Community Research and Development Information Service - CORDIS

FP7

CERASPHERE Report Summary

Project ID: 606331
Funded under: FP7-SME
Country: United Kingdom

Final Report Summary - CERASPHERE (Development of a Low Cost Ceramic Buoyancy Sphere)

Executive Summary:
Oil and gas exploration is being carried out in ever deeper water, as more readily-exploitable reserves become depleted. And whilst previously uneconomical deep-water oilfields are now becoming financially viable, accessing them remains difficult due to the technical challenges associated with extreme operating conditions. Nevertheless, ultra deep-water reserves are highly attractive, accounting for 41% of new reserves discovered between 2005 and 2009: these reserves represent a market niche and the exploitable opportunity for CeraSphere.
The project has developed a novel, coated ceramic sphere that will be used to impart neutral buoyancy to components used in ultra-deep-water oil and gas exploration. This will be achieved through the development of new elastomeric resin-coated ceramic spheres that have greatly improved wall strength, as compared to the existing EPS sphere technology. Optimal sizing and spacing of the spheres will be determined by modelling activities involving buoyancy and packing efficiency. These new spheres – with enhanced compressive properties – will then be packed and cast within epoxy resin to produce the buoyancy unit – a syntactic foam containing macro-spheres.
When working in deep-water at depths of up to 5,000m the water pressure is above 500 atm. Components and systems for extracting oil and gas need to be neutrally buoyant, in order to maintain them in the desired position. Buoyancy modules for drill risers used in oil and gas exploration lines are currently made from syntactic foams using micro-spheres (up to ~2,000m) and macro-spheres (up to ~3,000m). Macro-spheres offer buoyancy advantages, but become increasingly unreliable at greater depths, owing to manufacturing inconsistencies. A typical deep-water buoyancy module will contain thousands of tightly packed spheres, and when a buoyancy module fails this can necessitate costly repairs (€100s of thousands plus considerable lost production costs) and lead to environmental harm.
Buoyancy units are a relatively mature technology, but new products are still brought to the market on a regular basis especially as oil and gas exploration is moving into new territories which require greater exploration depths.
In order to ensure that the SMEs’ commercial needs were adequately addressed a state of the art review has been carried out reviewing the performance specifications for the buoyancy unit, review of appropriate ceramic materials and candidate binder systems.
Initially we reviewed the materials (ceramics and binders) for making the spheres and guided by Trelleborg we produced a specification document determining the sphere hydrostatic compressive pressure (HCP) requirements at different depths.
Ceramic materials have been developed for sintering at a range of different temperatures (1200 - 1600°C). Selected formulations were tested by Trelleborg and from the results formulations were chosen for going forward.
Sacrificial moulds made from different materials have been made using injection moulding and polymeric materials however none of these proved viable. A number of different pulp materials were tested and although they assisted the casting process none game the desired result for the CeraSphere. The consortium then went to the contingency material and produced spheres from plaster moulds. These were not sacrificial but allowed quality spheres to be produced.
A biaxial-rotational manufacturing machine was developed during the project that allowed multiple spheres to be manufactured at the same time. This machine can be up scaled post project to allow faster manufacturing rates.
Due to the requirements for producing the buoyancy units a coating was chosen. The consortium have decided that due to cost and increased production time in applying the coating this will only be used if a suitable buoyancy chamber filling technique that doesn’t cause the spheres to shatter.
Mathematical modelling has been carried out to determine the optimum size(s) of the ceramic spheres to achieve the best packing density available. The modelling work has determined the stacking structure and the optimum balance between void density in the matrix (i.e. loading of spheres), compressive strength of the matrix, and buoyancy of the final system.
CeraSpheres covering the sintering range (1200 - 1600°C) have been produced with the correct buoyancy and Trelleborg have converted these into buoyancy units which were tested.
The samples of buoyancy composite were placed in a pressure vessel which was then subsequently sealed. The pressure was increased to 4350psi at a rate of 1000psi per minute. Once pressure was achieved, the pressure was maintained for 1 hour during which time the pressure and applied volume were recorded in order that hydrostatic failures could be identified.
Samples tested were as follows:
• Clay ceramic sphere composite, 2 off
• Alumina high temperature sphere composite, 2 off
• Alumina low temperature sphere composite, 1 off
All samples exhibited resistance to the applied hydrostatic pressure for the duration of the test without any noted hydrostatic event. Visual inspection of the sample following testing gave no indication of hydrostatic collapse.
A project website has been created and for further information please refer to www.cerasphere.com

