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SPECIAL REPORT

Next Generation Load Instrumentation, Measurement and Monitoring Solutions

Offshore Monitoring Solutions Other Forces at Work Extended Life Needs Greater Vigilance Offshore Assets and What Stress Can Do Sponsored by

Load, Stress and Strain; Measurement and Monitoring

Published by Global Business Media


Through life monitoringProtecting your assets Hull StressAlert system installed in FPSO Terra Nova

Bespoke Monitoring Solutions backed by 50 years industry experience. Continuous innovation and development by Strainstall provide the monitoring solution to meet your unique requirements in extreme environments. Monitoring covers but not limited to: Hawser Tension

Mooring

IMMS

Hull Stress

Load Equipment Turret Mooring

Riser Tension

Position

MetOcean Tendon Tension

Ballast Tank

www.strainstall.com

Structural


SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

SPECIAL REPORT

Next Generation Load Instrumentation, Measurement and Monitoring Solutions

Contents Foreword 2 John Hancock, Editor

Offshore Monitoring Solutions

3

Next Generation Load Instrumentation, Measurement and Monitoring Offshore Monitoring Solutions Other Forces at Work

Dr Phil Cutter, Strainstall UK Ltd

Extended Life Needs Greater Vigilance Offshore Assets and What Stress Can Do Load, Stress and Strain; Measurement and Monitoring

Sponsored by

Published by Global Business Media

Published by Global Business Media Global Business Media Limited 62 The Street Ashtead Surrey KT21 1AT United Kingdom Switchboard: +44 (0)1737 850 939 Fax: +44 (0)1737 851 952 Email: info@globalbusinessmedia.org Website: www.globalbusinessmedia.org Publisher Kevin Bell Editor John Hancock Business Development Director Marie-Anne Brooks Senior Project Manager Steve Banks Advertising Executives Michael McCarthy Abigail Coombes Production Manager Paul Davies For further information visit: www.globalbusinessmedia.org

Company Profile 1. Introduction 2. FPSO Mooring Monitoring Case Study 3. Subsea Monitoring Case Study 4. System Integration

Other Forces at Work

8

John Hancock, Editor

Prospects for Long Term Growth Venturing Into Ever Deeper Waters A Future of Growing Challenges Different Ways for Increasing Production

Extended Life Needs Greater Vigilance

10

Peter Dunwell, Correspondent

Extending Productive Life and Reach The Need for Reliable Information Not Only Oil and Gas

Offshore Assets and What Stress Can Do

12

Francis Slade, Staff Writer

Offshore Structures and Equipment Load, Stresses and Strains Where Stresses Matter

The opinions and views expressed in the editorial content in this publication are those of the authors alone and do not necessarily represent the views of any organisation with which they may be associated.

Load, Stress and Strain; Measurement and Monitoring

Material in advertisements and promotional features may be considered to represent the views of the advertisers and promoters. The views and opinions expressed in this publication do not necessarily express the views of the Publishers or the Editor. While every care has been taken in the preparation of this publication, neither the Publishers nor the Editor are responsible for such opinions and views or for any inaccuracies in the articles.

Understanding Load Induced Stress and Strain – Hooke’s Law Why Stress and Strain Measurements Matter Monitoring Load and Stress is a Requirement What is used to Measure and Monitor Loads?

14

John Hancock, Editor

References 16

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Foreword W

HEN THINGS break in an offshore

The article looks at emerging trends in offshore load

environment, the results are of ten

monitoring, offshore monitoring in general and the new

catastrophic resulting in loss of production,

solutions that are now available to significantly improve

pollution and, worst of all, loss of life. However,

safety offshore.

breakage is rarely a completely isolated incident or

The second piece takes the broadest view of what

without prior changes in the condition of whatever

drives demand plus what other economic and market

has broken. Usually, a break is preceded by an

forces affect the offshore sector. We also examine the

increase in loads on a structure and/or a reduced

issue of safety throughout the life cycle of offshore

ability to cope with loads. Either way, this can usually

resources and the facilities used to extract them.

be identified in advance of any catastrophic event

Peter Dunwell then looks at the demands placed on

with proper monitoring of the loads and stresses

offshore structures and the loads that affect them.

on structures and their materials. There also needs

He also considers the other forces at work and, in

to be a system to convey that information to the

particular, the impact of operation installations beyond

operator as a basis for further action. In this Special

their original design life.

Report we look at a key contributor of information in

Francis Slade then looks at the effects of the

this respect – load instrumentation, measurement

challenging environment in which offshore installations

and monitoring solutions and the context in which

have to operate and how this translates to additional

they are used.

loads and stresses on the structures and equipment

The Report opens with an article that looks at

that make up those installations. Finally we consider

Strainstall UK Limited, a broad-based engineering

what load and stress are, the possible effects of

business that specialises in load measurement and

changes and how operators cam measure and

sensor based safety technology. The introduction

monitor any changes to avoid the kind of catastrophic

of Human Machine Interfaces (HMI), low cost data

breakages referred to above.

storage and new sensing technologies have provided a large range of options to give robust and accurate solutions to most load monitoring requirements. In offshore activities, this is of importance in monitoring mooring tensions, and is particularly relevant with the new ultra-deep water floating production platforms.

