Underwater Technology

Deepwater and Intervention Technology

by J. H. NIXON* and I. M. RICHARDSON*t

Abstract by SubSea International (OTTO, [1]), Comex (THOR Within the next few years, the offshore oil industry 1 and 2, [2]) and Statoil (PRS, [3]), they have many will be seeking to exploit hydrocarbon reserves at similarities. All use so me form of tractor, controlled depths inaccessible to saturation divers, and at which from the surface, crawling round a track installed the welding processes currently in offshore use will not on the pipe, and upon which is mounted a welding operate. Alternative processes exist for the water depth torch and manipulator, consumable feed unit, and range 500 to 1000 met res, and these have been shown weId pool viewing system. All utilise the GT A welding to be viable in laboratory trials. Further work is process; with filler addition. The task of the saturation required to bring them to full operational status, and diver is to install and remove these systems, and to to integrate them with the wide range of other equip- replace consumable spools and tungsten as ment required to carry out a complete underwater required. Such systems have been used for the past fabrication procedure without diver intervention. ten years, generally successfully, and are currently Although alternative fabrication techniques exist, it is being considered for operations at shallower depths, generally agreed that if hyperbaric welding can be and for an increasingly wide range of pipeline materials shown to be reliable, and to produce acceptable joints, [4]. it will continue to be used by the offshore industry. Although the pace of development of offshore At present, no facilities exist for hyperbaric welding hydrocarbon reserves has been irregular, and greatly research at depths significantly greater than 1000 influenced by the low price of crude oil, it is generally metres. Cranfield is currently commissioning a 250 bar agreed within the industry that significant reserves research facility, which can be used for undertaking exist in areas where the seabed is at water depths of studies into the performance and properties of arc 1 km and greater [5], and that these will be exploited welding at equivalent to a water depth of during the early years of the next century. In order to 2.5 km. accomplish this, however, it will be necessary to modify underwater welding practice greatly. Once one considers welding operations at depths t. Introduction significantly greater than 500 m, two problems occur. In general, most of the fabrication and repair of It is generally recognised that the viable limit for underwater pipelines takes place in Continental Shelf must be in the 500 to 750 m depth water depths, which are usually less than 200 metres. region. The increasing effects of high press ure nervous For these situations, manual welding techniques are syndrome (HPNS), and the extensive used, with gas tungsten (GT AW) for root times required, make deep saturation diving progress- welds and hot passes, shielded metal arc welding ively less attractive as depth increases. Additional data (SMA W) being employed to fill the bulk of the on the long-term effects of , wh ich have weid. led the Norwegian Government to declare operations In the early 1980s, a requirement arose to provide at depths greater than 180 m as especially hazardous, arepair capability for pipelines being laid across the only strengthen this argument (see Table 1, [3]). Norwegian Trench, an area of the North Sea in which In addition, welding process research has shown the water depth can approach 400 metres. It was appreciated that the physical capabilities of saturation Table 1 Depth ranges for diving and welding divers became more limited as depth increased, and Depth msw Diving Welding welding, as a skill requiring long term dexterity and , was particularly vulnerable to this 50 Limit for air diving Manual effect. It seemed unlikely that conventional manual welding welding techniques would produce consistently accept- 180 Norwegian operations able results at the increased depth of the Norwegian limit Trench. 300 Mixed gas saturation For the relatively simple weid geometries required diving GTAW to join pipes, automated orbital welding systems were 400 orbital systems developed. Although several of these exist, developed Limit for 500 saturation *The Marille Techllology Celltre, Cralljield University, diving Limit of GTAW Cralljield, Bedfordshire, MK43 OAL, UK 600 t This paper was presented at all SU T cOllference, SU BTECH Diverless GMAW '95, held 7-9 November 1995, Aberdeen. Proceedings are systems plasma 1000 available.from SUT. (Report Q{meeting Oll p. 28.)

