RPR-240 TSJ Feasibility Assessment Report for FPSOsFPSOs that may not actually be the case. On a...

Document No: RPR-240

Document Title: TSJ Feasibility Assessment Report for FPSOs

Customer: -

Project: -

RTI Job No: -

REV NO REV DATE DESCRIPTION AUTH

0 9/12/2017 Initial Release ER, MF, CC

The information contained in this document is proprietary and confidential. Dissemination or distribution of this information is prohibited without written consent from Arconic Energy Systems.

DOC NO: RPR-240 REV: 0 DATE: 9/12/2017 PAGE: 2 of 32

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The information contained in this document is proprietary and confidential. Dissemination or distribution of this information is prohibited without written consent from RTI Energy Systems.

TABLE OF CONTENTS

1 INTRODUCTION ..................................................................................................................... 3

1.1 COMPANY BACKGROUND ............................................................................................ 3 1.2 EXECUTIVE SUMMARY .................................................................................................. 4

2 TSJ HISTORICAL REVIEW .................................................................................................... 4 3 TSJ PRODUCT DESCRIPTION .............................................................................................. 8 4 TSJ DESIGN METHODS ........................................................................................................ 9 5 TSJ MANUFACTURING FEASIBILITY .................................................................................12

5.1 DISTRIBUTION OF STEEL RISER PIPE SIZES ............................................................12 5.2 DISTRIBUTION OF TSJ SIZES ......................................................................................14 5.3 THICK SECTIONS IN TITANIUM GR23/29 BASE METAL .............................................16 5.4 THICK WELDS IN TITANIUM GR23/29 ..........................................................................17

6 TSJ QUALIFICATIONS DATABASE .....................................................................................18 7 TSJ GALVANIC DESIGN AND CATHODIC PROTECTION ..................................................18 8 TSJ CHEMICAL COMPATIBILITY ........................................................................................19

8.1 TITANIUM COMPATIBILITY WITH PRODUCTION FLUIDS ..........................................19 8.2 TITANIUM COMPATIBILITY WITH COMPLETION FLUIDS ...........................................19

9 TSJ INSTALLATION ..............................................................................................................21 10 TSJ MOUNTING OPTIONS FOR FPSO ................................................................................23

10.1 MOUNTING OPTIONS FOR SPREAD MOORED FPSO ................................................23 10.2 MOUNTING OPTIONS FOR TURRET / BUOY FPSO ....................................................24

10.2.1 OPTION A - RISER GUIDE TUBE W/ FIXED CONNECTION ................................24 10.2.2 OPTION B - RISER GUIDE TUBE W/ ROTATING CONNECTION ........................28

11 CONCLUSION .......................................................................................................................30 12 REFERENCES .......................................................................................................................30 APPENDIX 1 ...................................................................................................................................31


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1 INTRODUCTION

1.1 COMPANY BACKGROUND Arconic Energy Systems (“AES”), formerly RTI Energy Systems, Inc., has deep oil and gas roots, contributing to the success of our customers for over 25 years. AES provides innovative solutions for the recovery of ultra-deep, high pressure, high temp & sour service reservoirs. Our titanium and aluminum engineered products incorporate advanced design & manufacturing technologies to solve tough deepwater challenges. RTI Energy System’s former parent company RTI International Metals (“RTI”) first entered the energy market in the early 1990’s by supplying titanium casing for geothermal power plants. Recognizing the importance of titanium to the global energy market, RTI invested in a dedicated business unit with a focus on titanium product development. RTI Energy Systems soon supplied the world’s first all titanium drilling riser, titanium drill pipe and titanium stress joints. During this time RTI developed and qualified an enhancement of the workhorse 6Al-4V alloy (ASTM Grade 5) now known as 6Al-4V-0.1Ru-ELI (ASTM Grade 29) which offers a superior combination of strength, fatigue and corrosion resistance. Grade 29 has become the energy industry's titanium alloy of choice for deepwater riser applications. RTI was acquired by Alcoa in 2015 shortly before Alcoa separated into two publicly traded companies – Alcoa and Arconic - in 2016. Arconic retained all businesses related to making product, including RTI Energy Systems, now renamed Arconic Energy Systems. The products, people and assets RTI became known for are today a significant contributor to Arconic’s success. A major advantage in our line of titanium products is our vertical integration. Arconic is the only titanium company capable of controlling the entire supply chain - from melting the titanium alloys thru forging, machining, welding and assembling the final products. In addition to our operations team, we employ in-house product engineers, project managers, supply chain managers and a field service team to support the installation of our products offshore. No other titanium company has this bench strength supporting their products. To learn more about our full range of products and services please visit us on the web at www.arconic.com