John Hancock Editor

John Hancock joined as Editor of Offshore Reports in early 2012. A journalist for 25 years, John has written and edited articles and papers on a range of engineering, support services and technology topics as well as for key events in the sector. Subjects have included aeroengineering, auto-engineering and electronics, high value manufacturing, testing, aviation IT, materials engineering, weapons research, supply chain, logistics and naval engineering.

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Offshore Monitoring Solutions Next Generation Load Instrumentation, Measurement and Monitoring

Discover innovative solutions to offshore monitoring systems

Dr Phil Cutter, Strainstall UK Ltd

Company Profile Strainstall is a member of the James Fisher and Sons plc group. The company is a broad-based engineering business, specialising in load measurement and sensor based safety technology. Based in Cowes, Isle of Wight, it has long been associated with the manufacture of standard and bespoke load cells, and has 50 years of experience in assisting industries to operate safely by ensuring that structures, equipment and infrastructure are safe to use. Through continuous innovation and development, Strainstall has a range of world-class monitoring technologies that continuously monitor physical and performance parameters such as load, stress, temperature, acceleration, pressure and displacement. To date, Strainstall has designed, manufactured and commissioned systems that measure force and strain in over 1,000 structures and applications including the world’s largest ship, the world’s tallest building, the world’s deepest FPSO and the world’s largest floating crane, as well as structural health monitoring installations on offshore wind turbine structures.

1. Introduction The use of monitoring systems offshore is well-established. Progressive improvements in technology have resulted in our ability to add monitoring systems to offshore hardware in more locations, in harsher environments and with more reliability. In terms of the instrumentation supporting the sensors within these systems, as an industry we are fortunate to have access to a variety of established and reliable means of interconnection and integration with which to design and build. The traditional approach to most load monitoring requirements was to place a load cell in-line with the load to provide a direct measurement with a local display. With the introduction of Human Machine Interfaces (HMI), low cost data storage and new sensing technologies there

are a multitude of options to provide robust and accurate solutions.

From concept to completion

1.1. Offshore Load Monitoring Load sensing offshore is predominantly concerned with monitoring mooring tensions. These obviously have a large impact on the overall safety of the vessel or platform in question. Typical platform types include Tension Leg Platforms (TLP), FPSOs, Semi-Submersibles, CALM buoys, Jack-Up Rigs and SPARs. The variable nature of met-ocean conditions dictate that monitoring of mooring loads is critical in many regions of the world. This is particularly relevant with the new trend of ultra-deep water floating production platforms. On many vessels and platforms, the mooring loads alone do not give the operators adequate information to assess the overall safety. More and more the trend is to integrate multiple monitored parameters into a single interface. These parameters will typically include metocean conditions, riser tensions, vessel position and motions, hull bending stresses and ballast levels. On any given vessel there will be multiple monitoring systems and standard communication protocols which now means the transmission of data from one system to another can be done between different suppliers with relative ease. Alarms can be sent from a mooring monitoring system to a centralised Integrated Control and Safety System (ICSS). This article will take a look at emerging trends in offshore load monitoring, offshore monitoring in general, and the new solutions that are now available to significantly improve safety offshore.

Stress Alert system installed in Artic Discoverer

With 50 years of experience, we can provide a complete ‘one stop’ package to the offshore industry.

2. FPSO Mooring Monitoring Case Study As previously explained, monitoring the mooring loads on a floating platform will vary depending on the platform type. There are several parameters to consider when specifying an appropriate

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

The variable nature of met-ocean conditions dictate that monitoring of mooring loads is critical in many regions of the world. This is particularly relevant with the new trend of ultra-deep water floating production platforms

CHAIN STOPPER INCLINOMETER TO MEASURE CHAIN STOPPER ANGLE

monitoring technology and the following will need to be considered: Accuracy Reliability Redundancy Maintenance Cost If we consider a turret-moored FPSO, there are several ways in which mooring tensions can be measured and each has its benefits.

angle measurement approach does not achieve accuracy as high as a direct load measurement, but it is usually sufficient, and importantly, can give a better indication of anchor leg failure, should a breakage occur near the seabed. With direct load measurement, a chain failure near the seabed may not trigger any alarms if the weight of chain still imparts a significant force on the chain stopper. There have been several instances of this occurring worldwide, and the failures have only been picked up during annual ROV surveys.

2.1. Angle Measurement

2.2. Direct Load Measurement

For catenary moorings the tensions can be calculated using the catenary equation. This requires the monitoring of three parameters, namely the chain angle, turret offset and distance to the seabed. The chain angle is measured using an inclinometer fixed to the chain stopper, the turret offset is measured with a GPS and the depth is typically calculated with draft and tidal data. With this approach, minimal re-design of existing mooring hardware is required, as the sensors are bolted to the chain stopper so repair or replacement can be easily affected. The

Direct load measurement typically provides the most accurate load monitoring solution. There are two general approaches on FPSO turrets and each has its own merits. A load measuring pin is often able to replace an existing pin in a loading assembly so requires minimal re-design to the whole mooring arrangement. This typically gives a direct load output and redundancy can be built in with each load pin having two separate sets of strain gauges and two identical outputs. The other option that can be applicable where stopper plates are used to hold the chain links is to measure the compressive force applied

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Strainstall is at the forefront of innovative solutions to ship and platform structural monitoring systems

WELDED SEALED LOAD PINS SUITABLE FOR HAZARDOUS AREA USE

Protect your assets by the stopper plate to the chain stopper tube. This again is a direct form of measurement and generally has a high level of accuracy. Typically, three or four compressive load cells are fitted into recesses machined into the chain stopper and the stopper plate rests on these. The advantage of this approach is that it enables easy removal of load cells for repair or replacement, although it does require an element of re-design to accommodate the load cells.