Project Context and Objectives:
The EU is one of the leading suppliers of syntactic foams and distributed buoyancy units. Buoyancy units designed for shallower depths (up to 3,000m) are frequently manufactured from hollow glass micro-spheres. These are mixed under low shear condition (to avoid breakage) with a thermosetting resin composition, often based on epoxy technology. These systems are produced by manufacturers including the Cuming Corporation and Balmoral.
The hollow micro-spheres are obtained from companies such as 3M. These products are thin-walled, fragile, easily damaged during mixing and not suitable for use at depth. TBORG use a different approach. Expanded Polystyrene Styrene (EPS) spheres, typically 50mm in diameter are used as a starting point. They are coated with epoxy resin in large tumblers and this continues until the balls are evenly coated and the epoxy resin has cured. The process effectively produces a shell of epoxy resin around the EPS ball. These spheres are then packed and cast using epoxy resin into larger modules. Larger spheres offer buoyancy benefits and this technology is suitable for depths up to ~3,000m with the epoxy shell on each sphere withstanding hydrostatic loads.
The overall goal of the CERASPHERE project is the development of (high volume, low cost) technologies and manufacturing processes for producing ‘perfect’ ceramic spheres and integrating them into ordered deep-water buoyancy units.
The project will develop a novel, coated ceramic sphere that will be used to impart neutral buoyancy to components used in ultra-deep-water oil and gas exploration. This will be achieved through the development of new elastomeric resin-coated ceramic spheres that have greatly improved wall strength, as compared to the existing EPS sphere technology. Optimal sizing and spacing of the spheres will be determined by modelling activities involving buoyancy and packing efficiency. These new spheres – with enhanced compressive properties – will then be packed and cast within epoxy resin to produce the buoyancy unit – a syntactic foam containing macro-spheres. A selection of prototype spheres will be tested for performance at depth using the TBORG pressure testing facilities. It is envisaged that the successful development of these technologies and manufacturing processes will give a significant technology and economic advantage to EU companies.
Oil and gas exploration is being carried out in ever deeper water, as more readily-exploitable reserves become depleted. And whilst previously uneconomical deep-water oilfields are now becoming financially viable, accessing them remains difficult due to the technical challenges associated with extreme operating conditions. Nevertheless, ultra deep-water reserves are highly attractive, accounting for 41% of new reserves discovered between 2005 and 2009: these reserves represent a market niche and the exploitable opportunity for CeraSphere.
When working in deep-water at depths of up to 5,000m the water pressure is above 500 atm. Components and systems for extracting oil and gas need to be neutrally buoyant, in order to maintain them in the desired position.
Buoyancy modules for drill risers used in oil and gas exploration lines are currently made from syntactic foams using micro-spheres (up to ~2,000m) and macro-spheres (up to ~3,000m). Macro-spheres offer buoyancy advantages, but become increasingly unreliable at greater depths, owing to manufacturing inconsistencies. A typical deep-water buoyancy module will contain thousands of tightly packed spheres, and when a buoyancy module fails this can necessitate costly repairs (€100s of thousands plus considerable lost production costs) and lead to environmental harm.
