jackup rig whitepape final lores spreads

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White Paper usa.siemens.com/ids Abstract This white paper provides a brief primer on what offshore jackup rigs are and how they operate. It then describes the benefits of using jacking systems consisting of Integrated Drive Systems with programmable logic controllers (PLCs), ruggedized gearboxes and variable speed drives (VSDs) for precise, real-time control of torque through ruggedized gearboxes to rack and pinion lifting mechanisms. An overview of two safety principles is provided: (1) platform leveling; and (2) layered, redundant jacking system architectures. The advanced age (20-30 years) of more than 60 percent of the world’s fleet of approximately 380 jackup rigs offers naval architects and maritime engineers the opportunity to incorporate greater safety in the jacking systems of new rigs. Integrated Drive Systems: Boosting jackup rig safety How tri-axis automatic leveling and a layered architecture can improve jacking system efficiency and safety

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Page 1: Jackup Rig Whitepape FINAL LoRes Spreads

White Paper

usa.siemens.com/ids

Abstract This white paper provides a brief primer on what offshore jackup rigs are and how they operate. It then describes the benefits of using jacking systems consisting of Integrated Drive Systems with programmable logic controllers (PLCs), ruggedized gearboxes and variable speed drives (VSDs) for precise, real-time control of torque through ruggedized gearboxes to rack and pinion lifting mechanisms. An

overview of two safety principles is provided: (1) platform leveling; and (2) layered, redundant jacking system architectures. The advanced age (20-30 years) of more than 60 percent of the world’s fleet of approximately 380 jackup rigs offers naval architects and maritime engineers the opportunity to incorporate greater safety in the jacking systems of new rigs.

Integrated Drive Systems: Boosting jackup rig safetyHow tri-axis automatic leveling and a layered architecture can improve

jacking system efficiency and safety

Page 2: Jackup Rig Whitepape FINAL LoRes Spreads

Offshore jackup rigs are the oil and gas industry’s drilling technology of choice in the world’s ocean depths up to 550 feet. They make up about 60 percent of all offshore drilling platforms, the rest being semi-submersibles and drill ships. However, because more than 60 percent of today’s fleet of approximately 380 operational jackup rigs is 20 years or older, the demand for new jackup rigs is growing.1 As orders for new ones are being prepared, now is a good time for owners, operators and naval architects to consider the extra safety benefits of tri-axis leveling and redundant, multilayer jacking system architectures.

Background primer For readers unfamiliar with the workings of jackup rigs, the following background should help. In brief, jackup rigs are massive, hull-based legged structures. Their hulls can be triangular, square or rectangular in shape, with deck areas of up to 1.5 acres or larger and drilling deck loads of 15,000 kilopounds (kips) or more. Hulls provide space for mechanicals, supply storage and living quarters.

Depending on its platform shape, a jackup rig can have three, four or six legs, but most have no more than four, with three legs predominant among today’s newer rigs and arranged around the hull’s perimeter in a triangle pattern. Legs of a jack-up platform can be up to 700 feet or more in height to enable its platform to be elevated up to 100 feet above the ocean surface, above the wave heights of all but the most severe storms.

The legs may be cylindrical or trussed, with the latter used in deeper waters and newer jackup rig designs. Trussed legs are built with corners of vertical tubing called chords that provide axial and structural rigidity, while braces provide shear resistance. The legs can have three or four chords and use X-shaped or newer K-shaped bracing. Compared to cylindrical legs, trussed legs are lighter and have less wind drag, which is especially critical during towing operations when the legs are raised. During this time, the legs extend into the air and create inherent vessel instability because of the higher vertical center of gravity that their height creates.

Straightforward operation Large and as complex as jackup rigs are, their operating principle is simple: The legs are retracted while the watertight hull is towed into place, then lowered into the water until they contact the sea floor. Next their large, discus-shaped footings—called spud cans, with sloping tops and bottoms—are secured in the seabed by pre-loading the rig’s weight with ballast water in the hull. Then the jacking process continues, elevating the hull until it reaches its specified working height above the water. At that point, brakes are applied, rack chocks are engaged and drilling operations can begin.

All jackup rigs today used in deeper waters have legs that use a rack and pinion system, which allows for continuous jacking operations. Leg movement is controlled electrically via motors with soft starters, variable speed drives (VSDs) or hydraulic-operated lifts. The latter has many drawbacks, including

To ensure the safety of personnel and equipment on jackup rigs, it’s critical to keep the platform level during jacking operations, which is the raising or lowering of the hull after the legs are secure on the seabed.