2.3. Strain Measurement An approach that is becoming more and more popular in terms of mooring load measurement is to use a bolt-on sensor to monitor the strain on a chain stopper, which is directly proportional to the load. Strainstall’s unique Strain Rings were developed specifically with this application in mind and these sensors have been deployed in numerous offshore mooring applications around the world. They are most commonly used in dualarticulating chain stoppers that are designed to minimise out-of-plane chain link bending. These chain stoppers, used on both turret-

moored and spread-moored FPSOs, typically have a stopper plate at the end of the chain stopper tube, thus subjecting the tube to a relatively uniform tensile load. The Strainstall Strain Rings are bolted onto welded fixings on the chain stopper and measure the induced strain in the tubes. The sensors are completely sealed in a 316 stainless steel housing and suitable for use in zone 0 areas as well as subsea. They offer a number of advantages over other monitoring techniques; they are not load bearing and so do not require the stringent materials, manufacturing controls or costs associated with such components. Their bolt-on fixings means that they can be interchanged for repair or replacement as necessary. In addition, their high resolution and dynamic response provides a high accuracy measurement solution.

3. Subsea Monitoring Case Study Subsea monitoring of loads, vibrations, current profiles and positions is not a new concept. Most of Strainstall’s sensors, including load cells, inclinometers, accelerometers and strain rings are manufactured with subsea housings. However, their use can be limited by the transmission

Hull Stress Monitoring Systems Provides access to the vessel’s real-time structural integrity as a result of wave or cargo induced static and dynamic loading.

www.strainstall.com SUBSEA RATED STRAIN RINGS DESIGNED FOR HARSH OFFSHORE ENVIRONMENTS

T: +44 (0)1983 203600 E: enquiries@strainstall.com

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Often cables are the weakest link in a subsea monitoring system, so their specification and installation are critical to achieving the long-life expected of them

of data back to the platform. Long subsea cable runs are susceptible to damage as often adequate support and protection is not practical. Therefore, the use of acoustic modems underwater is becoming more prevalent and provides a solution to data transmission over large distances. The range and dexterity of Remotely Operated Vehicles (ROV) also enables maintenance and battery changes to be made for such systems. Strainstall’s Integrated Marine Monitoring System (IMMS) for Total’s Moho Nord project utilises such technology in order to monitor the position of subsea buoyancy modules. In this instance a single unit monitors and reports the pressure data to a platformmounted receiver up to 800 metres away. An ROV-replaceable battery provides a 5 year life expectancy, and multiple buoyancy modules in the field are monitored simultaneously, with data fed to the platform’s IMMS. Alarms allow action to be taken in the event of a failure or change in status.

3.1. Subsea Connectors and Cable Another area of development for subsea monitoring system reliability is the robustness of connectors and cables. Strainstall have worked with sister company RMSpumptools to develop a new type of connector for deployment on the latest generation TLP tendon tension monitoring systems. The load cells in these systems are located around 50m subsea and once installed cannot be replaced during the 30+ year lifetime of the platform. The use of connectors allows cables to be changed out as required if excessive wear occurs.

SEACONNECT TM CONNECTORS SUITABLE FOR DIVER OR ROV SUBSEA MATING

T h e R M S p u m p t o o l s S e a C o n n e c t TM electrical connectors provide a wet mate connection for all subsea monitoring requirements. In common with other high-end connectors, this design provides a double seal between the environment and the critical electrical signals contained within. Copper and cupronickel alloys are used for functioncritical components, and coupled with the use of inert low-friction polymer coatings, this is the only connector designed specifically to deal with marine-growth. High-grade stainless steels are used for anti-corrosive and mechanical properties in structural and pressurised casing components. Often cables are the weakest link in a subsea monitoring system, so their specification and installation are critical to achieving the long-life expected of them. For the most function-critical applications, Strainstall has cable designed and manufactured specifically for the application. In addition, the way in which cable installations are designed is vitally important; time spent at this stage will pay dividends on the project long-term.

4. System Integration As previously discussed, monitoring mooring loads in isolation does not necessarily provide the platform operators with all the information

TYPICAL IMMS SOFTWARE HOME SCREEN FROM RECENT TLP PROJECT

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

they require to take action to ensure continued safe operation. Strainstall’s recent project for the Moho Nord TLP illustrates how multiple parameters can be effectively monitored and displayed in a manner that allows operators to quickly assess platform safety. For this particular system the following parameters are being monitoring as part of a single Integrated Marine Monitoring System (IMMS): Tendon Tensions Environmental Riser Tension Winch Monitoring Position and Motion Ballast The screenshot on the previous page shows how these parameters are displayed and the graphical representation of each parameter allows the user to quickly assess the status of a given aspect of the platform. For more detailed assessment of the particular monitored parameters the user can click through on each graphic to see and download the numerical data. The system also interacts with the loading computer in order to feed relevant live-stability data into the software. The software can be user-configured to send alarms to other platform software systems such as ICSS and also feeds relevant data into a cloud-storage system to enable remote access to live and archived data.