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1.2 EXECUTIVE SUMMARY Titanium Stress Joints (TSJs) are a critical component for connecting deepwater risers to host facilities, subsea wellheads and other fatigue sensitive flowline terminations. These highly dynamic terminations often challenge riser engineers, particularly when they must withstand high pressure, elevated temperature and even sour service conditions. Titanium’s high strength, low weight, superior fatigue performance and excellent corrosion resistance allow TSJs to thrive in the most arduous deepwater production environments. TSJs have been used predominately in the Gulf of Mexico (GoM) deepwater region, attached to a variety of host platforms including SPARs, TLPs and SEMIs. The GoM region has very few FPSOs and as a result TSJs have not been deployed on FPSOs to date. However, there is a strong interest among our customers for using TSJs on FPSOs in other deepwater regions around the world. This report will provide an overview of our TSJ product line and present concepts for expanding the use of TSJs onto FPSOs.

2 TSJ HISTORICAL REVIEW

AES has delivered over 100 TSJs, with some in continuous deepwater service for 20 years. TSJs are currently in operation on steel catenary risers for production, water injection, gas lift, oil export and gas export risers ranging in size from 4 to 20 inches, pressures up to 15ksi, temperatures up to 250F and water depths below 7,000 feet. However, these previous project operating envelopes are not product limitations. TSJs can be designed for larger diameters, higher pressures, hotter temperatures and deeper water depths. For example, 24 inch TSJs have been manufactured and installed on deepwater drilling risers. TSJs also exhibit excellent resistance to harsh sour service conditions. A full database of historical customers, projects, sizes and operating conditions is provided in Appendix 1. From this data we can plot distributions of TSJ operating envelopes from the past 20 years. These distributions are useful for comparing to expected operating envelopes for future projects. Distributions for historical TSJ water depths, maximum operating pressures and temperatures are provided in Figures 1 - 3.

Figure 1: TSJ water depth distribution from past projects provided in Appendix 1


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Figure 2: TSJ maximum operating pressure distribution from past projects provided in Appendix 1

Figure 3: TSJ max operating temperature distribution from past projects provided in Appendix 1 TSJs have not yet been deployed on FPSOs but the expected operating envelopes, provided to AES by customers with interest in deploying TSJs onto their FPSOs, fall well within the operating envelopes of our past projects listed in Appendix 1 and shown graphically in Figures 1-3. The relative size of a TSJ is a function of hull motions and riser weights. Larger hull motions and higher riser weights lead to larger TSJs. Water depth and operating pressure have an obvious impact on riser weight, but so does a riser’s configuration. A riser configuration such as lazy-wave will reduce weight. Hull motion is also important since it determines the bending moment generated at the riser hang-off. Bending moment is the primary variable in TSJ sizing. This will be explained further in a design sizing example in Section 4.


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From the data in Appendix 1 we can cross plot TSJ size (length and thickness) by hull type in Chart 1 below.

Chart 1: Cross plot of TSJ size (length and wall thickness) by hull type for production-side risers (production, water injection, gas lift) and export side risers This chart shows that TSJs are generally thicker for SEMIs than TLPs, which would be expected given SEMI motions generally produce higher bending moments than TLPs at the riser hang-off. The chart also shows TSJs for export risers are generally longer than TSJs for production side risers. This is due to export risers being larger diameter and hence stiffer, requiring a longer and more flexible TSJ. However, notice these general size patterns are not clearly distinct between hull types. The longest TSJ would be expected to be a SEMI export TSJ (higher motions and larger diameter), but notice there is a SPAR requiring a TSJ with the same length and thickness. Two currently operating TLPs actually have export TSJs longer than a SPAR export TSJ. One of the TLP export TSJs is also longer than almost all of the SEMI export TSJs. The key take-away from this cross plot is while we would expect larger TSJs to be required for FPSOs that may not actually be the case. On a prior FPSO study we sized production TSJs for a spread-moored FPSO with lazy-wave risers and the resulting TSJ sizes were smaller than most SEMI production TSJs shown in Chart 1.