The current technology for buoyancy modules operating reliably at up to 3km depth uses spheres made of Expanded Polystyrene (EPS) balls which are then coated with a shell of epoxy resin. The epoxy coating (shell) acts as the load bearing structure withstanding water pressure. Spheres from each batch are pressure tested and rated for performance which determines the depth at which the batch can be used. The spheres are then cast into larger structures using thermosetting resins to create the syntactic buoyancy unit. The overall process is subject to confidentiality, but it is variable in nature which causes uncertainty of performance/reliability. If a sphere fails in service, the resulting pressure wave can cause failure of other local spheres. This can lead to a ‘chain reaction’ of failures rendering the buoyancy unit inoperable. Such failures can result in breach of the drill riser.
Ceramic macrospheres rated for depths of 11km have been used in ROVs (Remote Operated Vehicles) and are discussed later, but these are very expensive with individual spheres costing upward of €500 each. They are only produced in low volumes and have very long lead times - the buoyancy module market requires millions of spheres annually.
The Project Concept
This project concerned the development of a spherical, low-cost coated ceramic macrosphere manufacturing process. The ceramic macrospheres were designed and manufactured and rated for higher compressive strength allowing use at greater depths. A further development of this project was to address the sphere contact issues as point contact between spheres can contribute to failure from stress concentrations. We propose to coat the higher strength ceramic spheres with an elastomeric resin. This should reduce stress concentrations and reduce the risk of failure via this mechanism. Our work included modelling of buoyancy unit performance to set detailed specifications and testing will be carried out to validate performance. With the support of TBORG, we had access to the facilities needed to fully validate that our new process produces spheres which can satisfy the demands of this aggressive environment.
This proposal addresses current weaknesses in the sector, creates new opportunities for our SME supply chain and TBORG will have access to improved technology, providing greater security for the oil and gas industry. The European market is under threat from inferior but cheaper competitive products (particularly from China) and this project will help to maintain European presence in these markets.
Scientific and Technological Objectives
The specific scientific objectives of CERASPHERE were:
1) To gain the knowledge needed for the development of a ceramic sphere manufacturing process delivering low cost and high production rates
2) To identify and develop ceramic formulations capable of producing a hollow ceramic macro-sphere with a compressive strength for incorporation into a modular buoyancy unit component
3) To develop a process for coating ceramic spheres with an elastomer resin to improve point loading conditions and improve reliability
The Technological Objectives were:
1) Determine the optimal sizing and spacing of spheres in the syntactic foam to achieve:
a. Maximum loading of the spheres, for improved buoyancy of the foam
b. High specific compressive strength
c. Resistant to catastrophic failure in the event of localised sphere failure
2) To develop a buoyancy unit design capable of being easily assembled to produce larger units, so as to allow for the production of distributed buoyancy units to customer-specific requirements
The Integrated Project Objective was:
To develop a novel coated ceramic sphere that will be used to impart neutral buoyancy to components used in ultra-deepwater oil and gas exploration. This will be achieved through the replacement of epoxy-coating of existing sacrificial EPS spheres with elastomeric resin coated ceramic spheres with improved wall strength. Optimal sizing and spacing of the spheres will be determined by modelling activities involving buoyancy and packing efficiency.
These new spheres – with enhanced compressive properties – will then be packed and cast within epoxy resin to produce the buoyancy unit – a syntactic foam containing macro-spheres. A selection of prototype spheres will be tested for performance at depth using the TBORG pressure testing facilities. The project will result in a pilot-scale supply chain for the manufacture of each modular buoyancy unit component, tested for proof of principle.