4.1. Wireless Future Throughout the history of offshore monitoring, the display of data from each sensor has moved from being locally displayed to centrally displayed data and with modern networking capabilities data can be displayed in multiple locations on a platform. Strainstall have moved this technology on one step further to enable users to monitor individual sensors using wireless technologies. Strainstall have developed a range of lowpower zone 1 and 2 wireless transmitters that can be used in conjunction with multiple sensors such as load cells, flow meters etc. Each transmitter has its own unique tag and also internal data storage. A typical transmitter range is over 200 m and with a Strainstall handset any sensor in range can be connected to show the live status. All handsets are

Enhance safety with Strainstall’s bespoke solutions to load measurement equipment and monitoring systems

High performance

WIRELESS HAZARDOUS AREA HANDSET TO VIEW STATUS OF MULTIPLE SENSORS

interchangeable and certified for hazardous areas. This will enable an operator to move from place to place on a platform and connect with any given sensor in range. Alternatively, as required, the technology can be provided with smartphone or tablet connectivity. This will enable Apple or Android devices to display live sensor statuses. With the use of appropriate smartphone cases these devices can also be used in hazardous areas. IMMS installed on TLP Shenzi

Contact

Integrated Marine Management System Strainstall UK Ltd 9-10 Mariners Way, Cowes, Isle of Wight, UK Tel: + 44 (0) 1983 203600 Fax: + 44 (0) 1983 203645 Email: info@strainstall.com Web: strainstall.com

Comprehensive monitoring and control systems that comprise of multiple sub-systems including mooring, ballast, riser, met-ocean, position and motion monitoring. Strainstall manufacture and supply instrumentation, signal conditioning and software for a complete system.

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Other Forces at Work John Hancock, Editor

It isn’t only engineering needs that determine the demand for any equipment and systems in offshore oil and gas

In addition to any growth prospects, safety requirements are non-negotiable for installations and equipment currently in use in the sector. It adds up to a significant challenge. Like safety, monitoring will not be an option – it will be a necessity

Measurement and monitoring of loads, stresses and strain is a key element in the high tech and demanding process of finding and producing oil and gas from under the sea. It is also, as are other elements in that process, subject to the broader influences that the global economy in general, and the energy economy in particular, brings to bear on the sector. At the time of writing (the end of 2014) neither of those were exhibiting the kind of certainty that would encourage new investments but that might not be so important for measurement and monitoring or in the longer term.

Ninety five per cent of that growth in demand is expected to come from the emerging economies, while energy use in the advanced economies of North America, Europe and Asia as a group is expected to grow only very slowly – and begin to decline in the later years of the forecast period [to 2035].” In the same paper, BP Chief Economist Christof Rühl says: “This process shows the power of economic forces and competition. Put simply, people are finding ways to use energy more efficiently because it saves them money.”

Prospects for Long Term Growth

Venturing Into Ever Deeper Waters

Views vary but, taking the long view, the world’s population continues to grow and, with little prospect that sustainable or renewable resources will be sufficiently developed to fill appetites for energy in the near future, there is every chance that demand for resources will resume its growth trajectory in the future. That reality underpins the incentive to find further reserves of carbon based fuels. But any as yet unexploited reserves tend to be in inaccessible or hostile environments… or both. Few environments could be more inaccessible or hostile than the oceans but significant reserves of oil and gas are to be found at ever increasing distances from land, far beneath sea-beds that are themselves under the deepest of waters. These environmental realities alone will impose greater loads, stresses and strains on installations and equipment than even those that have been faced to date. Also, in addition to any growth prospects, safety requirements are nonnegotiable for installations and equipment currently in use in the sector. It adds up to a significant challenge. Like safety, monitoring will not be an option – it will be a necessity. All that said, demand growth will not be equal across the sector so that while, as BP Energy Outlook 20351 puts it, “… global energy consumption is expected to rise by [only] 41 per cent from 2012 to 2035 – compared to 55 per cent over the last 23 years (52 per cent over the last twenty) and 30% over the last ten...

In 2013, in the ‘Market’ paper ‘Deepwater and Beyond’, Petrofac2, quoting Business Insider Website, explained; “The deepwater sector is one of the fastest growing markets in the upstream oil and gas industry. This is largely due to steady technological improvements, increasing energy demand and depleting shallow water resources. Since 2000, new offshore discoveries have amounted to more than 200 billion barrels of oil (approximately 18 billion barrels equivalent a year).” The significance of this for any technology associated with the demands of offshore production is further reinforced with the comment that, “There are 181 offshore fields internationally which have an average water depth of 1,896 ft. However, offshore activity is most concentrated in deeper water.” Axiomatically, the deeper the water is over a field, the greater the loads, stresses and strains on installations and equipment and the higher the need to be able to accurately measure and monitor them. Increasingly challenging environments, complex engineering, life extension and ever tightening regulations have to be considered in any assessment of the market. But as well as these qualitative requirements, there is also a more traditional quantitative growth as the amount of equipment and infrastructure also grows. Following a period in which the 2009 financial crisis and the Gulf of Mexico oil spill limited growth in subsea hardware spend, “Douglas-Westwood3

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Strainstall is at the forefront of innovative solutions to ship and platform structural monitoring

TENSION LOAD CELLS FOR AIRCRAFT ASSEMBLY

forecasts global subsea hardware Capex will total $117 billion (bn) between 2014 and 2018. This represents growth of more than 80% compared with the preceding five-year period.