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The data in Chart 1 also shows that motion profiles can vary greatly even within the same hull type. Notice the wide spread of TSJ sizes deployed on TLPs. This will be even more evident with FPSOs. Spread-moored FPSOs have much less motion than a turret moored FPSO, and in some cases less than some SEMIs. A similar example would be comparing turret and bouyed-turret FPSOs. On a buoyed-turret system the bouy detaches before major storm events. As a result the maximum motions at riser hang-off are significantly less than a traditional turret. We have sized bouy-turret TSJs in prior FPSO studies and found the TSJ sizes are smaller than some TLP production TSJs we currently have in operation. The message is hull motions and riser configurations directly impact TSJ size. Smaller motions and lighter risers equate to smaller TSJs. While TSJs have not yet been deployed on an FPSO, we have shown in prior studies that TSJs sized for certain FPSO configurations are actually smaller than TSJs currently operating on other hull types. This also means TSJs sized for the operating conditions shown in Table 1 could be well within the sizes already operating on other deepwater facilities. It depends on the motions and weights for a given combination of hull type and riser configuration. Our experience is that these combinations are vetted during the feasibility screenings a project’s concept selection phase, where customers compare hull types and riser configurations.


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3 TSJ PRODUCT DESCRIPTION

A detailed description of TSJ product technology is available in our TSJ Functional Specification RES-072 [2] and our Titanium Riser Design Guide RTR-001 [3]. A typical TSJ configuration is shown below in Figure 4. Refer to [2] for detailed descriptions of each component and their functional performance specifications.

Figure 4: Typical TSJ configuration, refer to [2] for detailed technology descriptions

The riser hang-off utilizes our patented composite cone technology to perform two functions: it primarily acts as an anti-fretting interlayer and optionally can provide electrical isolation depending on the selection of composite material. The electrical isolation option is useful when customers require the riser to be electrically isolated from the hull to prevent interference between the pipeline and the hull CP systems. While electrical isolation is a common requirement for TLPs, SPARs, SEMIs and spread-moored FPSOs; it is not always a requirement for FPSOs using turrets and bouys. Additional information for riser hang-off in turrets is provided in Section 10. The TSJ flanges are a highly customized version of the compact flange described in the Norwegian specification Norsok-L-005. These compact flanges were originally developed specifically for high fatigue risers on the Snorre TLP. For TSJs, the basic compact flange design is further modified for connecting titanium to steel, which is not covered in the original specification. By including a series of proprietary titanium specific technologies, such as specially designed titanium fasteners, these customized compact flanges are stronger than the steel riser pipe and have a longer fatigue life than the steel weld that attaches the TSJ to the riser. Thus the flanges are not a limiting part of the design in strength or fatigue. The limiting factor is the steel riser weld below the TSJ (refer to Figure 4). Customizing the compact flange also involves various treatments to allow galvanic coupling of dissimilar metals, in this case titanium to steel. Further details of the proprietary flange technologies are provided in [2].


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4 TSJ DESIGN METHODS

Like other metals, titanium is alloyed to achieve particular performance objectives for specific engineering applications. Product engineers currently have access to over 30 titanium alloys. For subsea riser systems, AES offers two alloys commonly referred to as Grade 23 and Grade 29. The primary drivers when selecting between the alloys for a TSJ are operating temperature and NACE compliance (sour service). A full description of these alloys is beyond the scope of this report, but we recommend reviewing the alloy information provided in [3]. For purposes of this report, it is convenient to note that the two alloys are completely identical and interchangeable in terms of the mechanical properties driving TSJ design. Some key mechanical properties we will use in the design example are shown below in Figure 5.

Figure 5: Key mechanical property comparisons between titanium and other common metals

Three of the properties shown in Figure 5 comprise the reason titanium is such an ideal material for stress joints; Yield Strength, Elastic Modulus and Density. Titanium is essentially twice as strong, twice as flexible, and half the weight of typical riser steels. Titanium also performs far better in fatigue, commonly providing an order of magnitude improvement in fatigue life over typical riser steels.


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These engineering advantages of titanium are best explained through a TSJ design example. TSJs are essentially cantilevered beams that carry tension, shear and moment between the riser and hull. While changes in riser tension and shear are typically small, the moment varies greatly due to relative motions of the hull and the riser, especially during storms. A TSJ free body diagram is shown below in Figure 6, notice how the moment is distributed along the TSJ taper.

Figure 6: Free body diagram of a typical TSJ attached to an SCR

The most critical variable impacting TSJ design is hull motion which directly translates to the amount of bending moment between the riser and hull. The bending moment distribution in Figure 6 shows the bending moment at any point along the taper (Maa) is a function of the riser’s moment (M) plus the riser’s tension (T) and shear (F) acting along their respective moment arms (x) and (y). One method for designing TSJs is to assume a taper compounded from a large number of short hollow cylindrical beams (i.e. finite elements) of constant internal diameter and increasing thickness along the taper. Assuming shear is negligible for preliminary sizing (this has been confirmed on past projects as a reasonable simplifying assumption) the equilibrium equation for a tensioned beam in bending is shown in Figure 7.