Project Results:
Work Progress and Achievements

WP1: Materials Selection and Product Specification
T1.1 - Task 1.1 – Review of specifications and requirements:
When working in deep-water at depths of up to 5,000m the water pressure is above 500 atm. Components and systems for extracting oil and gas need to be neutrally buoyant, in order to maintain them in the desired position. Buoyancy modules for drill risers used in oil and gas exploration lines are currently made from syntactic foams using micro-spheres (up to ~2,000m) and macro-spheres (up to ~3,000m). Macro-spheres offer buoyancy advantages, but become increasingly unreliable at greater depths, owing to manufacturing inconsistencies. A typical deep-water buoyancy module will contain thousands of tightly packed spheres, and when a buoyancy module fails this can necessitate costly repairs (€100s of thousands plus considerable lost production costs) and lead to environmental harm.
Buoyancy units are a relatively mature technology, but new products are still brought to the market on a regular basis especially as oil and gas exploration is moving into new territories which require greater exploration depths.
In order to ensure that the SMEs’ commercial needs are adequately addressed a state of the art review has been carried out reviewing the performance specifications for the buoyancy unit, review of appropriate ceramic materials and candidate binder systems.
A performance specifications for the buoyancy unit (information provided by Trelleborg) was completed in two sections:
Material specification
a) Sphere burst i.e. burst pressure, density, hydrostatic compressive pressure requirements by depth and safety factors that are assigned according to the operational depth. The project set a requirement to produce spheres that could meet the requirements for operating at 3,660 metres of sea water. To do this they had to meet the sphere hydrostatic compressive pressure (HCP) requirements of surviving 12,000 psi or 830 bar.
b) Sphere Hydrostatic Creep i.e. performance degradation
c) Water absorption
d) Coupling i.e. the sphere should form a bond with the subsequently added syntactic foam matrix to ensure that there is no movement of the spheres during operation.
Processing Requirements
e) Homogeneity
f) Impact resistance
g) Temperature resistance
Task 1.2 – Ceramic materials selection:
Empa provided a review of what needed to be considered when choosing a ceramic material for producing hollow spheres in the use of buoyancy distributed elements for the deep sea drilling, there is a list of properties that need to be taken account as shown below.
• Low density
• High compressive strength
• Good fracture toughness
• Low sintering temperature
Also for assessing the materials additional criteria must be used:
• Buoyancy: the buoyancy of the sphere with high burst pressure in deep sea to depths of 3000 m. For these criteria, material density and compressive strength play very critical roles.
• Cost: the costs and possibility for the mass production. Some materials require demanding processing conditions for manufacturing, which would be too costly or unpractical for large scale production. One of the most important parameters is the sintering temperature, since it usually determines the price of equipment and operational costs, and therefore the total cost of the CeraSphere products. (Higher sintering temperature = higher costs).
• Mechanical properties: basic materials properties that are important to the CeraSphere project are density, compressive strength, and fracture toughness. The compressive strength is the capacity of a material or structure to withstand loads tending to reduce size, which is a key parameter for evaluating the burst pressure of the CeraSphere products. The fracture toughness is the ability for ceramics to resist crack propagation. Ceramic materials are inherently brittle. The manufacturing of the buoyancy unit involves shooting thousands of spheres into a large mould in which there is a risk of the spheres cracking. This property is very important to the CeraSphere project for their subsequent handling of ceramic spheres at Trelleborg. A material with low fracture toughness could be too fragile to be handled and may result in damaged spheres, which consequently deteriorate the reliability and performance of the buoyancy modules.
A number of suitable ceramic materials have been selected and the following proposals were presented to the beneficiaries which were agreed:
a) High temperature ceramics (1400°C - 1600°C), will be investigated by Empa concentrating on alumina, alumina with additives and fused silica.
b) Low temperature ceramics (1300°C) will be investigated by MatRI with formulations based upon Porcelain, Bone China and Fireclay
However it was agreed that this does not preclude other materials being investigated.
Task 1.3 – Candidate binder systems
In addition to the choice of ceramic material the manufacturing process is also key to the product properties achieved. Each stage from powder, to forming, to sintering can affect the microstructure of the ceramic and therefore can significantly impact on the product properties. There are a number of additives, including liquefaction agents, plasticizers and binders which can add significant value to the final product by aiding the sintering and forming processes. Thus the correct choice of additives can be as important to the final product as the raw material selection.
Binders are defined as additives to the material being agglomerated that produce bonding strength in the green and/or final product. A binder can be a liquid or solid that forms a bridge, film or matrix filler or that causes a chemical reaction. Binders can be inorganic or organic in nature and can be in either liquid or solid form.
There are four main types of binder system:
I. Matrix binders – solids or semi-solids. e.g. tar, pitch, asphalt, wax, cement
II. Film binders – act as “glues” in the ceramic system via the evaporation of water/solvent e.g. water, solutions, dispersions, powders, silicates, gel, oil, clays, starches.
III. Chemical binders – can either form multiple components which react together or react directly with the material being agglomerated itself e.g. silicates, acid, molasses, lime and lignosulfonates.
IV. Lubricants – reduce friction and induce material flow e.g. oil, glycerine, stearate and wax.
When binders are added to a material being agglomerated they can significantly improve the mechanical strength of the green ceramic body and enable it to pass through the production steps prior to firing with lower risk of damage. In addition, the use of binders in ceramic formulations can result in an increase in strength within the final, fired product. When choosing a binder for ceramic applications there are a number of characteristics which are particularly desirable:
• Minimal ash after firing
• Low temperature burn-out
• Non-abrasive
• Readily dispersible
• Non-toxic
• Inexpensive
• Promotes easy removal of the ceramic body from the mould
Ceramic formulations for slip-casting methods are capable of naturally drying to the green stage under ambient conditions. However for this project we require a rapid ‘trigger’ from the binder to allow the ceramic to cure in the preform. Greater levels of control can be achieved using “trigger” methods of promoting cure. These can include using thermal sources to controllably accelerate the removal of water from the system or by introducing binder additives that initiate cure upon exposure to stimuli such as chemical, thermal or microwave/UV radiation.
A number of binders have been identified and the most suitable will be used in the ‘slurry’ development work package (2). These will be selected based on the different forming techniques investigated during this work package and the respective properties required in the ceramic material.
Conclusion
The specification for the buoyancy device has been determined.