A Future of Growing Challenges This next phase of global offshore oil and gas development will not be without its challenges. Sarah Blackman in the June 2012 issue of Offshore Technology4 explained; “The days of cheap and easy-to-drill oil are over. Now comes the hard work of finding and producing oil from more challenging environments… [to this end] oil and gas firms are looking to squeeze every last drop of reserves from the nooks and crannies of the ocean, in hard-to-reach, ultradeep places.” As well as venturing into difficult locations, engineering is also being challenged, not only to make production possible in difficult places but also in the quest to extend the life, reach and capability of installations already in production. So, it isn’t only the growth of new fields but also the life extension of established fields that is stretching oil and gas production life cycles to extents that were not previously planned and that, in turn, require equipment to be used some way beyond its anticipated working life.

Different Ways for Increasing Production As The Journal of Petroleum Technology5 put it, “More than half of the offshore oil and gas installations in the UK Sector of the North Sea have been operating for at least 20 years. Most assets are approaching or operating beyond their

original design intent. With the rise in oil and gas prices [at the time that article was written] and advances in technology, there is an increasing requirement to extend the operational life of these assets. Safety-case regulations were modified to include a technical justification for extended operation, and the UK Health & Safety Executive (HSE) launched Key Programme 4 (KP4) to ensure that all duty holders have suitable management systems in place to address aging-related issues adequately.” Equipment in these life-extended fields will require increasingly stringent and detailed levels of inspection and testing to ensure their continuing operating efficiency and structural integrity and that will include robust and reliable measuring and monitoring capabilities. As well as new field developments and the extended life for older fields, there is a third way in which growth can be achieved. As Offshore Technology explained in the March 2007 article, ‘Tieback Time’6, “Subsea tiebacks connecting new discoveries to existing facilities can extend the life of production infrastructure. They are becoming increasingly viable, both technically and economically… Exploiting new discoveries using existing production facilities is an important way of obtaining maximum value from existing infrastructure.” But it also raises the bar on measuring and monitoring the loads, stresses and strains imposed on installations and equipment. There is no doubt that, at the time of writing, the global offshore oil and gas sector faces some uncertainty but that is not likely to result in any reduction in vigilance and understanding required from operators.

Mooring monitoring on FPSO PSVM

Strain Rings A unique Strainstall designed and manufactured instrument that enables high accuracy load monitoring in subsea or hazardous areas. The bolt-on design facilitates simple integration with existing assemblies.

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Extended Life Needs Greater Vigilance Peter Dunwell, Correspondent And greater vigilance needs better understanding of installations and equipment and the forces that affect them

An increasing number of fields, especially in the more mature reserves, are having their life and/or reach extended, leveraging the latest engineering to extract every last drop of recoverable product from a reserve

A

CCORDING TO Robert Lamb’s article, ‘How Offshore Drilling Works’7 for ‘How Stuff Works’, “Most of the world’s petroleum is trapped between 500 and 25,000 feet (152 and 7,620 meters) under dirt and rock.” That is the underlying challenge increasingly facing oil and gas producers and largely accounts for most of the high tech and very costly equipment, not to say the sophisticated processes and software solutions that are associated with any oil and gas extraction programme. However, what it all boils down to is that to access oil and gas reserves you have to locate a platform or other vessel over a hole in the seabed where the structure itself and its associated equipment will be subject to a range of loads, stresses and strains.

Extending Productive Life and Reach To compound those engineering challenges, not all oil deposits are conveniently located under land or below shallow waters (see previous article) which means that, while many of the more easily accessible fields are already well into their productive life, new reserves are increasingly located beneath deep oceans and even beneath the Arctic ice. It all adds up to a scenario in which the more information about the condition of equipment that can be mustered and the sooner it can be accessed, the better. Starting where the previous article ended, an increasing number of fields, especially in the more mature reserves, are having their life and/or reach extended, leveraging the latest engineering to extract every last drop of recoverable product from a reserve. Demand and economics are the two principal drivers of life extension programmes. Demand is obvious: with growing numbers of economies moving from ‘third world’ to ‘emerging’ status (and, ultimately, on to ‘developed’), the need to fuel all of those economic expansion programmes

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means that ever more oil and gas reserves have to be found and produced. In part, that drives the economic case for field life extension because, up until recently, when increased demand met finite resources, prices rose. However, whether because prices have risen or have fallen, as is the case at the time of writing, with the cost of capital items being so great, purchasing new equipment and structures can significantly offset any economic benefit in times of high prices and compound the cost side of production when prices are low: plus the opportunity to wrest increased productive life from older equipment will be welcome. Extension is just an elongation of the production phase in a field’s life. The life stages through which installation pass mirror the life stages of a field… exploration, proving reserves, building and installing structures, production and maintenance, decommissioning, and dismantling or making safe. During every one of these life stages and, although it is often a challenge, effective and detailed data is required for valuable asset integrity assessment and possible lifetime analysis.