Figure 7: Equilibrium equation for a tensioned beam in bending with negligible shear


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From the equilibrium equation, it becomes evident that bending stiffness is the primary variable controlling TSJ size. In fact, this is why titanium makes such a smart choice for a stress joint material. Referring back to the information in Figure 5, titanium has roughly half the elastic modulus (E) of steel. Titanium also has almost twice the strength of steel, so titanium can carry the same load across a much thinner beam cross section (I). This means titanium can achieve the same radius of curvature (i.e. riser deflection angle) with a much smaller beam size than steel because the bending stiffness (EI) is much smaller with a titanium beam. A generic example comparing steel and titanium is shown below in Figure 8.

Figure 8: Generic TSJ design example comparing titanium to steel


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This example shows the benefits of titanium over steel in terms of length (76% shorter), thickness (63% thinner) and reaction moment (79% less moment into the hull structure). This example also shows the superior fatigue performance of titanium where, at the point of transition from steel to titanium in the global riser model (i.e. where the titanium and steel cross sections are the same), the fatigue life improves by more than an order of magnitude (700yrs to 9,000yrs). While these results are specific to the design conditions presented, it has been shown over many projects that a good rule of thumb is titanium will always end up being approximately 1/3 the length of steel, 1/3 the thickness of steel and impart less than 1/3 the reaction moment of steel into the hull structure under the same riser design conditions. What is not immediately clear in this design example is the additional positive impact of density. The TSJ design is already much shorter and thinner due to titanium’s strength and flexibility. Now consider that titanium’s density is almost half of steel. The total weight of the TSJ design is more than 20 times lighter than the steel design. In fact due to the large weight savings in this example titanium is the cheaper option. Titanium is generally 5 to 10 times the price of steel, depending upon the commodity markets at the time of order. Customers have also experienced tangential savings in offshore installation costs due to the shorter lengths and lighter weights of TSJs versus competitive offerings.

5 TSJ MANUFACTURING FEASIBILITY

As mentioned in Section 2, a full database of prior customers, projects, sizes and operating conditions is provided in Appendix 1. From this data we can plot histograms of prior Riser and TSJ sizes in Sections 5.1 thru 5.3. When discussing manufacturing sizes in the next three sections we are including manufacturing data from both TSJ and Drilling Riser product lines. The reason is both product lines share exactly the same material specifications, manufacturing procedures and design features (same custom compact flange designs). This is important when presenting our titanium manufacturing capabilities for TSJs. We also make titanium casing and drill pipe, but the data from those two product lines is not included below because the material specification and manufacturing processes are not the same as TSJs.

5.1 DISTRIBUTION OF STEEL RISER PIPE SIZES From the data in Appendix 1 we can see that TSJs have manufactured in sizes ranging from 4in thru 24in. The full distribution of historical sizes is shown below in Figure 9 thru 11.


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Figure 9: Distribution of riser pipe outer diameters from all prior projects in Appendix 1

Figure 10: Distribution of riser pipe wall thickness from all prior projects in Appendix 1

Figure 11: Distribution of riser pipe D/t ratio from all prior projects in Appendix 1


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5.2 DISTRIBUTION OF TSJ SIZES From the data in Appendix 1 we can see that TSJs have been deployed in lengths varying below 15 feet to more than 50 feet. The full distribution of TSJ lengths is shown below in Figure 12. Photos of typical TSJs large and small are shown in Figures 13 and 14.

Figure 12: Distribution of TSJ lengths from all prior projects in Appendix 1

The longer TSJs (> 30ft) are typically deployed on oil and gas export risers while the shorter TSJs (< 30ft) are typically deployed on production, injection and gas lift risers. It should be noted that the length distribution shown above does not represent a maximum length limit; it simply reflects what has been needed for prior projects. The practical length limit for a TSJ is a function of highway shipping from our shop to a shore base. We estimate our maximum allowed shipping length at 200ft for highway travel (we have road shipped 180ft long steel riser components previously). If a TSJ longer than 200ft would ever be required we could deploy our titanium welding equipment and personnel to a shore base to fabricate TSJs in the range of 400ft or longer if required.


