changes that were not in the as-built drawings and defects in that thinner section. Only minimal cleaning was required due to tolerance of the inspection tool; and so only two foam pigs runs were required. Good data was gathered, and the entire survey was completed in < 1.5 hr.
As-built drawings stated 0.562-in. wall (14.3-mm) for some pipe sections. However, InVista provided actual wall thickness data at 0.405-in. (10.3-mm) and identified an area of external corrosion in this thinner wall with 41% metal loss.
The client was pleased with the complete inspection of its pipelines. Some of the noted advantages associated with new the technology were:
* No infrastructure modifications were required; geometry and wall thickness data provided in a single run, resulting in a cost savings for the operator
* The lightweight handheld tool was loaded into and unloaded from a single launch point, resulting in reduced safety concerns and increased operational capabilities
* Superior navigational capabilities including short radius back-to-back, unbarred off-takes, and pipe schedule changes including heavy wall
* Bi-directional, low flow/low pressure and industry leading minimized tool passage requirements
* Fully integrated, API 579 Compliant Level 2 FFS assessment included as standard deliverable.
Advances in modern approaches and comprehensive data assessment for in-line inspection of challenging subsea pipelines offer material improvements over past methods. Historically, the sequence of gathering overly conservative ILI data or reduced quality created a great deal of extra work, frittered away time, depleted scarce budgets, and inhibited proper prioritization.
Considering the corrosion causes and flaw calculations is critical in determining the remaining working life of the pipeline asset, its inspection interval, future repairs, and operational efficiencies. Using modern approaches, offshore operators have a better understanding of the physical condition of the pipe and the unique degradation mechanisms affecting it.
The author would like to recognize and thank the Quest Integrity Group contributors who supported this paper–Nigel Baxter, Geert Bontekoe, Dan Revelle, Margo Reyna, George Simmonds and Ray Whaley. Based on a paper presented at the Pipeline Pigging and Integrity Management Conference, February 6-9, 2012, in Houston, Texas.
About the Author
Michael McGee is a technical advisor for Quest Integrity Group’s Pipeline Division, a position he has held since 2009. Before joining Quest Integrity, McGee spent six years with Rosen Inspection Technologies working his way up from field technician to lead area manager–technical services for North America. He has more than 10 years of oil and gas industry experience, along with more than 20 years of experience in project execution and key account management. In addition to providing client-centered pipeline integrity solutions since 2003, Michael lectures for the Petroleum Extension Service (PETEX) of The University of Texas at Austin.