The Need for Reliable Information The Journal of Petroleum Technology, February 2012 edition8, although written in times of high prices, summed up the situation. “To keep capital and operational expenditures at a minimum, there is an increasing requirement from operators to use existing infrastructure, and, consequently, there is a trend to use subsea tiebacks to existing platforms. Therefore, platforms become ‘hubs’ and often their operational life is extended. The result is that decommissioning is delayed and equipment that had been maintained at near-minimum levels now requires significant overhaul or replacement to continue service for another 10 to 20 years… Extending the life of existing assets ultimately results in installations operating


SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Enhance safety with Strainstall’s bespoke solutions to load measurement equipment and monitoring systems

HOOKS IN PRODUCTION

LDD ON SHORT PEDESTAL

well beyond their original design life. However, the aging of facilities can have a direct effect on installation integrity and safety… Aging and life extension are major issues for the offshore oil and gas industry… Aging is not about how old the equipment is; it is about what is known about its condition, how that is changing over time, and how effectively the associated risks are being managed.” As always, information is all important and that means reliable measurement and monitoring systems.

Not Only Oil and Gas And it isn’t only measuring and monitoring information that poses a challenge: once gathered, information needs to be transferred to a system where it can be analysed and, if necessary, inform any action that might

be required. This is true for installations and equipment and for the anchor lines used to keep them in place. It’s also true for those other major energy installations that are growing in numbers in the offshore environment… wind turbines. In this context, the paper, ‘Results from monitoring and assessment of offshore wind turbines’9 explains that, “Monitoring systems for structural components have two basic tasks. After the completion and before commissioning the turbine in principle an experimental verification of design assumptions and the structural condition after the construction of the turbine offshore should be performed. On the basis of this information in the ‘zero state’ the ongoing operation will be observed in fields of load monitoring, stress monitoring and condition monitoring. The knowledge of the external loads acting on the rotor blades and the structure is of interest for the verification of design assumptions as well as information related to the optimization of the parameters for the operating system and for the damage identification.” The paper continues to explain that the task of the stress monitoring is to measure maximum and permanent strain continuously. Thus the required data for the current condition assessment of the structural elements against the limits of capacity and fatigue are made available. Measuring and monitoring tools are at the heart of safe operations for a whole variety of offshore engineering: without them engineers would be largely in the dark as to the strength and impact of forces acting on their structures and equipment.

TAD hawser monitoring on FPSO Oveng

Load Pins One of the simplest and most reliable methods of measuring loads. Strainstall’s load pins have been used in the some of the world’s most high profile structures including the world’s largest ship, floating crane and passenger airliner. When quality and performance are critical Strainstall has been the partner of choice for 50 years.

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

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SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Offshore Assets and What Stress Can Do Francis Slade, Staff Writer Looking at structures and equipment and how loads and stress can impact on them

Pipes are vulnerable structures which can be subject to considerable load related stresses if not properly supported and protected. Eventually, that can lead to loose joints or, even the worst nightmare for any offshore operator, crude oil leaking into the ocean

A

S WELL as understanding the economic context in which any technology works in the offshore sector, it is also useful to understand the engineering context. Subsea energy discovery and production engages many engineering achievements and activities that make up the specialist technology, equipment and operating methods used. As far as this Report goes, subsea refers mainly to offshore oil and gas facilities plus offshore renewable energy: demanding and costly activities undertaken in conditions most likely to add load and stress to every component in the process.

Offshore Structures and Equipment There are two types of offshore structure, fixed and floating. At the heart of operations are platforms. Oil and gas platforms10 are key fixed installations from which drilling and production activity is carried out. Drilling rigs are either floating vessels for deeper water or jack-up designs which are a barge with liftable legs. Both of these types of vessel are constructed in marine yards but are often involved during the construction phase to pre-drill some production wells. Other key factors in offshore construction are the weather window, which defines periods of relatively light weather during which continuous construction or other offshore activity can take place. These are more reasons why measurement and monitoring of loads and stresses are so essential. And platforms are not the only structures on or in the sea. Pipelines are as important, if largely invisible, components in any offshore energy complex, transporting product to where its value can be realised. But pipes are vulnerable structures which can be subject to considerable load related stresses if not properly supported and protected. Eventually, that can lead to loose joints or, even the worst nightmare for any offshore operator, crude oil leaking into the

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ocean. Even where a pipe is initially solidly founded, the effect of scouring can erode material from underneath the pipe, thus gradually creating new stresses where the pipe crosses unsafe spans.