3 Volume 21 Number 3 UndcrII'lItcr Tcchnology

that the GT AWare beeomes progressively less stable 3. Alternatives to are welding for deepwater operations as the environmental is inereased, and at If arc welding is not used as the pipe joining technique, about 500 m deep, it will become unacceptably a number of alternatives exist. Several varieties of unstable for operational use. The exact depth will mechanical connector have been developed for trans- depend on a variety of factors, such as the operating mission pipelines, and although bulky and expensive, eurrent, shielding gas composition and weid prepar- could be utilised in deepwater situations. Being purely ation geometry [6]. Shielded metal are welding is not mechanical, their operation is little affected by water espeeially suitable for robotie operation, because of depth. Recent studies have suggested that for maximum thc high lcvels of manipulative dexterity required, and reliability, metal to metal sealing techniques, based on the low metal deposition rate [7]. cold forging technology, should be used [3]. Thus, at depths greater than about 500 m, both the Alternatively, a solid phase welding technique, such capability for diver intervention, and the welding as explosive welding (highenergy bonding) could be processes with which the offshore industry has the used. A complete HEB pipe joining system was most experience, w.illcease to be operable. Alternatives developed by British Underwater Pipelines Engineer- to arc welded fabrieation techniques exist, such as solid ing, of Barrow in Furness, in the late 1970s. This phase welding, mechanical connectors, grouting, and consisted of aseries of engineering packages, deployed the like. However, a general consensus within the by submersible, to cut pipes, remove the weightcoat, industry suggests that if arc welding ean be shown to and prepare the surface of the pipe for bonding. bc viable, it will continue to be used, because of its Although only capable of lap configuration joints, the high joint effieiency, low and good operational system was shown to be feasible [10]. The development record. Because of the high probability that so me form of effective arc welding techniques, possibly combined of subsca completion will be used in these water with reservations concerning the use of explosives depths, welding system development to date has adjacent to offshore structures, and the inspection of concentrated on pipeline joining systems, with their the solid phase welds, inhibited further development, simpler and more predictable weid geometry. but the technology could be revived for deepwater operations. Although more speculative, the use of high perform- 2. Non-wclding deepwater intervention teehnology ance adhesive joining techniques might be considered Thc Norwegian objeetive, of minimising all diving for deepwater situations. Adhesives are now utilised operations at depths greater than 180 m, has resulted in many demanding applications, such as the fabrication in an EU R EKA research programme to upgrade the of automotive and aerospace components, and although engineering specification of current diver-deployed the cost of such adhesives is high, the quantities orbital welding systems to enable them to operate required would be relatively smal!. Tt may be that a witllOut diver assistance [8]. Because mechanical hybrid joining technique, using adhesives to enhance systems are relatively depth insensitive, this pro- the performance of a mechanical connector, might gramme will provide valuable experience for the prove effective in these situations. construction of welding systems to operate at greater depths, provided it can be demonstrated that effective 4. Are welding technology for depths of 500 to 1000 m welding processes are available. Over the past few years, research into hyperbaric Even when conducting underwater welding oper- welding technology in the depth range 500 to 1000 m ations, the vast majority of underwater activity is not has been carried out at several research organisations, directly concerned with the welding process. For a principally GKSS and the Universität der Bundeswehr typical pipeline repair operation, the pipe must be in Germany, STNTEF in Norway, and Cranfield located and the worksite surveyed to ensure that the repair equipment can be safely deployed. It may be necessary to uneover buried pipe, or to lift the line sufliciently to permit full equipment access. Any wcightcoat or protectivc covcring must then bc rcmovcd, and thc pipc c\caned and prepared, usually by machining, for the welding operation. Aftcr welding is complete, the weld must be inspected, so me form of protection applied, the equipment recovered to thc surface, and the worksite restored to its former status. Fully diverless intervention procedures will require the development of equipment to carry out all of these tasks, with sufficient adaptability to accommodate the variability commonly encountered in underwater operations. Eq uipment of this type will be required whatever joining technique is used for underwater pipelines, and is best developed by the underwater engineering industry, drawing on thcir"experience of current repair systems [9]. FiiJ.} Cross secrir)/] o{ a plasma weid made a1 100 haI'