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Figure 13: Typical large TSJ commonly used for export SCRs

Figure 14: Typical smaller TSJ commonly used for production, injection and gas lift SCRs


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5.3 THICK SECTIONS IN TITANIUM GR23/29 BASE METAL Another frequent question is how thick we can make TSJs, especially at the top of taper. A distribution of TSJ D/t ratios from the top of taper is provided in Figure 15. This distribution shows a much lower D/t range than shown for the riser pipe in Figure 11, which confirms TSJs are much thicker at the top of taper than at the riser pipe. Refer to the listing of [Base WT] in Appendix 1, which are the actual top of taper wall thicknesses from all prior projects.

Figure 15: Distribution of TSJ taper maximum D/t ratios from all prior projects in Appendix 1

In fact, the thickest cross section in a TSJ is not at the top of taper, but rather in the hang-off cone and flange cross sections. A distribution of maximum TSJ wall thickness is provided in Figure 16, which shows most TSJs have a maximum thickness in the range of 4in to 8in.

Figure 16: Distribution of TSJ maximum wall thickness from all prior projects in Appendix 1

From experience with prior studies we expect these wall thickness ranges to apply equally well to the TSJ sizes that will be developed for FPSO projects. However, these thickness ranges are not hard limits; we can produce TSJs in thicker sections when required. To explain this in more detail we have included a few paragraphs explaining the fundamental differences between steel and titanium metallurgy that allows titanium to be produced in sections much thicker than steel.


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Steel subsea riser components typically rely on a tempered martensite (i.e. quench and tempered) metallurgical condition to achieve the best balance in strength and fracture properties. Since formation of the intermediate martensite phase is highly cooling rate dependent, increasing component wall thicknesses tend to promote both non-uniform and reduced core strengths in heavier section steel components. As such, thicker (e.g., >2in) tempered steel components tend to exhibit substantial property gradients with decreasing strength toward the section center. This phenomenon is further exacerbated by reduced deep hardenability in the lower carbon-equivalency steel riser pipe grades when weldability is required; and particularly with the low nickel-containing steel grades needed for sour service. In contrast to most of the riser steels, strength and fracture properties in Grade 23/29 titanium are not derived from tempering and aging treatments. Strength in these alloys instead stems primarily from a combination of substitutional alloying (i.e. Al and V additions) and interstitial (O, N) strengthening. These components are processed to achieve a stress relieved, thermally stable two phase (alpha-beta) structure involving a fully transformed-beta (acicular-alpha) microstructure which provides maximum fracture resistance for this metallurgy. Along with a very high degree of chemical homogeneity and relatively consistent grain size, this titanium alloy metallurgy results in minimal property directionality (i.e. near isotropic) and low property variation through the component’s cross section.

5.4 THICK WELDS IN TITANIUM GR23/29 Of the total TSJs produced by AES, over 85% are welded. AES has used the same procedure for all titanium welds. A total of six production qualification records (PQRs) have been performed on this procedure. The PQR reports can be made available for in-person review at our Houston office. Titanium welds using our procedure can be produced in very thick sections. In fact the limitation on weld thickness is not the ability to make the weld itself, but rather the limit is the ability to perform NDE on the weld to confirm acceptable flaw sizes are properly detected. Further details on the NDE techniques and their practical limits are provided in our TSJ ECA Design Specification RES-070 [4]. Most TSJs have multiple welds along their length, but the thickest weld is of most interest. Appendix 1 contains a list of maximum weld thickness for every TSJ. A distribution of the maximum weld thickness for every welded TSJ is provided below in Figure 17.


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Figure 17: Distribution of TSJ maximum weld thickness from all prior projects in Appendix 1

This data is only for TSJs currently in service per the data listed Appendix 1. It does not include other customer qualifications on thick titanium welds. Back in 2010 a major multi-year, multi-million dollar qualification effort was jointly was funded by ExxonMobil, Statoil and Petrobras to certify TSJs for use in their future projects. This joint effort successfully concluded last year. Expanding the weld thickness envelope to 4 inches was one of many successful qualification efforts performed under this large program.

6 TSJ QUALIFICATIONS DATABASE

AES has been supplying TSJs for over two decades and the available qualification data is quite extensive. A qualification matrix summarizing the full database is available for review [5]. The extensive qualification reports are mix of both public and confidential data. Therefore, we encourage new customers to meet with our team to review the qualification matrix and related reports. These meetings can be concluded in as little as a few days to as many as a few weeks depending on the customer’s level of interest. Due to the large amount of qualification data available to review, we can support meetings either in person or remotely online (or both) to make it easy for customer’s subject matter experts to review the information in a convenient manner.