Two out-of-level conditions can exist. One occurs within a leg itself, when one of its chords is out of phase with the others, much like standing sideways on a hill, which makes one leg lower than the other. This is called rack phase differential (RPD). Simply put, RPD occurs when a rack running vertically along the length of either side of a leg’s chord gets out of phase with racks on a leg’s other chords. This condition can damage the other legs by causing excessive bending and stress in them, which in turn can lead to a possible catastrophic capsizing of the rig. RPD can also overload the jacking system’s components, which may not lead to their failure but could damage them until they need repair or replacement.

Another out-of-level condition can occur during jacking operations as one or more of the rig’s legs might start to sink slowly deeper into the sea floor. The corner or corners of the platform supported by that leg or legs will become lower than the other(s), creating increasing amounts of structural and metallurgical stress as weight loads shift. Some other causes of an out-of-level condition while jacking can be:

• One or more legs has unexpectedly punched through the sea floor;

• A spud-can slipped into a sea floor depression;• Errors in speed commands received by lower quality VSDs

due to signal interference; • Differences in the slip characteristics of the induction motors;• Unequal torque distribution resulting in not all of the shaft

torque is contributing to vertical leg movement;• Unequal guide friction.

complicated and labor-intensive assembly, noise, energy inefficiency, filtration requirements, fire and explosion hazards if leaks occur, and environmental problems due to possible leaks. Direct Online (DOL) electrically driven jacking systems are typically less accurate, require mechanical overdesign and have more wear-and-tear on pinions and racks.

VSD jacking system benefits The safety issues this paper addresses are in context of motorized rack-and-pinion jacking systems using VSD technology that is controlled by programmable logic controllers (PLCs). These are examples of Integrated Drive Systems that enhance productivity, reduce the total cost of ownership and benefit from the simplicity of a single point of contact at every stage of the drive train’s life cycle.

VSD jacking systems have numerous advantages over DOL drives and hydraulic systems, with many of those advantages providing inherent measures of additional safety. Among them:

• Better pinion load control eliminates the need for a special high slip-motor, reducing wear on the rack and the pinion resulting in longer life and less maintenance.

• Torque-based holding power keeps the platform in place until all brakes are released or engaged. This avoids brake slippage that can cause sudden, extremely high pinion loads that will create undue metallurgical stress on the pinions. The VSD drive also allows for full torque at zero speed, opening the brakes to start from zero speed to maximum speed.

• Brake wear is reduced because PLCs provide precise control of the jacking motor torque via the PLC-controlled VSDs and jacking speeds are reduced to zero before brakes are applied.

• System stresses are reduced because the system’s integration into the jacking structure spreads load-bearing burdens among components that are specifically engineered to bear those loads and minimizes stresses, especially sudden excessive ones.

• Smooth, quiet operation reduces on-board personnel stress, while energy-efficiency reduces fuel requirements, saving space, weight and costs.

• Jacking time will be quicker and safer using an Integrated Drive System. Accurate measurement of rack and pinion location will provide safe and standardized raising and lowering of the vessel’s legs.

More specifically, this paper will analyze the operations of a jackup rig platform that is triangular and supported by three triangular legs. Raising and lowering of each leg is done by a group of VSDs and induction motors connected to helical-planetary gear reducers. The reducers have large gear pinions on the output that mesh with the rack on the chords of the legs. PLCs control the VSDs and their motors, which are equipped with mechanical, spring-loaded brakes to prevent movement when power is off. Motors are also fitted with incremental encoders for closed-loop speed. Almost all rigs feature manually operated rack chocks in their jacking system that fixes the rack with the hull, thereby releasing the drive train from the hull load.

32 White Paper | Offshore jackup rigs | September 2013

A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved. A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved.

White Paper | Offshore jackup rigs | September 2013

Keeping the platform level during jacking operations can be done manually or automatically via the PLC, with a technician overseeing the automated PLC process by means of the jacking system’s human-machine interface (HMI).

Principles of automatic leveling A platform’s horizontal level is measured electronically with a bubble-type inclinometer (also called a tilt meter). The inclinometer must be of sufficient resolution that it can measure inclination extremes at least twice the maximum allowable inclination of the platform, usually five-degrees. In addition, the device’s response time should be faster than the maximum acceleration and deceleration times of the rig’s jacking system, accounting for drive train inertia and hull momentum, so the jacking control system can react with minimum delay.

