Proceedings of OMAE ‘03 22nd International Conference on Offshore Mechanics

and Arctic Engineering June 8-13, 2003, Cancun Mexico

OMAE2003-37134

MOBILE MARINE RISER INSPECTION AND MANAGEMENT PROGRAM

Keywords: Riser Inspection, Riser Management

Chris Disher* ABB Vetco Gray Inc.

1249 Evangeline Thruway Broussard, Louisiana USA

Email: chris.disher@us.abb.com

Larry Harthorn ABB Vetco Gray Inc.

1249 Evangeline Thruway Broussard, Louisiana USA

Email: larry.k.harthorn@us.abb.com

ABSTRACT The new R.A.D.A.R. (Riser Active Data Acquisition Recorder) program allows for full marine drilling riser inspection while the joints are stacked on the deck of the rig with no disassembly. With the utilization of ultrasonics, robotic tools have been developed to pass through the inside diameter of the main tube and auxiliary lines to obtain potentially thousands of pipe wall readings and to record the weld integrity of each weld. The tools are also capable of video recording the pipe interior. Trained inspectors complete the riser survey with dimensional, visual, and magnetic particle inspections on the end connections of the main tube and auxiliary lines. Inspection data is compiled and stored in a database and is added to previous inspections and will be utilized for trend analysis. Using statistical methods the inspection history can predict trends of riser life and the potential for future repairs. This will assist operators to predict riser repairs, out of service time, cost of repairs, and most importantly eliminate extremely costly rig down time. The RADAR program has successfully inspected over 110,00 feet of pipe since its inception in September 2001. BACKGROUND A marine drilling riser is an integral part of the floating rig drilling operation, connecting the rig to the blowout preventer at the sea floor to drill through and return expensive drilling mud to the surface. Marine drilling riser generally includes a 50’ to 90’ long main tube, 16” to 21” inches x 5/8” to 1” wall and three to five smaller auxiliary

*Address all correspondence to this author

lines 3” to 6” in outside diameter x ½” to 1” wall. The assembly is incased in a set of large buoyancy floatation modules. According to the particular rig there can be up to 150 riser joints on-board reaching almost two miles in length. Along with frequent visual inspection and maintenance, a full inspection should be completed to check for fatigue flaws in welds, pipe wall thickness wear, and excessive corrosion/wear in connectors. The riser is subject to continuous tension, bending and temperature variations as well as internal and external pressures. Like other rig equipment riser requires periodic maintenance and inspection. Without proper maintenance the cost of failure can be extremely high. Failures may occur in many forms; leaking seals, malfunctioning connectors, fatigue cracking and ultimately parting of the welds resulting in dropping the riser and BOP. With proper up-keep a marine riser system can easily have a trouble free life of 25 or more years. TRADITIONAL INSPECTION Routinely contractors cycle the drilling riser in for full inspection on an approximate 5-year program when the joints are not in use. This would entail for traditional inspection, loading joints onto a boat, shipping to shore, unloading, removal of buoyancy, auxiliary lines, clamp bands, and sand blasting to remove coating. After completion of inspection and repair the reverse of the previous steps occurred to return the riser to the rig. A full inspection included visual of components, dimensional of

1 Copyright © 2003 by ASME

critical areas, thickness readings of pipe to monitor corrosion, and surface weld quality inspection. Pipe wall readings were taken with a slow handheld unit process. Weld quality inspections were completed by the use of a magnetic particle inspection, which only finds surface indications. SETTING THE STAGE A need for a full marine riser inspection on the rig was evident by numerous factors. These included; costly shipment and disassembly/assembly, epoxy coating being replaced by new thermal spray pipe coating (that is billed to last the life of the riser), and the more common remote overseas well locations that are not supported by a riser ready shore base. The only lacking components of a full rig riser inspection were the ability to inspect pipe wall thickness and welds from the interior of the pipe. All other aspects of inspection could and have been completed on the rigs. TOOL DEVELOPMENT ABB Vetco Gray Inc., a leader in marine riser design and inspection, and Global Automated Systems, a leader in automated non-destructive examination systems, have joined together to develop a fully mobile riser inspection program. The task was to utilize ultrasonic examination as applied by robotic tools that could easily be operated in remote rig locations. Two different RADAR tools were invented. This system offers the industry a safe, economical, and effective means to inspect marine riser without assembly. Prior to beginning field operations, the RADAR system was subjected to a full qualification program. During the testing process a total of 22 indications were implanted into the test samples. Both 21” x .625” wall and 5” x 1” wall samples were tested. On these samples the wall thickness results were measured within +/- .001” accuracy while the weld quality test indications were within +/- .039”. The accuracy levels are in line with current proven ultrasonic non-destructive methods(such as handheld units) just utilized in a different application method.