Load, Stresses and Strains Given the tremendous demands of the environment in which the offshore oil and gas sector operates and the enclosed nature and isolation of most installations, everything has to be built to the highest structural, safety and operational integrity levels. But things can still go wrong and the cost in lost production and/or environmental damage can be enormous so condition monitoring is very important to alert to potential problems. They can result from a number of factors including the introduction of unplanned load or stress into a structure or equipment and the consequences can range from inefficiency to catastrophe. As the OGP Risk Assessment Directory11 explains, “Total Loss structural failure events are when an installation loses its ability to support its topside as a result of operational and environmental loading. Possible causes include: • Extreme weather; • Marine corrosion; • Fatigue; • Foundation failure; • Construction defects; • Design errors; • Earthquakes” As well as understanding loading, it’s also useful to understand what Stress and strain are in this context. Physics Net12 says, “The stress applied to a material is the force per unit area applied to the material. The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress. Tensile means the material is under tension. The forces acting on it are trying to stretch the material. Compression is when the forces acting


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on an object are trying to squash it.” A formula is then given to calculate stress before defining… “The ratio of extension to original length is called strain. It has no units as it is a ratio of two lengths measured in metres.” A further phenomenon that needs to be understood are the risks and hazards that can exert unplanned-for loads. Knowing what those risks and hazards are can enable operators to take sensible precautions and build in systems and procedures to enhance safety in normal circumstances. But none of that obviates the need to measure and monitor loads and stresses.

Where Stresses Matter One area where load monitoring is particularly critical is with anchors and hawsers. While many vessel anchoring systems can allow for quite a lot of vessel movement to disperse loads caused by weather and ocean movements, offshore drilling and production assets, linked to seabed wellheads, do not have the same degree of flexibility available for them. Anchoring needs in this respect require anything from stand-alone mooring load monitoring to comprehensive integrated systems which monitor all the factors at play, including vessel draft and ballast, metocean (meteorological and oceanic) conditions, vessel loading and structural

stress. The other structure where stress can have damaging consequences is in hulls. So it is important that the structural integrity of a hull, such as with an FPSO (floating production, storage and offloading) vessel, in which loads and/or stresses are at play is continuously monitored so that any changes in condition can be dealt with before they threaten the structure. According to LETS Global13, “One of the most common signs of early degradation in a vessel is the visual appearance of coating damage in weld connections subjected to high stresses.” The article continues to explain some of the weaker points in any vessel or structure and to emphasise the importance of monitoring as part of an inspection programme. The consequences of unplanned loads or of reduced structural ability to handle loads are spelt out in the UK HSE (Health & Safety Executive) paper ‘Technical policy relating to structural degradation and deterioration (including aspects of ageing)’14 “…actual failure will occur when the load bearing capacity of the remaining ligament is insufficient for the applied load... At this stage load shedding will take place and the applied loads will be transferred to neighbouring components.” Load measuring and monitoring makes it much easier to foresee such problems and take actions to deal with them before they increase further.

Stress Alert system installed in Artic Discoverer

With 50 years of experience, we can provide a complete ‘one stop’ package to the offshore industry.

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

WWW.OFFSHORETECHNOLOGYREPORTS.COM | 13


SPECIAL REPORT: NEXT GENERATION LOAD INSTRUMENTATION, MEASUREMENT AND MONITORING SOLUTIONS

Load, Stress and Strain; Measurement and Monitoring John Hancock, Editor Why do materials perform as they do under load and how can operators

Many metals follow Hooke’s Law until a certain level of stress has been applied, after which the material will distort more severely.

Understanding Load Induced Stress and Strain – Hooke’s Law The scientific principles upon which the application of load can adversely affect a material are encapsulated in Hooke’s Law which is described by University of Bolton AMI, in ‘The Mechanical Properties of Metals’15 as, “[Looking at a spring] if you gradually stretch it, the force needed increases, but the material springs back to its original shape when the force is released. Materials which react in the same way as a spring are said to be ‘elastic’. Typically if we measure the extension of different forces and plot the graph of this, we will find that the extension is proportional to the force applied. Materials that obey Hooke’s Law exhibit a linear relationship between the strain and the applied stress (Figure 1).

straight line behaviour

stress

The point at which

ceases is called the

stress s

limit of proportionality:

strain e

beyond this the material strain

will not spring back to

FIGURE 1: STRESS-STRAIN GRAPH FOR AN ELASTIC SOLID (SOURCE UNIVERSITY OF BOLTON AMI)

its original shape

Many metals follow Hooke’s Law until a certain level of stress has been applied, after which the material will distort more severely. The point at which straight line behaviour ceases is called the limit of proportionality: beyond this the material will not spring back to its original shape, and is said to exhibit some plastic behaviour (Figure 2).

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stress

measure and monitor that?

yield point

sample breaks

tensile strength

limit of proportionality

strain FIGURE 2: STRESS-STRAIN GRAPH FOR A TYPICAL METAL (SOURCE UNIVERSITY OF BOLTON AMI)

The stress at which the material starts to exhibit permanent deformation is called the elastic limit or yield point. As Figure 2 shows, if the stress is increased beyond the yield point, the sample will eventually break. The term (ultimate) tensile strength is used for the maximum value of tensile stress that a material can withstand without breaking, and is calculated at the maximum tensile force divided by the original cross-sectional area.” The paper continues to explain how, subjected to some types of force, a material will shear.

