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

Abstract

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.

Output-Only Structural Health Monitoring for Deepwater Risers: Experimental Study of Wavelet Modified SOBI and Distributed Force Index Algorithm

“…Safety issues and deepwater conditions keep radiography away from deepwater risers. According to Lozev et al, 3 other new techniques like infrared thermography 6 and acoustic emission 7 technique are not applicable at deepwater scenarios.…”

“…Hence, additional remotely operated vehicle is needed. For short-range UT 4 , its applicability in deepwater risers is excluded by its requirement of clean and smooth surface of the pipe and couplant to ensure the attachment and transmissibility between sensor and pipe surface. Long-range UT 5 can only transmit around one wavelength of the guided wave into the riser, which results in neglecting the internal defects like corrosion if the wall of the riser is thicker than the wavelength.…”

“…Hence, various non-destructive evaluation (NDE) methods have been introduced to the field of riser inspection. 3 Typically, we can classify them into the following categories: Visual Inspection, Ultrasonic Technique (UT), Radiography, Electro-magnetic methods, Vibration based NDE and other techniques. The effectiveness of these NDE methods for detecting damage in deep water risers has not been evaluated or demonstrated.…”

Ultrasonic thickness structural health monitoring photoelastic visualization and measurement accuracy for internal pipe corrosion

“…In an effort to assess the state of art and identify potential improvements in measurement capability, prior reviews of inspection technology for corrosion 7 and pipe systems [8][9][10] as well as general NDE sources [11][12] are referenced.…”

Nondestructive Detection of Tilted Planar Flaws on Back Surfaces Using Ultrasonic Wave Interference

“…Inclined flaws such as stress corrosion cracks change the reflection efficiency, which is a basic parameter of the amplitude-based sizing approach, when adapting an ultrasonic pulse-echo method for nondestructive inspection (3) . The signal-to-noise ratio is the dominant factor in determining the detection limit of the ultrasonic pulse-echo method (4)(5)(6)(7)(8) . The signal available for measurement by the interference of waves attains a higher signal-to-noise ratio, because random noise does not show interference, and only the interference due to the existence of flaws is measured.…”