Winler 1995-96 4 Vnderwater Technology

University in England. Although these programmes process were not suitable for offshore use. However, differ in detail, the overall consensus is that two arc the closely allied f1ux cored are welding process welding processes can be effectively opera ted in this (FCA W), using a tubular configuration , was depth range-plasma welding and gas metal arc successfully used in hyperbaric environments [16]. welding (GMA W). The commercial availability of high performance Plasma welding is a derivative of GT AW in which e1ectronieally controlled welding power supplies has the are, instead of being allowed to spread freely, is Ied to are-evaluation of the process [17], and the constricted within a water cooled orifice [11]. This development, by G KSS [18] and Cranfield [19], in reduces the cross-sectional area of the are, increasing separate programmes, of special arc and stability. A significant problem control systems for hyperbaric GMA W. These units, with plasma welding is that the performance of the wh ich are similar in general eoncept although they are is influenced by a large number of variables, differ in detail, control the static and dynamic output including the internal geometry of the welding toreh, characteristics of the welding power supply in order Cranfield has recently completed a major research to optimise the stability of the GMA welding pro- programme into hyperbaric plasma welding, and has cess. Using such control systems in conjunetion with demonstrated that the plasma are remains stable to high performance welding power supplies, GM AW press ures equivalent to 1000 m water depth, and can has been shown to be capable of all positional be sueeessfully and reliably initiated at that pressure operation, with acceptable stability and fusion levels, [12]. at pressures equivalent to more than 1000 m water In surfaee welding, plasma ares are used in two depth [20]. ways. Ir operated with relatively large diameter Although special power supply eontrol systems are eonstrietions and minimal setback of the tungsten necessary for deepwater hyperbarie GMA welding, orifiee behind the eonstrietion, they perform similarly these do not add significantly to the cost of the welding to GT AWares, but are more stable [13]. Typieally, system, and standard high performance welding power a plasma are opera ted in this way will develop an supplies can be used to supply the aetual welding are voltage about 10% higher than that of a free- eurrent. The process has been shown to be feasible, burning arc in similar conditions. Ares of this type but more research is required to develop effective have been used, in eonjunetion with a eonsumable feed torch manipulation and joint filling strategies for system, to produee test welds at pressures as high practical weid geometries. The process also currently as 100 bar, equivalent to 1000 m water depth (see develops significant amounts of welding fume, and Figure I, [11 J), other welding variables such as the shielding gas When welding at one atmosphere, if the power composition remain to be optimised. Industry in density of the plasma are is inereased, by redueing general has considerable experience using GMAW in orifiee diameter, increasing eleetrode setback, and robotic welding applieations, and the proeess may be inereasing plasma gas f1ow, it is possible for the are appropriate if similar robots are used within hyperbaric to operate in the 'keyhole' mode, producing weid workchambers, has been suggested [8, 21]. beads whieh are much deeper than they are wide. Until The current state of hyperbarie arc welding is reeently it was thought that keyhole welding was not therefore that operational systems and procedures possible under hyperbaric eonditions, but reeent work exist which are capable of operating 'to depths of about at Cranfield [12J and the Universität der Bundeswehr 500 m. In the depths of 500-1000 m, laboratory [14J in Hamburg have produeed keyhole welds at research programmes have demonstrated that at least press ures equivalent to depths greater than 300 m, and two are welding processes are eapable of stable and developments eontinue. Uthis teehnique can be shown eonsistent operation, although only preliminary work to be operationally feasible, it may have important has been earried out to investigate the meehanical and conseqllences for the root welding of pipelines, as it metallurgical properties of welds made using these enables high integrity welds to be carried out mueh teehniques. If these prove to be aeeeptable, it should faster than by other teehniqlles. A significant problem be possible to produce a deep water pipe repair system with such ares is that the operating voltage required by utilising this welding teehnology and adapting the is very high, and special welding power slIpplies have engineering faeilities developed within the EUREKA been developed for this application [15]. programme for greater depth eapability. As a welding proeess, plasma is closely related to Thus it can be seen that the development of hyper- gas tungsten are welding, and it is likely that eurrent baric welding technology is a multi-stage process. For GT AW welding systems eould be modified to operate any given depth, welding process feasibility trials the process, Some new operating procedures would are necessary to establish the viability of welding be required, such as an are initiation programme, but teehniques. Then, more detailed proeess optimisa- many other systems would be eompatible, Such a tion studies are required to determine the effect on modification would be the simplest way in which to the proeess of major operating variables, such as increase the depth capability of current automated the eharacteristies of the welding power supply, the welding systems. eomposition and f10w rate of shielding gas, and the was originally evaluated for welding toreh manipulation strategy. The objeetive of hyperbarie applieations in the mid 1970s, when it was this stage of the research is to maxi mise the stability determined that the low fusion levels produeed by the and consisteney of the proeess, aeross as wide a