Why Stress and Strain Measurements Matter What engineers need to know, if load measurements are to be of any use, is what is called ‘breaking stress’ or ‘ultimate tensile stress’. The behaviour of materials under stress is a whole branch of engineering so we won’t try to fit it into the space available here. However, it is probably material to note that load can either cause a material to change shape, which might affect performance; resist, which can build up latent stresses; or break,


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2000T TENSION CELL

usually catastrophic. It’s also useful to know that other factors can affect performance under load including temperature, age, corrosion, impact (say from supply vessels alongside an offshore structure) and level of base load which the item was designed to carry. In its ‘Structural integrity strategy 2008-2013’16 UK HSE (Health & Safety Authority) made this “proactive approach” part of its requirement. When materials do fail under load, this is usually referred to as ‘structural failure’ and is treated very seriously by authorities such as the UK HSE.

deterioration can be the result of inadequate design and construction, operational accidents (dropped objects, boat impact for example), ageing processes or a combination. The age profile of North Sea installations show that many are now [beyond] their notional design life and, hence, may be susceptible to increasing and possibly rapid deterioration. The threat is that the deterioration, from whatever cause, impairs structural integrity to a level whereby safety of the installation is threatened.” With assets at this stage, monitoring loads is increasingly important.

Monitoring Load and Stress is a Requirement

What is used to Measure and Monitor Loads?

Those are the risks, and the challenge for engineers is to deploy the means to minimise those risks; to offer operators some indication of when things might be going wrong, including when loads and stresses change. The UK HSE, again, is specific in its requirements in this respect. For instance, on the matter of mooring17, “The duty-holder should measure and record mooring line tensions. Where this is not practicable then suitable arrangements should be in place to verify the integrity of the mooring system… These arrangements should be appropriate for the detection and confirmation of a mooring line break at the earliest practicable opportunity.” Measurement and monitoring are viewed by agencies such as UK HSE as key elements in any asset management programme. In that context, monitoring of loads and stress fit into the overall condition monitoring because a material’s behaviour under load and/or stress will vary according to its condition and its age (see above). As more structures and equipment are subject to life extension programmes, so such monitoring becomes increasingly important. To use the HSE’s own words18, “Damage and

The measuring and monitoring of loads and stresses today relies on load cells. A load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured. The various types of load cells include hydraulic load cells, pneumatic load cells and strain gauge load cells.19 With a strain gauge, the gauge is attached to the structure or component being monitored so that any change in shape caused by load or stress will cause a change in electrical resistance in the strain gauge which can then alert operators. Load cells can consist of anything between one and four strain gauges, depending on the job to be done. In any offshore operation there will be a high degree of hazard and consequent risk to be managed as part of the process. These days, while hazard and risk are better understood than ever before, the notion that their consequences in terms of cost or human life are simply part of the process is not acceptable. Therefore, it is incumbent on any offshore operator to put in place the very best available systems to maintain integrity and safety. Measuring loads and stresses is a key part of that.

Protect your assets

Hull Stress Monitoring Systems Provides access to the vessel’s real-time structural integrity as a result of wave or cargo induced static and dynamic loading.

www.strainstall.com T: +44 (0)1983 203600 E: enquiries@strainstall.com

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References: BP ‘Energy Outlook 2035’ http://www.bp.com/en/global/corporate/press/press-releases/energy-outlook-2035.html

1

2

Petrofac http://www.petrofac.com/media/47338/Petrofac_Market_factsheet_090913_LOW_RES.pdf

3

Douglas-Westwood, ‘World Subsea Hardware Market Forecast 2014-2018’

http://www.douglas-westwood.com/shop/shop-infopage.php?longref=1373#.VHNWcPmsXAk 4

Offshore Technology http://www.offshore-technology.com/features/featurerisky-business-deepwater-drilling-north-sea/

5

The Journal of Petroleum Technology

http://www.mydigitalpublication.com/article/Offshore+Oil+and+Gas+Installation%E2%80%94Aging+and+Life+Extension/951953/0/article.html 6

Offshore Technology, ‘Tieback Time’ http://www.offshore-technology.com/features/feature1033/

7

How Stuff Works http://science.howstuffworks.com/environmental/energy/offshore-drilling.htm/printable

8

The Journal of Petroleum Technology

http://www.mydigitalpublication.com/article/Offshore+Oil+and+Gas+Installation%E2%80%94Aging+and+Life+Extension/951953/0/article.html 9

Results from monitoring and assessment of offshore wind turbines http://www.eurodyn2011.org/papers/MS25-382.pdf

10

Wikipedia http://en.wikipedia.org/wiki/Offshore_construction

11

OGP http://www.ogp.org.uk/pubs/434-13.pdf

12

PhysicsNet http://physicsnet.co.uk/a-level-physics-as-a2/materials/stress-strain/

13

LETS Global http://lets-global.com/offshore-inspections/

14

UK HSE http://www.hse.gov.uk/offshore/degradation-deterioration.htm

15

University of Bolton AMI http://www.ami.ac.uk/courses/topics/0123_mpm/

16

UK HSE http://www.hse.gov.uk/offshore/integrity.htm

17

UK HSE http://www.hse.gov.uk/offshore/infosheets/is4-2013.pdf

18

UK HSE http://www.hse.gov.uk/offshore/degradation-deterioration.htm

19

Wikipedia http://en.wikipedia.org/wiki/Load_cell

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