Evaluation of Methods for Detecting and Monitoring of Corrosion Damage in Risers

[+] Author and Article Information
M. G. Lozev

 Edison Welding Institute, 1250 Arthur E. Adams Drive, Columbus, OH 43221-3585Mark_Lozev@ewi.org

R. W. Smith

 U.S. DOT, Washington, D.C.Robert.W.Smith@dot.gov

B. B. Grimmett

 BWXT, Lynchburg, VAbbgrimmett@yahoo.com

J. Pressure Vessel Technol 127(3), 244-254 (Apr 15, 2005) (11 pages) doi:10.1115/1.1991877 History: Received March 03, 2005; Revised April 15, 2005

Offshore pipeline failure statistics have been collected for more than 30 years now and illustrate that the riser predominantly fails as a result of corrosion. The consistent wetting and drying in the splash zone combined with defects in the coatings are the usual contributors to the problem. Risers are inspected at some determined frequency and can be done by internal and external methods. Inspecting by either means brings into account caveats and limitations from the technology used as well as human factors. For example, external inspections can be inefficient and inaccurate with some tools missing defects in areas of coating disbondment. In addition, internal inspections sometimes create false positives and can miss defects. These inaccuracies in the technologies or the techniques used may miss defects that eventually lead to failure. On the other hand, using corrosion mapping and fitness-for-service (FFS) assessment from the data collected, along with the inherent conservatism of this data from limited measurement accuracy, may result in the premature replacement of risers. A literature search is being conducted to review existing riser inspection methods and identify candidate nondestructive methods for riser inspection. These methods should be capable of detecting and monitoring general corrosion, localized corrosion pitting, and stress-corrosion cracking (sulfide or hydrogen induced) as external or internal corrosion damage. Thus far, this search has found that assessing the remaining service life of aging risers is largely dependent on the accuracy of analyzing corrosion damage to the riser surface in the atmospheric, splash (tidal), submerged, and buried environmental zones. The accuracy of each technology was analyzed. The capabilities and limitations of each method/technique used for riser inspection are summarized. The investigation is focused on long- and short-range ultrasonic techniques used for initial screening and corrosion mapping. These techniques can be deployed to detect a significant reduction in wall thickness using guided and torsional waves or to map accurately a corrosion damage using single/multiple transducers and phased-array probes in manual or automated mode. A pulsed eddy-current technique that uses a stepped or pulsed input signal for the detection of corrosion areas under insulation (CUI) is also being evaluated. This allows the detection of wall-thinning areas in the riser without removing the outside coatings. In addition, it is found that filmless, real-time, and digital radiography can be used to find internal and external corrosion defects in an insulated splash zone while the riser remains in service. A survey of nondestructive evaluation (NDE) manufacturing companies, NDE inspection companies, and operating companies was completed to collect information about current instrumentation and inspection/operators’ experience for riser inspection. Examples of advanced riser inspection instrumentation and field results are included. The ability of the candidate technologies to be adapted to riser variations, the stage of standardization, and costs are also discussed.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Anticipated riser corrosion phenomena

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Figure 2

General pipeline failure statistics for Gulf of Mexico (Source: DOI/MMS)

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Figure 3

Location of the damage (Source: DOI/MMS)

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Figure 4

Location of damage due to external corrosion (Source: DOI/MMS)

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Figure 5

Location of damage due to internal corrosion (Source: DOI/MMS)

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Figure 6

Automated ultrasonic corrosion mapping and imaging using phased-array transducers

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Figure 7

Guided wave responses–RF signal (left) and processed signal (right) (courtesy SwRI, U.S.)

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Figure 8

Pulsed eddy current thickness measurements (courtesy RTD, The Netherlands)

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Figure 9

Digital radiography results (courtesy SwRI, U.S.)

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Figure 10

Short-range UT instrumentation–riser inspection tool and automated ultrasonic corrosion mapping using riser inspection tool non-damaged area (top C- and B-Scans) and external corrosion (bottom C- and B-Scans) (courtesy RTD, The Netherlands)

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Figure 11

Riser inspection using long-range guided ultrasonics equipment (top pictures courtesy Guided Ultrasonics Ltd., U.K.; bottom picture courtesy PI Ltd., U.K.)

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Figure 12

Riser inspection using pulsed eddy-current equipment (courtesy RTD, The Netherlands)




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