There are two types of automatic leveling control systems: dual-axis and tri-axis. In a dual-axis system, the inclinometer is mounted so that one axis measures the platform tilt in one direction and the other axis measures the platform tilt in the other direction, 90-degrees apart. In a tri-axis system, three inclinometers are used, each mounted in a straight line between the center points of each rig leg, forming a triangle. Alternatively, tri-axis leveling can be achieved mathematically using a dual-axis system.2

While various manufacturers provide dual-axis control systems that are currently deployed on offshore jackup rigs in the Middle East, Southeast Asia and the Gulf of Mexico, Siemens makes and sells automated VSD jacking systems with PLCs and recommends using tri-axis leveling controls for two reasons. One is that deviations in the polar rotation of dual-axis systems produce an undesirable platform “wobble” that must then be controlled, in contrast to tri-axis control systems that do not produce such an effect. The other is that, overall, tri-axis systems achieved level platform conditions 30 percent faster and with 30 percent less distance than dual-axis control systems.

Offshore jackup rigs – workhorses of the oil and gas industry Safety first – keeping a jackup rig’s platform level

Figure 1. Dual-axis inclination orientation Figure 2. Tri-axis inclination orientation

Page 3: Jackup Rig Whitepape FINAL LoRes Spreads

54 White Paper | Offshore jackup rigs | September 2013 White Paper | Offshore jackup rigs | September 2013

Putting countervailing forces to work Here’s how an automatic leveling system works: The speed of a jack rig’s legs when raised or lowered is controlled by PLC, which dictates the required speeds of the VSDs and their motors. The PLC keeps the platform level by reading the inclinometer’s values and then independently increasing or decreasing the drive speed of each leg as needed to maintain a zero-degree inclination on the system’s two or three axes.

To illustrate, consider a rig’s platform that’s being raised after its legs are safely seated on the sea floor. If the inclinometer indicates the platform’s bow is too high, the PLC will command

the bow drives to decrease jacking speed on the bow leg while simultaneously commanding the jacking drives on the port and starboard legs to increase their speeds.

As these respective motions level the platform, the inclinometer’s values will move toward zero. In response, the PLC will begin to reduce its speed commands to the drives in each leg. This process continues until the output of the inclinometer reaches zero, indicating that the platform is level. At that point, the PLC will once again command the drives to operate at the same base jacking speed.

Safety first – keeping a jackup rig’s platform level (continued) Safety first – no single points of failure

While keeping a jackup rig’s platform level is the primary function of its jacking system after its legs are securely set on the sea floor and the hull platform is raised to the specified height, the jack system itself must be designed without any single point of failure. Like any complex system operating in an unforgiving environment with human lives or a critical mission at stake (e.g., manned spaceflight or the Hubble telescope), system redundancies provided by a layered architecture help to minimize the risk of catastrophic failure.

This critical design principle should apply to the jacking systems of all offshore jackup rigs, but unfortunately many manufacturers of jacking systems have not followed this guideline, nor have owners required them to do so, for obvious reasons of cost. However, a catastrophic rig failure in Singapore in late 2012 has prompted the American Bureau of Shipping (ABS) and other maritime standards-setting bodies to discuss much stricter standards for jackup rigs such as requiring greater system redundancies in their jacking systems.

The inherent safety with jacking system control system using a layered architecture is this: if a problem occurs in the operational layer comprising a drive, motor and gearbox jacking assembly, that layer can be shutdown and the hull or legs can still be moved by means of the remaining layers, although at a lower speed and with each redundant assembly layer assuming more of the overall load. However, with a single leg jacking control system, the entire jackup rig becomes completely inoperable (i.e., “dead in the water”) until help arrives, if one leg loses its jacking capability.

Below lists the redundant components that Siemens recommends for the jacking systems it designs and builds for its customers:

• Two PLCs in protective cabinets, each operating synchronously and redundant to the other and providing real time monitoring of all phases of jacking operations including platform leveling and RPD adjustments;

• Each pinion controlled by a system comprising a gearbox, motor, brake, encoder and VSD, to provide precise and redundant torque and position control (e.g., RPD) for each leg’s rack and pinion jacking system;

• Two tri-axis inclinometer leveling systems, each operating synchronously and redundant to the other;

• Two Windows-based color HMI control screens with keyboard, mouse and joystick controls, each operating synchronously within the central control room and redundant to the other;

• Three remote input/output (RIO) cabinets, one for each rig leg;• Three local leg operator stations, each with three “flying lead”

boxes, which are local panels connected via cable to the RIO cabinets;

• Two self-healing optical ring networks, each using PROFINET industrial Ethernet with highly deterministic, isochronous real-time (IRT) data exchange cycles of under 10 milliseconds, which are required for motion control applications like jacking operations.

