Robotic Magnetic Flux Leakage (MFL) Sensor for Monitoring and Inspection of Deepwater Risers Graduate Student Design Project

07121-DW1603D

Goal
This project seeks to advance the development of inspection robots and nondestructive evaluation sensors for the on-site inspection of risers used in deepwater offshore platforms. The new idea in this study is to model, develop and test promising nondestructive testing (NDT) technologies such as magnetic flux leakage (MFL), that can be incorporated into tether-less, mobile, remotely operated robots to detect defects and fatigue cracks inside installed risers, in real time. The project will also develop new damage detection algorithms and correlate the results of the MFL technique with the results of existing techniques.

Performers
Rice University, Houston, TX 77251
iTRobotics, Houston, TX 77251

Background
As water depths in excess of 3000 meters are reached, the task of designing deepwater riser systems faces unique challenges. Serving as the conduit between the subsea wellhead and the production topside platform, for production, gas lift or water injection purpose, riser systems can be either rigid or flexible. Riser types include vertical top tensioned risers, steel catenary risers, and flexible pipe risers, each with their own potential failure modes. Calculating fatigue life is a very complex problem, especially when considering factors such as corrosion. The analysis and measurement of deepwater riser response is complex due to vessel motions, vortex induced vibrations, and soil-structure interaction.

Risers have to be designed for high pressure loads and dynamic loading due to current, waves, vessel motion. In addition, risers in the Gulf of Mexico are subjected to extreme storms which produce large vessel offset, tilt and heave. They are also subjected to fatigue loading due to loop and eddy currents that produce vortex induced vibrations. The overall limited number of deepwater riser developments have necessitated the evaluation of component failure risks using real-time monitoring and instrumentation systems that are designed to provide feedback on performance, alert operators of adverse conditions for appropriate corrective action, and ensure that the risers operate without failure.

The traditional approach to offshore riser monitoring is through measurement of vessel motions and the application of complex theoretical models to estimate the riser shape and response. However, for ultra-deepwater risers, new techniques of monitoring, inspection and repair are needed. Steel catenary risers and flexible risers are difficult to inspect and repair on-site, but the consequences of failure in ultra-deepwater fields will worsen.

Deliverables for this project will include a series of reports on the tasks as they are completed and a final report integrating the results of the project.

Potential Impacts
Development of the on-site inspection robots and nondestructive techniques for riser inspection will serve as a preventative maintenance measure for ensuring the stability and extending the life of deepwater riser systems. This will serve to help prevent costly downtime or accidents from occurring, leading to the avoidance of lost production and a reduction in the risks of environmental damage.

Accomplishments
Work on this project began on October 16, 2008 and as of yet there have not been any major accomplishments to report with this initial summary.

Current Status
This project includes two major elements: (1) development of a detailed analytical model of a deepwater semi-submersible platform and risers, with coupled analysis floating platform/mooring/risers, and the establishment of the dynamic response of riser for fatigue crack evaluations, and (2) experimental evaluation of a remotely operated nondestructive evaluation sensor on a small scale finite section of the riser, under the dynamic response to which the riser is subjected under normal and adverse operating conditions.

Work has begun on two initial tasks: the development of the Project Management Plan with work breakdown structure that concisely addresses the objectives and approach for each task with all major milestones and decision points, and the development of a Technology Status Assessment describing the state-of-the-art of the proposed technology. The key tasks to be undertaken following the submission of the Project Management Plan and Technology Status Assessment are outlined below.

1. Analyze an ultra-deepwater semi-submersible platform and risers, with coupled analysis floating platform/mooring/risers and evaluate the riser response.

2. Experimentally evaluate a remotely operated nondestructive evaluation sensor on a small scale riser (to be done at Rice University in collaboration with itRobotics).

3. Subject the riser pipe scale model with the robotic crawler and MFL sensor to dynamic loads . New real time damage detection algorithms based on system identification and control theory will be developed to detect damage. The ability of the sensor to detect wall thickness changes due to cracks will be evaluated.

4. Evaluate the concept of using magnetic permeability sensors (based on a correlation between the changes in the magnetic permeability of magnetic materials, such as ferritic steels and the applied stresses), using a probe to measure the electromagnetic field close to the surface of the steel pipe.

5. Perform a detailed comparison of the analytical and experimental results to establish reliable techniques to estimate fatigue response and failure. Evaluate the effectiveness of the developed damage detection algorithms and correlate the results of the MFL technique with the results of existing real time monitoring carried out with fixed sensors on deepwater risers.

Project Start: October 14, 2008
Project End: October 13, 2010

DOE Contribution: $ 120,000.00
Performer Contribution: $ 30,000.00

Contact Information:
RPSEA – Jim Chitwood (jchitwood@rpsea.org or 713-372-2820)
NETL - Jay Jikich (Sinisha.Jikich@netl.doe.gov or 304-285-4320)
Rice University – Satish Nagarajaiah (nagaraja@rice.edu or 713-348-6207)

Thesis - Structural Health Monitoring System for Deepwater Risers with Vortex-induced Vibration [PDF-6.8MB] - Chaojun Huang, Rice University - June, 2012

Thesis - Magnetic Flux Leakage Robotic Pipe Inspection: Internal and External Methods [PDF-13MB] - Andrew J. Lynch, Rice University - December, 2009