5 Volume 21 Number 3 Underwaler Technology

1996 [22]. This will initially carry out the process feasibility studies described above, probably in the depth range 1000 to 1500 m, and will be extended to greater depths as results permit. Tnitially, the welding trials will be carried out on flat plate material in all welding positions, for convenience in weid evaluation, but the system has been designed to permit the installation of an orbital welding system at a later date.

References 1. Lyons, R. S. & Middleton, T. B. 1984. Orbital TTG system simplifies underwater welding. M etal Construction, October. 2. Blight, J. & Baylot, M. 1987. THOR-2 diverless welding system. Proceedings of the 2nd Inter- national Conference on Developments in Auto- Fiy.:? T"~ ]50 I){II' pr~SSI/I'~ l'~ss~1 (/1 Cl'((/!fi~/d mated and Robotic Welding, London, November. 3. Styve, K. & Andersen, K. ]994. Hyperbaric pipelines re pair system: current achievements and range as possible of operating conditions. It is then new deepwater challenges. Proceedings of OPT necessary to establish that welds produced by the '94 Offshore Pipeline Technology Conference, technique, on typical offshore specification materials, Oslo, February. have acceptable mechanical and metallurgical prop- 4. Malone, R. B. & Ra]ston, J. D. ]992. Hyperbaric erties. Only then can operational welding systems and welding of exotic steel pipeline. Proceedings of the procedures be specified. 11th International Conference on Offshore Mech- In order to continue this development process for anics and Arctic Engineering, Calgary, lune. water depths in excess of 1000 m, experimental 5. LeBianc, L. 1995. Abyssal hydrocarbons off West facilities are required with appropriate operating Africa indicate widespread potential. Offshore pressure capability. Cranfield is currently commission- (incorporating The Oi/man), March. ing HyperWeid 250, a new hyperbaric welding 6. Hoffmeister, H. ]984. Deep underwater welding- research facility capable of operating at a maximum session report. Proceedings of the International pressure of 250 bar, equivalent to 2.5 km water depth. Workshop on Quality in the Underwater Welding The system has been constructed by means of funding ofMarine Structures, Colorado, USA, November. from the Engineering and Physical Sciences Research 7. Nixon, 1. H. 1986. The application of ROVs to Council (EPSRC), acting through the Marine underwater welding repair tasks. Proceedings of Technology Directorate Ltd. Tt is believed that this is the ROV '86 Conference, Aberdeen, lune. the highest pressure dedicated welding reseach facility 8. Gibson, D. 1994. Achieving diverless repair of in the world at present. pipelines and other subsea equipment in hyperbaric Descri bed in more detail elsewhere [15] the new environments. Proceedings of DEEPTEC'94, system draws on the experience of over 20 years Aberdeen, April. hyperbaric welding research at Cranfield. The pressure 9. Hutt, G. & Pachniuk, I. 1993. Trends in diverlessl vessel and gas supply system were specified by remotely controlled hyperbaric pipeline tie-ins. Cranfield, with detail design and construction by Proceedings of the Third InternationalOffshore Stansted Fluid Power Ltd (see Figure 2). The welding and Polar Engineering Conference, Singapore. power supply system was designed in conjunction with 10. Redshaw, P. R., Stalker, A. W. & Allen, K. 1978. Fronius Schweissmaschinen, of Austria, and can Explosive welding-the deepwater pipeline con- suppty 500 amps at over 200 volts, with an additional nection/repair . Proceedings of the 10th 50 amp supply capable of700 volts output. The overall Annual Offshore Technology Conference, Houston, facility control system is being developed in conjunction USA, May. with Isotek Ltd, who are major suppliers of control 11. Richardson, I. M. 1994. Hyperbaric plasma systems for operational hyperbaric welding systems, welding. Offshore Research Focus, December. such as PRS and THOR. This will simplify the transfer 12. Richardson, I. M. & Cave, W. F. 1994. Plasma of process and control technology from the research welding at press ures 1 to 100 bar. Final report to programme to operational use in the offshore industry. the Marine Technology Directorate Ltd. (EPSRC Additional design studies relating to are viewing Grant No. GR/G259] 7) December. systems, welding torches and data logging and analysis 13. Richardson, I. M. 1993. Deflection of a hyperbaric systems are also being undertaken. plasma arc in a trans verse magnetic field. Pro- Currently, a large, multi-sponsor Managed Pro- ceedings of the 12th International Conference on gramme of deepwater arc welding feasibility studies is Offshore Mechanics and Arctic Engineering, being formulated, and is scheduled to start early in Glasgow, lune.

