DIVERLESS SUBSEA HOT TAPPING OF PRODUCTION PIPELINES Dale Calkins Senior Project Engineer, TD Williamson Inc Biography Dale Calkins joined TD Williamson Inc in November of 1999 after working as a consulting engineer for about ten years providing design services to a variety of oil related equipment manufacturers. In 1977 Dale received a Bachelors of Science Degree from the University of Houston in Mechanical Engineering and went to work for National Supply Company in Houston, Texas where he designed valves and actuators for surface and subsea applications. Starting in 1984, Dale went to work for the Petroleum Equipment division of FMC Corporation and continued to design valves and related equipment. He completed a Masters of Arts degree in Economics in 1991. Mr Calkins is a registered professional engineer in both Texas and Oklahoma and a senior member of the Society of Manufacturing Engineers. He is also a member of the American Society of Mechanical Engineers in which he has actively served in a number of capacities. He is currently vice chairman of membership/member interest for the Mid- Continent section of ASME. Abstract A number of hydrocarbon transmission pipelines are presently located below water in the Gulf of Mexico and other offshore locations to facilitate transportation of product from wells to storage locations onshore. The cost of laying this pipeline on the ocean bottom is staggering. As exploration and production moves to yet deeper water, how to economically transport this new product will become a key factor in determining a well s profitability. A technical alliance has been formed to develop the necessary equipment and processes to tie new fields into existing production lines without stopping the flow of product. Timing of new developments is such that production drops may coincide with the need for transporting product from new fields. In order to tie into an existing pipeline it is necessary to find a suitable location. The pipeline must be relatively level and any concrete coating must be removed. The pipeline must then be inspected for any imperfections or out of round condition. After a suitable location has been determined, the pipeline will be lifted so a wrap around fitting can be installed. A valve will be attached to this fitting that seals around the pipe so that the tapping machine can drill through the fitting and into the pipeline with the valve open. After the drilling operation has been completed, the cutter will be retracted and the valve closed so the tapping machine can be removed. Now that the hole in the pipeline has been drilled and the tapping machine removed, a pipeline from the new well can be connected to the fitting on the existing pipeline; all without interrupting the production from the older well. TD Williamson has manufactured subsea drilling machines for a number of years now. The unique aspect of this alliance is that all operations are performed without the assistance of divers. This aspect makes the technology practical for water depths as low as 10,000 feet below the surface. This paper will concentrate on the technical aspects necessary to adapt the drilling machine for diverless operation in deep water. These include the following: a. Computer control system adapted for diverless operation. b. Boring bar position information. c. Boring bar speed and feed information. d. Pressure balancing compensators adapted for higher internal/external pressures. e. Positive coupon latching mechanism. f. Enhanced hydraulic system for failsafe operation.
DIVERLESS SUBSEA HOT TAPPING OF PRODUCTION PIPELINES Dale Calkins Senior Project Engineer, TD Williamson Inc Introduction Many hydrocarbon transmission pipelines are located in the Gulf of Mexico and other offshore areas to transport product from subsea wells to storage locations onshore. The cost of laying these pipelines on the ocean bottom is staggering, especially in deep water. As exploration and production moves to yet deeper water, transporting the new gas and oil economically will become a key factor in determining a well s profitability. The product transportation issue may be influenced by the timing of new field start up and the production decline in older fields. As production drops from older wells, sufficient capacity may become available in existing transmission lines to handle production from the new fields. This would reduce the need for constructing all new transmission lines. However, it will require new technology to tie these deep, new fields into existing production lines without stopping product flow. Several energy-related companies have formed a technical alliance to develop the needed equipment and processes for these deep-water tie-ins. One of those essential procedures is hot tapping. Hot tapping is the process of making a new connection in a pipe by drilling or tapping a hole in the pipe without stopping fluid from flowing through the pipeline. TD Williamson, Inc. (TDW) has manufactured hot tapping equipment since the 1950s and has provided tapping machines suitable for subsea operation for a number of years now. TDW is part of the technical alliance addressing the deep sea piping issue. The other alliance members also have significant experience in subsea operations. The unique aspect of the technology being developed by the alliance is that all operations are performed without divers. This aspect makes the technology practical for water depths as deep as 10,000 feet below the surface. This paper will concentrate on the technical developments necessary to adapt hot tapping machines for diverless operation in deep water. In order to tie into an existing pipeline it is necessary to find a suitable location. The pipeline must be relatively level and any concrete coating must be removed. The pipeline must then be inspected for any imperfections or out-of-round condition. After a suitable location has been determined, the pipeline will be lifted so that a subsea hot tap fitting can be installed. The subsea hot tap fitting is designed to seal around the pipe and provide an outlet and valve to which the new pipeline will be connected. The tapping machine will drill through the fitting and into the pipeline with the valve open. However, to make up the connections without divers, a special connector is required between the valve and the tapping machine. This two piece collet connector has a female half connected to the hot tap fitting and a male half connected to the tapping machine. After the tapping operation has been completed, the cutter will be retracted and the valve closed so that the tapping machine can be removed. Once the tap is made and the tapping machine has been removed, a pipeline from a new well can be connected to the fitting on the existing pipeline. All these operations are performed without interrupting the production from the older well.