7 TSJ GALVANIC DESIGN AND CATHODIC PROTECTION

Titanium is extremely corrosion resistant by means of a tenacious and protective natural oxide layer resulting from its reactive metallurgy. By itself, titanium would remain virtually corrosion free for far longer than the service life of a subsea riser. Two important considerations when deploying TSJs into a subsea riser system are the riser’s cathodic protection system and galvanic coupling of dissimilar metals, in this case titanium and steel. Titanium is near the top of the galvanic chart (more noble, less active) and will always be the cathodic member when coupled with more active (less noble) metals like steel in an electrolyte such as seawater. Galvanic currents will flow between the anodic steel and the cathodic titanium. This galvanic current flow results in corrosion on the surface of the steel and formation of hydrogen on the surface of the titanium which presents a concern for hydrogen embrittlement.


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The good news is negligible hydrogen absorption occurs into titanium at free corrosion potentials when connected to steel in ambient seawater. However, this changes when cathodic protection (CP) from impressed current or sacrificial anodes is used to minimize corrosion of the external steel riser surfaces. A TSJ is electrically conductive to the steel riser being protected by the CP system. When titanium is charged by the CP system, at typical cathodic potentials, hydrogen absorption and embrittlement can occur over long time periods. Therefore, to prevent hydrogen absorption, a non-conductive rubber barrier is applied to all external surfaces of the TSJ to prevent cathodic charging on the titanium surfaces. This resistant, non-conductive barrier has low water permeation and absorption rates and shields the external surface of the titanium from the electrolyte (seawater) to prevent hydrogen absorption. The rubber barrier also eliminates galvanic corrosion of the steel components mated to the TSJ. Although internal riser surfaces are not exposed to CP system charging concerns, galvanic effects arising from dissimilar metal contact still need to be considered. If produced well fluids allow the selection of carbon steel, direct galvanic coupling of titanium to the steel generally does not present a compatibility concern. If produced well fluids require the selection of corrosion resistant alloys (CRAs), either as overlays or solid pipe, then there are no compatibility issues. This compatibility stems from the similarity in corrosion potential of passive Fe-Ni-Cr-Mo and Ni-Cr-Mo alloys to those of titanium alloys in these fluids. A further description of the galvanic treatments designed into TSJs is provided in our design guide RTR-001 [3]. We recommend subject matter experts interested in this topic not only review the information in [3] but to also request a meeting with our team to discuss the concepts in more detail.

8 TSJ CHEMICAL COMPATIBILITY

8.1 TITANIUM COMPATIBILITY WITH PRODUCTION FLUIDS Titanium is highly corrosion resistant to seawater and produced well fluids such as hydrocarbons, NaCL brines, organic acids, CO2, H2S, elemental sulfur and liquid mercury. For general guidelines on produced fluid resistance of TSJs refer to RTR-001 [3]. We recommend subject matter experts interested in this topic not only review the information in [3] but also review the ‘Corrosion Testing’ block of our TSJ Qualification Matrix [5].

8.2 TITANIUM COMPATIBILITY WITH COMPLETION FLUIDS Titanium is also compatible with the vast majority of commercial injected well chemicals. These chemicals include steel corrosion inhibitors (e.g., all nitrogen- or amine-based types), glycol-based hydrate inhibitors, scale inhibitors, paraffin inhibitors, emulsion inhibitors, and pour-point depressors. For general guidelines on completion fluid resistance of TSJs refer to our TSJ Completion Fluid Compatibility Guide RTR-003 [6]. We recommend subject matter experts interested in this topic not only review the information in [6] but also review the ‘Corrosion Testing’ block of our TSJ Qualification Matrix [5]. As described in [6], additional precautions should be employed when injecting hydrochloric (HCL) acid and methanol (MeOH) containing solutions. The mitigation strategies described in [6] for


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MeOH and HCL compatibility are well established and field proven for many years across our entire customer base. Well stimulation with hydrofluoric (HF) acid has become a popular request among our customer base, especially after the oil price collapse in late 2014. Unfortunately, titanium alloys exhibit elevated corrosion rates when exposed to HF solutions at any significant concentration. AES maintains our historical position that TSJs should never be exposed to fresh, unspent HF-containing stimulation fluids being injected into a well thru the TSJ. They should instead be injected by means that bypass the TSJ and SCR such as drilling or workover vessels or the newer low cost coiled tubing vessels which can support HF injection directly into the subsea tree. While direct injection of fresh HF acid through a TSJ must be avoided, it is possible to chemically inhibit the returning spent HF acid. This has recently become important to customers interested in deploying HF stimulation thru the newer low cost coiled tubing vessels because those vessels can inject but not recover the stimulation acid. In this case, the returning spent HF acid has to flow back through the SCR and TSJ to make the coiled tubing vessels a cost-effective alternative to traditional drilling and work-over vessels which can inject and recover directly from the subsea tree. In response to strong customer interest, our research department developed and qualified a suite of chemical inhibitors for this purpose. Successful laboratory testing has demonstrated that salts of molybdates, aluminum, and borates are effective inhibitors for titanium in dilute HF solutions. Multiple customers are currently engaged with our research department in laboratory and field qualification testing of these inhibitors and results are very promising. We recommend subject matter experts interested in further details refer to our published TSJ HF Guidance [8] and to meet with our team to review the ongoing qualifications.