Winter 1995-96 6 Underwater Technology

14. Hoffmeister, H. 1995. Private communication. properties at pressures 1 to 60 bar. Proceedings of 15. Nixon, J. H. & Richardson, 1. M. 1995. The design the 10th International Conference on Offshore and construction of a 250 bar hyperbaric welding Mechanics and Arctic Engineering, Stavanger, research facility. Proceedings of the 14th Inter- June. national Conference on Offshore Mechanics and 20. Dos San tos, J. F., Szelagowski, P., Schafstall, Arctic Engineering, Copenhagen, June. H. G. & Hensen, D. 1988. Mechanical and 16. Lythall, D. J. & Pinfold, B. E. 1977. New under- metallurgical properties of robotic underwater water welding process proved for continental shelf welds performed within a depth range of 100 to depths. Proceedings of the 9th Annual Offshore 1100 msw. Proceedings of the 7th International Technology Conference, Houston, May. Conference on Offshore Mechanics and Arctic 17. Richardson, 1. M. & Nixon, J. H. 1985. Open are Engineering, Houston, USA, February. pulsed current GMAW: application to hyperbaric 21. Boyle, B. G., McMaster, R. S. & Nixon, J. H. 1995. welding operations. Proceedings of the ASM Teleoperation of an underwater robotic repair International Conference, Toronto, October. system using graphical simulation. Proceedings of 18. Dos San tos, J. F., Szelagowski, P., Schafstall, H. G. a Colloquium on Control of Remotely Operated & Dobernowsky, A. t 990. Preliminary investi- Systems: Teleassistance and Teleoperation, organ- gations of the effect of short circuit variables on ised by the Institution of Electrical Engineers, metal transfer above 60 bar abs. Proceedings of London, May. the 22nd Annual Offshore Technology Conference, 22. Billingham, J., Nixon, J. H. & Richardson, l. M. Houston, May. 1995. Programme in deepwater hyperbaric welding. 19. Hansen, H. R., Rassmussen, A. & Richardson, Published by the Marine Technology Centre, 1. M. 1991. Hyperbaric GMA process control and Cranfield University. NEW BOOK from SUT CONTENTS Keynote Addresses: The Subsea Business SUBTECH'95 Revolution-Sink or Swim for Offshore Contracting, R. 5hepherd; R D & D in the Market of the Millennium; K. Addressing the Subsea Challenge Bassiti; Dangerous Encounters: Safety to Installations and Fishing Gear, K. Knox & A. G. Hopper. Session One- held in Aberdeen, 7-9 November 1995 Subsea Roboties: Inspection of Subsea Nodal Welds by the co-sponsored by IMCA ARM Robot Manipulator, D. R. Broome, T. J. Larkum & M. 5. Hall; The TUUV Program, 1. Edwards; An AUV for PROCEEDINGS NOW AVAILABLE Pipeline Survey- The Next Step in Low Cost Remote price i40.00 Ci36.00 to members) Operations Technology, J. Gooder & A. Tonge; Unmanned Mini-Submarine for Offshore Inspections, A. Bjerrum, B. These proceedings of the 5UBTECH '95 Conference Krogh & L. Henriksen. Session Two-Deepwater address the needs of the subsea and intervention indus- Developments: Deepwater Welding and Intervention try in a time of financial and physical challenges, with Technology, J. H. Nixon & I. M. Richardson. Session continuing low oil prices and a need to develop small Three- Teehnical Developments: SnapLay-A Modular and deepwater fields economically. The resulting new Pipelay Technique, M. Craig & M. Dick; Remote Low Cost technologies include improved designs and the use of Subsea Control System, P. Hands; Back to Basics-The new and alternative materials to help reduce the burden Economically Alternative Tree Design, A. C. Dyson & J. C. of routine inspection and maintenance costs, and im- Cullion; The Next 5 Years, M. Witton; Integrated Subsea proved operating procedures to reduce costs. Production Surveillance: Sensors for Subsea Production As weIl as subsea engineering design, submersibles Systems, E. L. E. Kluth; Detecting Freespans in Sidescan have evolved dramatically from increasingly sophisti- Records-Automatically, C. 5t J. Reid & A. D. Tress; cated unmanned, but tethered, vehicles in the eighties, Horizon 2000: A Novel System Approach to Inspection and with the future leaning towards the development of Integrity Monitoring of Flexible Flowlines and Risers, B. G. autonomous vehicles. At the same time, the industry Redden .Session Four-Diving and Physiology: Testing has developed an impressive array of tools to meet the Communications Systems on Diving Installations, V. Flook; complexities of subsea tasks, and further innovations The IMCA-HSE-UKOOA Dive Data Management System that will be needed for operations in deeper and more (DDMS),J. c.Gardiner& 5. T. Brooke;NoiseHazard in the difficult water. Diving Environment, J. Nedwell & K. Needham; Aimed at engineers, designers and operators, these Development of Cyclops- A Diver' s Heimet Display System proceedings describe how the ind ustry is rising to meet for Offshore Inspection and Maintenance Operations, A. G. these challenges in sessions on Subsea Robotics, Deepwater Robinson & N. Wright. Session Five-Operational Developments, Diving and Physiology and Operational Experienee: Operational Experience ofMultipass and Backfill Experience. Ploughs, J. B. Machin; Work Class ROVs: What are the Performance Limits and How Can They Be Extended? H. W. Orders (VISA and Mastercard accepted) should be Williams; Towards ROV-less Installation: Experience Gained sent to: The Publications Office, SUT Head Office, on BP Cyrus, I. Edwards; Fulmar SALM Buoy Removal- 76 Mark Lane, London EC3R 7JN, UK. Tel: +44(0)171 An Application ofCold Cutting, A. West & A. G. Counsell; 481 0750, fax: +44(0)1714814001. Cold Cutting for Decommissioning, T. Copros.

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