A number of suitable ceramic materials have been selected and both high temperature (1400°C - 1600°C) and low temperature (<1300°C) for further investigation. However this does not preclude other materials being investigated.

A number of binders have been identified and the most suitable will be used in the ‘slurry’ development work package (2). These will be selected based on the different forming techniques investigated during this work package and the respective properties required in the ceramic material.
WP2: Ceramic Material and Moulding Development
Task 2.1 – Target specification for thin walled thermoplastic (TP) spheres
6 types of thermoplastic (TP) preforms, made by Plasto, have been tested regarding to their material properties for the feasibility of the manufacturing process. The physical quality of these preforms have been examined in terms of their joining quality and mechanical ridigity. Preforms’ thermal decomposition behaviour was very critical to the manufacturing of ceramic spheres, as their pyrolysis process would affect the integrity of the ceramic spheres and their ash content could potentially contaminate the final products. Besides, the wetting properties of these preforms in contact with water-based ceramic slips was also investigated. The casting test in the use of the same slip was done in these preforms to explore their feasibility in the formation of ceramic spheres.
The notch-edge joining structure ensures the leak-free joining of TP preform and the ash content of TP preforms was generally low, which won’t be a concern to the sphere firing process with the thermal decomposition temperature of TP preforms typically in the range of 200°C – 500°C. However the TP preforms have almost zero water vapour permeability that slip remains even after a 48h rotation process at room temperature, making them impossible for the proposed ceramic sphere forming process.
Pulp preforms were tried and although these had good permeability there were problems with ash content, inner surface inconsistency, joining and cracking of the slip.
Other preforms trialed were using a polymer mesh in a core holder but again these were either too coarse allowing all the slip to pour through or zero permeability.
The consortium decided to use the contingency plan and use plaster moulds for the casting process. These were successful and alternative preforms will be trialed post project.
T2.2 Development of ceramic materials