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9 TSJ INSTALLATION

TSJs have been successfully installed by S-Lay, J-Lay and Reel methods. S-lay has been performed successfully with TSJs installed both first-end and last-end. J-Lay and Reel methods are basically the same relative to the TSJ, since the TSJ is not spooled. For S-lay, TSJs are easier to install first-end where loading is minor. For S-lay last-end the TSJ experiences higher loading and may require an installation shroud which is described in [9]. All of the major contractors have TSJ installation experience; Technip, Subsea7, Saipem, Allseas, Helix and Herema. Refer to Figure 18 for some installation examples. Refer to [9] for further details on TSJ installation.

Figure 18: Photos from recent TSJ installations

TSJs can be laid down and parked on the seabed for extended periods. On prior projects, some TSJs have remained on the sea bed in the Gulf of Mexico for longer than 6 months in water depths below 5000ft. Figure 19 shows a recent example of a TSJ resting on the seafloor prior to recovery and hang-off.


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Figure 19: Photo of a TSJ resting on the seafloor at ~5500ft water depth

After recovery from the seafloor, risers are hung from the hull by landing the TSJ in a riser porch. Details on the riser porch are provided in the next section. A key consideration in hang-off operations are the winch control lines used to pull and steer the riser into the porch. All TSJ installations performed to date have used two control lines; one to pull the TSJ into the porch and another to steer the TSJ laterally as it arrives into the porch. Lateral steering winches are not always used when installing other top termination systems but they are important for TSJ installations due to the relatively tight fit between the TSJ and the riser porch. Figure 20 shows some examples of TSJ hang-off operations showing both pull-in and steering control lines.

Figure 20: Photos from recent TSJ installations showing the use of both pull-in and steering lines


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10 TSJ MOUNTING OPTIONS FOR FPSO

10.1 MOUNTING OPTIONS FOR SPREAD MOORED FPSO TSJ mounting for spread moored FPSOs would use the same AES Adapter Bushing technology currently deployed on TLPs, SPARs and SEMIs. Refer to [2] for further details on the Adapter Bushing. Hull contractors weld the Adapter Bushings into their porch structures as shown in Figure 21. Various examples of porch structures from recent projects are shown in Figure 22.

Figure 21: TSJ mounting option using AES standard Adapter Bushings

Figure 22: Photos of riser porches on projects using standard TSJ Adapter Bushings


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10.2 MOUNTING OPTIONS FOR TURRET / BUOY FPSO The field proven steel SCR mounting technologies recently deployed on FPSOs will work equally well with TSJs. We discuss this below as Option A, and we include a few variants of the concept. For Option B we describe another field proven technology which has been deployed for mounting steel SCRs into guide tubes on SPARs.

10.2.1 OPTION A - RISER GUIDE TUBE W/ FIXED CONNECTION Steel SCRs have been recently deployed on FPSOs using turrets with riser guide tubes. Those projects use either flexible joints or steel stress joints mounted rigidly inside the riser guide tube. Riser tension is carried on a landing shoulder at the top of the tube. Shear and moment are reacted at the bottom of the tube using a cylindrical journal sleeve that reacts rigidly (no rotation) into the lower end of the tube. The riser guide tube then reacts these loads into the turret structure. TSJs can be deployed using this very same field proven technology. The methods for reacting tension, shear and moment into the riser guide tube remain the same. TSJs would react slightly more moment into the structure than a flexible joint, but much less moment than the steel stress joints currently deployed (80% less per the design example provided in Section 4 above). Given that both flexible joints and steel stress joints are currently in operation on turrets, we do not foresee any major issues deploying TSJs. A variety of Option A concepts are provided below in Figures 23 thru 25. The common design feature is they all react both shear and moment into the lower end of a riser guide tube (Option B on the other hand will not react moment, only shear).