Tapping Machine Design To maximize user control, the tapping machine has independent feed and drive control. Drive is the rotational speed of the cutter, usually measured in revolutions per minute (RPM). Feed is the cutter's rate of advance toward the pipe, usually measured in thousandths of an inch per revolution of the cutter. To obtain independent control, two hydraulic motors are used in the tapping machine. The drive motor rotates the drive tube which is keyed to the boring bar. The feed motor rotates the feedscrew which is threaded and turns in the feednut that is press fitted to the boring bar. The cutter and pilot drill are attached to the boring bar with a cutter holder. Each motor is controlled by an hydraulic directional proportional valve. To measure the drive and feed RPM the diverless tapping machine is equipped with Hall effect sensors. Rotating magnet wheels are mounted behind the feed and drive motors. The Hall effect sensors detect passage of the magnets to provide rotational speed data of the motors. By making use of the known relationship between RPM and advance of the boring bar toward the pipe, the feed rate can be calculated. The feedscrew is manufactured with four threads per inch. Right hand rotation of the drive motor advances the boring bar toward the pipe while right hand rotation of the feed motor retracts the boring bar away from the pipe. Using this relationship the feed rate is calculated after subtracting the feed motor RPM from the drive motor RPM. Note that an anti-stall feature is also available. If the cutter starts to stall, the feed motor RPM will exceed the drive motor RPM and the cutter will be retracted away from the pipe to clear the cutter. In addition to the Hall effect sensors derived position, a more direct indication of position is available with a magnetostrictive linear position transducer. The motor configuration has a through shaft which permits use of this transducer for position indication. Magnetostrictive technology uses the tendency of some materials to change shape during exposure to a magnetic field. A permanent magnet moves along a magnetostrictive wave guide as the boring bar extends or retracts. The sensor periodically produces an electromagnetic pulse along the wave guide. The pulse creates an interaction between the two magnetic fields. Position is determined by measuring the elapsed time between application of a current pulse and reading of the resulting strain pulse. This provides a highly repeatable result with no moving parts so that no wear occurs. The motors are enclosed in an oil filled housing to prevent ingress of seawater. This housing is equalized to the pressure at the subsea water depth as is the hydraulic fluid used to operate the motors. Check and relief valves are used to assure that no significant pressure differential can occur even if the compensation system fails. The boring bar pressure is first equalized to the subsea pressure and after the pilot drill has penetrated the pipe, the boring bar pressure is equalized with the pipeline pressure. This equalization system significantly reduces the forces necessary to rotate the boring bar while tapping. A relief valve is also used here to ensure that the boring bar can be retracted after the tap in the event the equalization system fails. These equalization systems are achieved using piston accumulators. An accumulator system is required for the boring bar since fluid is being transferred from below the boring bar to above the boring bar as the cutter advances toward the pipe. The control panel for the tapping machine includes electronic controls for operating both motors as well as their RPM readouts. The linear position indication as well as position of the pistons in the compensation system are also monitored. Pressure readouts at key locations such as feed and drive motor input, boring bar accumulator, and motor housing are also available. The diverless tapping machine weighs approximately 7000 pounds completely assembled and filled with hydraulic oil. Overall length of the tapping machine is just over 15 feet when fitted with a cutter and pilot drill. Overall stroke of the boring bar is more than 80. The tapping machine is designed to make 6 to 24 taps into a variety of pipe diameters. The machine is equipped with an adapter flange about midway on the tapping machine outer body. Typically the cutter will be aligned with the bottom of the collet connector. The adapter will mate with the flange on the tapping machine body and adapt to the appropriate flange on the collet connector. The cutter and pilot drill will protrude into the collet connector just above the bottom of the male connector. This minimizes the travel required to begin the tap without exposing the cutter during subsea deployment of the tapping machine.