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RADAR TOOL DETAILS Two different size tools were developed to inspect different size pipes; both tools are capable of the same functions. The large diameter tool (Fig. 1.) inspects the main tube of the riser that may range in inside diameter from 16” to 24”. The small diameter tool (Fig. 2.) is used to inspect the auxiliary lines that may range in inside diameter from 2” to 5”. The listed ranges are common sizes, however if required the inspected size range can easily be modified. Both tools perform three major operations, video recording of pipe, weld quality inspection and corrosion mapping (wall thickness measurement). The tools consist of a main body navigating through the pipe and a head assembly that rotates. Circumferential and linear travel is accurately tracked by the use of encoders mounted on the shaft of the head and one wheel shaft. The encoders are small electronic devices mounted to a shaft to accurately measure very small incremental angular movement. Electronic impulses are converted and sent to a computer to monitor relational movement. The video is captured by two color video cameras that are in line with recording devices to document any area required. The corrosion mapping is completed by the use of (4) ultrasonic pulse echo longitudinal wave transducers spaced at 90 degrees. Four readings are taken simultaneously and the head can be rotated to any angle to achieve as many thickness readings as needed in the circumferential direction. The weld quality inspection is completed by the use of two different ultrasonic methods. Two sets of transducer heads mounted 180 degrees apart utilize Time of Flight Diffraction (TOFD) to analyze the body of the weld, while two sets of transducer heads mounted 180 degrees apart

Figure 2. Small Diameter Inspection tool

Figure 1. Large Diameter Inspection tool

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utilize pulsed echo shear waves to analyze the root and cap. The two TOFD and pulsed echo shear waves are taken simultaneously as the head rotates 180 degrees giving a complete 360-degree scan picture output of the entire weld volume. This type of scan may also be used in other areas of the pipe if required. FIELD OPERATIONS The complete operation is easily portable to any location. Requirements for pipe inspection are; the two RADAR tools(small and large diameter tools), 110-volt generator, control unit, small volume low-pressure water source, computer, two video screens and a drive assembly for small diameter tool. Required for dimension inspection are the necessary micrometers. Required for the connector flaw detection is a magnetic particle yoke, which is powered by a generator. All the above equipment can be shipped in two 4 feet x 4 feet x 3 feet aluminum boxes. Since the system relies on ultrasonic energy traveling through the material, it is important that accurate calibration of the tool be obtained. In this regard, thickness calibrations are made on the actual tube to be inspected. The calibration is made utilizing the obtained velocity measurements and tracks the pipe outside diameter and inside diameter automatically. In addition, sensitivity levels are also a concern during weld evaluations. In this regard, a calibration standard is provided at the job site and the B-scan will detect any indication over a length of .031”. The frequency of calibration is done on each of the first ten joints and then reduced after readings have been verified. The scope of a full Level III inspection is broken into five sections; visual, dimensional, connector integrity, weld quality and pipe wall inspection. The visual includes; main tube connector seal areas, auxiliary line connectors and seal areas, and any overall observations of riser components. The dimensional inspection is completed of critical areas of main tube and auxiliary line connectors. The connector integrity is verified by use of magnetic particle inspection of main tube connectors and dye penetrant inspection of auxiliary line connector hard facing. The fully automated RADAR system is used to do the critical weld quality and pipe wall corrosion mapping operations. After calibration, the RADAR tool is installed into the riser. The connector to pipe weld is aligned with the transducers using the on-