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Figure 23: Option A (Version 1)

Option A (Version 1) Description: The TSJ is centralized within the guide tube using a steel journal (yellow) and shrink fit steel journal sleeve (green). The riser is attached below the TSJ using our field proven proprietary compact riser flanges deployed on all existing TSJs. The steel journal is flanged above the TSJ using a larger compact riser flange designed to withstand the higher bending loads at this location. Electrical continuity can occur between the riser and turret. As an option the journal sleeve can be made integral to the journal if material thickness permits. However, separating the journal and journal sleeve offers an added advantage in isolating the pressure containing member from potential wear damage. Any wear damage in the journal sleeve would be limited to the sleeve and not progress into the pressure containing journal.


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Option A (Version 2) Description: The TSJ is centralized within the guide tube using a shrink fit steel journal sleeve. AES field proven proprietary compact riser flanges are used at the top and bottom of the stress joint. Electrical continuity can occur between the riser and turret. Version 2 and 1 are similar except for the placement of the upper titanium-to-steel flange:

Version 1 places this flange below the journal sleeve, similar to existing flexible joints

currently deployed on FPSOs such as the BC-10 project.

Version 2 places this flange above the journal sleeve, similar to existing steel stress joints currently deployed on FPSOs such as the Stones project.


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Option A (Version 3) Description: The TSJ is centralized within the guide tube using dual steel centralizer bushings that are bolted around the TSJ. AES field proven proprietary compact riser flanges are used at the top and bottom of the stress joint. Electrical continuity will not occur between the riser and turret due to composite isolation sleeves between the TSJ and bushings. Version 3 is functionally similar to version 2 except for electrical isolation from the turret:

Version 3 is presented with our patented technology for riser isolation where customers generally want separate CP systems for hull and riser protection. The composite isolation sleeves are the same patented and field proven technology we deploy on all of our standard TSJs (described in Section 3).

Currently deployed flexible joint and steel stress joint systems do not isolate the risers from the turret, and therefore Version 1 or Version 2 offer matching solutions to what is in the field on those projects.


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10.2.2 OPTION B - RISER GUIDE TUBE W/ ROTATING CONNECTION SCRs have also been successfully deployed into SPAR riser guide tubes using a double tapered steel stress joint with a rotating ball centralizer. This concept could also be deployed on FPSO turrets with riser guide tubes. The concept is similar to the fixed connection described above except the ball centralizer rotates, transmitting only side load and no moment. The moment is reacted by the deflection of the double tapered stress joint. This concept requires more space in the turret than Option A because the double tapered stress joint needs room to deflect (consider an archer pulling a bow; the bow needs space to deform). SPARs are larger and longer than a typical FPSO turret so this concept has worked well for those projects. This concept is shown below in Figure 26 and 27.

Figure 27: Photos of AES rotating ball centralizer being installed in a SPAR riser guide tube


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Figure 27: Option B

Option B Description: The double tapered titanium stress joint is centralized within the guide tube using a rotating ball centralizer. This centralizer is comprised of a steel ball shrunk-fit onto the stress joint, a centralizer sleeve and composite bearings. The composite bearing material interfaces with an alloy 625 surface on the ball to control wear during rotation of the stress joint.


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11 CONCLUSION

This report provides an overview of our TSJ product line and describes TSJ applications on FPSOs. The report begins with a summary of historical TSJ deployments over the past 20 years on similar hull types (TLPs, SPARs, SEMIs) as well as the range of sizes and operating conditions covered in those fields. Details on how TSJs are designed and manufactured were then presented along with practical limits and how those stack up against expected FPSO requirements. Finally, methods are given for mounting TSJs onto FPSOs in a variety of configurations for both spread-moored and turret types. Further references and AES engineering guides are provided below.

12 REFERENCES

Latest Revisions Unless Otherwise Noted [1] *redacted* [2] RES-072 - RTI TSJ Functional Specification [3] RTR-001 - TSJ Design Guide [4] RES-070 - TSJ ECA Design Specification [5] TSJ Qualification Matrix and Data Reference List [6] RTR-003 - TSJ Completion Fluid Compatibility Guide [7] RES-057 - TSJ Sizing Datasheet and Chemical Compatibility Table [8] AES Guidance on TSJ Exposure to Hydrofluoric Acid Containing Well Fluids [9] RTR-005 - TSJ Best Practices and Lessons Learned


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APPENDIX 1


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RPR-240 TSJ Feasibility Assessment Report for FPSOsFPSOs that may not actually be the case. On a...

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Transcript of RPR-240 TSJ Feasibility Assessment Report for FPSOsFPSOs that may not actually be the case. On a...