In addition, the safety of this layered architecture for jacking systems needs augmentation with standard industrial safety devices including emergency stops (i.e., E-stops) that, when pressed, activate the jacking system’s spring-loaded brakes for an emergency shut-down-in-place. These are wired to the PLC for monitoring and identifying any activated E-stop.

Rack chock systems

If a jackup rig employs a rack chock system, each

leg has one. These typically use seven-toothed

steel chocks that engage the opposed teeth of a

leg’s rack. When engaged, these relieve the pinions

and brakes of their holding stresses, which helps

reduce maintenance and prolong their lifecycles.

Although engaging and disengaging rack chocks

is usually done manually via remote, hydraulically

powered mechanical screw jacks, a PLC-controlled

VSD automated jacking system can be used to gently

lift the rigs massive weight off the chocks before

disengaging the rack chocks.

A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved. A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved.

Page 4: Jackup Rig Whitepape FINAL LoRes Spreads

76 White Paper | Offshore jackup rigs | September 2013 White Paper | Offshore jackup rigs | September 2013

Siemens is a single source solutions supplier for the entire oil and gas industry value chain, including upstream, midstream, and downstream segments worldwide. For both onshore and offshore oil and gas projects, it provides reliable, innovative, efficient and environmentally friendly products, systems, and solutions designed to operate under the industry’s most demanding conditions. In particular, Siemens Drive Technologies offers Integrated Drive Systems, which are drive-train solutions comprised of components drawn from its comprehensive portfolio of electrical motors, variable frequency drives, gear units, and couplings tailored to the rugged

Safety always – a guiding principle for jackup rig design

Although designing offshore jackup rigs to operate with zero risk is impossible to achieve, Siemens believes that such an ideal is worth striving for. No less than our founder, Werner von Siemens, laid down this guiding principle in 1880 when he said, “The prevention of accidents must not be understood as a regulation required by law, but as a precept of human responsibility and economic reason.”

Given the advanced age of the world’s fleet of offshore jackup rigs, a new generation of rig designs will soon be emerging from the CAD-based drawing boards of naval architects and maritime engineers across the industry. The advancements in PLC-based automation controls and VSD technologies offer them a tremendous opportunity to design jackup rigs in ways that mitigate risk and optimize operational capability.

About Siemens Integrated Drive Systems for the Oil & Gas Industry

requirements of the oil and gas industry. Integrated Drive Systems have been proven to improve system reliability and productivity, while reducing project risk. Siemens backs its extensive system knowledge in marine applications by a global support structure, including preventive maintenance, remote condition monitoring and onsite service to help rig operators minimize the risk of expensive downtime.

For more information, please visit: usa.siemens.com/ids or usa.siemens.com/oil-gas.

Siemens Integrated Drive Systems enhance rig operators’ productivity, reduce the total cost of ownership and offer the simplicity of a single point of contact, at every stage of a drive train’s life cycle. In addition, the three-fold integration approach depicted above offers comprehensive software tools and expert services from planning, engineering, and execution all the way through to services. This provides maximum investment protection.

A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved. A white paper issued by Siemens. ©2013 Siemens Industry, Inc. All rights reserved.

References1 ODS-Petrodata, RS Platou Markets2 Edward (Ted) Fowler, Three-Leg Jackup Platform Automatic Inclination-Leveling Control Systems

(Houston: Siemens Energy, Oil & Gas Division, 2009), p. 11.

Page 5: Jackup Rig Whitepape FINAL LoRes Spreads

usa.siemens.com/ids

Subject to change without prior notice Order No.: DTWP-00004-0913 Printed in USA © 2013 Siemens Industry, Inc.

Siemens Industry, Inc. 3333 Old Milton Parkway Alpharetta, GA 30005 1-800-241-4453

[email protected]

The information provided in this white paper contains merely general descriptions or characteristics of performance which in case of actual use do not always apply as described or which may change as a result of further development of the products. An obligation to provide the respective characteristics shall only exist if expressly agreed in the terms of contract.

All product designations may be trademarks or product names of Siemens AG or supplier companies whose use by third parties for their own purposes could violate the rights of the owners.