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board video camera. The weld scan is completed and the tool moves to the center weld. The scan is completed and the last weld is completed in the same manner. The corrosion mapping consists of the wall readings being taken throughout the pipe interior. The RADAR tools are aligned on the connector to pipe weld and the predetermined circumferential datum. The tool travels along the pipe length and the head rotates as the readings are taken. The simple design of the tools limits possible problems or misreadings that may occur. However if excessive mud is caked inside the pipe that may cause an interruption in the ultrasonic sound progression. Mud can be kept to a minimum if the riser pipe is properly flushed upon retrieval. In first generation of the tool water build up inside of the pipe was not expected to be a problem. However even with the small amount of water that is emitted from the transducers, it would pocket in the sagging areas of the horizontally laid pipe. This caused electrical shorts in the small diameter tool. The second generation of the small diameter tool has been designed to be water proofed to prevent recurring problems. INSPECTION OUTPUTS The inspections are customized to suit particular customer requirements for output. Detailed electronic reports are issued at the completion of each inspection, which include visual findings, dimensional readings of critical areas, and connector flaw detection reports . A video recording is offered of the entire pipe interior. The weld quality reports show the 360-degree B-scan images of each weld and serve as permanent record of weld integrity. Corrosion mapping inspection reports can include as many possible readings of the pipe wall as required. Typically 75-foot risers joint will have 200 equally spaced readings but if required more than 50,000 equally spaced readings may be taken. The report is in a color-coded format with colors set at different thickness levels. This makes it very easy to see potential problem areas and track the pipe deterioration with respect to age. Also, with the use of the encoders on each of the tools, the location of each reading may be repeated each time inspection is undertaken.

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SUCESSES To date, the RADAR riser tools have successfully inspected over 110,00 feet of riser pipe. Most notably was the full inspection of over 140 riser joints on a rig in transit between well locations in 16 days. TREND ANALYSIS AND RISK MANAGEMENT Relative to conventional inspections the mobile robotic unit allows for many times more data acquisition in much less time. When in the past 48 wall readings were taken in a 50-foot joint now 480 readings of that joint may be taken in the same time. With all the readings a 3-D wear model can be generated. Using the reports in a database format, wear progressions can be tracked for all aspects. This may include main tube connectors, auxiliary line connectors, as well as pipe wall thickness. Knowing the history of each joint can allow for statistical predictions which will assist the contractor in planning the repair cost, the scope and timing of the repairs, prediction of out of service time, and assist in maximizing the riser life. Most importantly marginal riser can be removed from service and minimize costly unplanned repairs and downtime. Figure 3 demonstrates an example inspection failure trend of one of the riser components, the main tube. Based on historical data this chart can help predict the percentage of main tube riser pipe that will have below acceptable wall readings related to the age of the riser. The small cross bars represent the margin of error for the given percentage.

Main Tube Inspection Failure Trend

0.00% 2.22%

10.17%

3.17%

0.0%

2.5%

5.0%

7.5%

10.0%

12.5%

0 to 9 10 to 14 15 to 19 Overall

Years Riser In Service

Chan

ce o

f Not

Pas

sing

Figure3. Inspection failure trend report

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CONCLUSION The RADAR system now offers to the industry a safe, economical, efficient alternative to complete the required inspection of all marine drilling riser systems. As the system is portable, it can operate on the rig or in the most remote job site while still providing very detailed reporting on the fit for function of the riser system. As the search for hydrocarbons continues to push deeper and into more harsh operating environments, advanced inspection systems like RADAR will provide the best insurance against unforeseen situations, which must be avoided. REFERENCES [1] Serta, O.B., Longo, C.E., Roveri, F.E., “Riser Systems for Deep and Ultra-Deepwaters”, OTC 13185, Houston, May 2001. [2] Avallone, E.A., Baumeister III, T., 1996 Mark’s Standard Handbook for Mechanical Engineers, 10th ed., McGraw Hill. [3] Shigley, J.E. 1989, Mechanical Engineering Design, 5th ed., McGraw Hill. [4] Kiemele, M.J., Schmidt, S.R., Berdine, R.J., 1990, Basic Statistics, Tools for Continuous Improvement, 4th ed., Air Academy Press.

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