To stay on center when making a tap, a pilot drill is used to pierce the pipe first, then the cutter is guided by this drill. The pilot drill for this machine has increased reliability for coupon retention in its design. The coupon is the section of material removed from the pipe in the cutting operation. Retaining the coupon is important to prevent damage to downstream equipment or potential blocking of the pipeline. In addition to the field-proven U-wire design used on most TDW tapping machines, this pilot drill is equipped with positive-retention latches. High velocity gas flow can sometimes cause the coupon to shear a U-wire during retraction from the pipeline. These latches provide extra assurance of coupon retention in addition to the multiple U-wires used on this pilot drill design. The diverless tapping machine cutter uses hardfaced teeth. These are welded to the body of the cutter and then precision ground. This special hardfacing material has excellent toughness and ductility to minimize wear and eliminate the possibility of losing a tooth. Variations in pipe material and cutting stresses during the tap can be quite severe. Brazed insert style cutters do occasionally lose teeth, and if jammed in the pipe a lost tooth can strip the other teeth from the cutter. Hardfaced teeth virtually eliminate the possibility of having to replace the cutter during the middle of a tap. Another of the safety features of the diverless tapping machine is the mechanical override adapted for use by a remotely operated vehicle (ROV). If for some reason hydraulic power to the tapping machine is lost during subsea operation, the cutter can be retracted remotely using the ROV and then the tapping valve can be closed. After power is restored the tapping operation can be continued or the tapping machine can be retrieved if additional repairs are needed. In-House Testing Design and testing of the tapping machine has been conducted by making use of a number of test fixtures. A packing test fixture was used to determine optimum seal design. Frictional forces and heat build up exceeded expectations for the seals and a significant amount of research and testing went into deciding the best seals for this application. External pressure integrity of the proportional valves was initially verified in a small pressure vessel. The pilot drill design was optimized using a test setup that used a hydraulic cylinder to simulate retraction forces. In-house testing included torque testing, pressure testing, V-block testing and tapping under pressure. Torque testing involves applying a known load to the end of the boring bar. Through this process the tapping machine capacity can be determined. The diverless subsea tapping machine can supply a torque exceeding 3000 foot pounds. Pressure testing is performed at 4500 psi and tests the seals at the boring bar, drive tube, feedscrew, and pressure tube simultaneously. V-block testing is tapping through a piece of pipe mounted in a V-block fixture without any pressure in the pipe. To test the tapping machine s ability to cut through pressurized pipe, a 20 test fitting was designed. This fitting bolts to a spool piece and permits 20 pipe with end caps to be welded in the fitting for making the test taps. The diverless tapping machine is designed for internal pressures up to 3705 psi consistent with ANSI/ASME class 1500 fittings. The fitting and spool were designed to this internal pressure as well as an external pressure of 4500 psi to simulate subsea pressure at 10,000 feet below sea level. Hyperbaric Testing and Field Trial To test the tapping machine in conditions simulating operation at maximum subsea depth, arrangements are being made to install the machine - complete with the test fitting - in a hyperbaric chamber that can be pressured to 4500 psi. This hyperbaric chamber is available at a US Navy facility in Carderock, Maryland. The hyperbaric pressure chamber is 6 feet in diameter and more than 21 feet deep and can be pressured up to 6000 psi. This is a vertical vessel which will also simulate a vertical tap similar to what we will experience subsea. We will conduct two tests at this facility. We will first pressure the test fitting to 3705 psi with nitrogen gas and tap through the fitting with the hyperbaric chamber
unpressured. Then we will replace the fitting and pressure the hyperbaric chamber to 4500 psi with no pressure in the test fitting and tap through the fitting again. These two tests will simulate the two extremes for which the tapping machine has been designed. After successful completion of the hyperbaric testing, the diverless tapping machine will be assembled in Houston in conjunction with equipment from the other members of the alliance. Testing under pressure will be repeated with all the mating equipment at a surface facility. Offshore testing of the diverless tapping machine is now planned for spring of 2001.