As the project progressed two types of ceramic materials were developed according to these requirements:
• Low density
• High compressive strength and good fracture toughness
• Inexpensive raw materials and low sintering temperature
These were alumina and clay based ceramics. Both of these systems were developed. The Alumina formulations were developed with a range of sintering temperatures from 1600 - 1300°C and the clay based having a sintering temperature of 1225°C.
All of these materials met the required technical specification with the Alumina spheres exceeding the specification whereas the clay based spheres met the specification. All spheres were tested by Trelleborg.
T2.3 Development of binding system
EMPA, de Cavis and MatRI developed binder systems to be compatible with the various ceramic slurries to achieve curing and will be selected to give long term stability.
The main criteria on the final choice of the binder materials are listed below:
• Stability in the ceramic slip and forming process
• Low ash content
• Low temperature burning out or no thermal decomposition
• Improvement of green body’s mechanical strength
• Non-toxic
• Low cost
EMPA and MatRI used different binder systems to meet the demands of the casting process. A binder was identified for the clay based slip which allowed fast curing of the slip. This was used for the sphere production.
T2.4 Development of TP spheres:
A number of novel techniques were investigated to produce seamless spheres: These were: Slip casting, Casting with sacrificial preform, Dip coating with sacrificial and Spray coating with sacrificial template.
After a number of different trials the consortium decided to produce spheres using slip casting using tumbling and rotational casting.
The best results were obtained from the rotational casting using plaster moulds and this was used for the production of spheres for the buoyancy units.
WP3: Resin Coating Process Development
A technical specification for the buoyancy unit was developed in WP1 and highlighted a “filling stage” as part of the current manufacturing process for similar products. This stage involves the use of compressed air to swiftly convey polymer spheres into the buoyancy unit casing. During this process the spheres are estimated to reach velocities up to 35ms-1 and are at risk of damage from impact with the tooling, casing and each other.
Due to the brittle nature of ceramic materials, the risk of damage is significantly higher than with the polymer spheres currently used. It was therefore proposed that a protective coating is applied to the exterior of the ceramic spheres produced for the CeraSphere project.
Other considerations that were made were in relation to the potential effect the coating may have on the end-of-life buoyancy loss of the unit. There is typically a customer specified constraint of this value at between 3% and 5%, depending on customer and application specifics.
This “property” is a combination of three effects:
1. Elastic compression (due to the material bulk modulus).
2. Inelastic compression (due to hydrostatic failure of voids, macroscopic or microscopic).
3. Water absorption.
The impact of the coating on each of these effects will depend upon the material type chosen. If, for example, foam is chosen as the elastomer boundary layer this would potentially contribute to inelastic compression. Alternatively the use of polymers with high degrees of free volume could contribute to elastic compression and the presence of a “disbanded” component could increase the water absorption.
T3.2 Develop tumbling coating technique
Until the final ceramic material had been defined and a method of producing suitable spheres with optimal wall thickness determined it was necessary to perform the previous coating trials on flat alumina ceramic test parts. This allowed the coating materials to be assessed for chemical compatibility with a ceramic material and the syntactic foam element of the buoyancy unit and also allowed the impact absorption capabilities of the coatings when applied to a ceramic to be compared. However, these tests could not be used to define a quantifiable level of protection which would be provided by each coating material to a hollow ceramic sphere which may behave differently than flat substrate parts. Due to this reason a selection of candidate materials of different types were taken forward for further testing on more representative ceramic sphere substrates.
These candidate materials are all readily available, commercial products and include wet coating systems, gels/foams and nettings. These different material types all require different methods for applying them to the sphere surface.
The chosen materials were initially tested using a Ray-ran Pendulum Impact Testing System. As the primary role of the coating material is to protect the ceramic sphere from damage during the filling stage of the deep sea buoyancy unit manufacture. Therefore in order to ensure this is assessed as accurately as possible the coated spheres were tested in a way that is as representative to the current filling process as possible.
The use of a Rosand Falling Weight Impact Tester was considered as a suitable test method. This is capable of reaching velocities in the region of ~18 m s-1 and would aid in further narrowing the choice of candidate materials.
This technique however was not fully representative of the conditions the sphere encountered in the actual filling process where coated spheres would be expected to undergo some level of rebound as well as contacting with other spheres, tooling and the casing of the buoyancy unit all of which will have different material properties and levels of flexibility.
In order to make the final testing as representative as possible to the actual manufacturing process, a purpose built test rig wad developed. This mimicked the filling process but on a much smaller scale and used compressed air to propel individual ceramic spheres into a suitable container.
To accurately reproduce factory loading conditions a localised setup was required. The current system loads the spheres into the buoyancy unit with a velocity of 35 m/s. To reproduce this it was proposed that a launcher should be designed and built to meet this specification. A number of options were researched including pressure-based and elastic-based launchers. The final design was based on the principle of an air cannon.
All the coatings were tested and the choice of the final one was based on a combination of surviving the firing test, ease of application and compatibility with the syntactic foam.
WP4: Modelling of Packing of Buoyancy Unit
Task 4.1 – Determine ideal ceramic sphere size, wall thickness, mixed sizes
In order to investigate the effect of the production imperfections of the sphere, two aspects were considered: Non-uniformity of the wall thickness and parting line at the equator (parting plane) of the sphere. When 0.1 mm variation of wall thickness was considered, the minimum nominal wall thickness varied between 0.4 mm to about 0.54 mm for an operating depth range between 2500 m to 3500 m. When an equator line (groove) with a width and a depth of 0.1 mm was included in the simulation model, the minimum wall thickness increased to about 2.09 mm and 2.53 mm corresponding to the operating depths of 2500 m and 3500 m. When the sphere diameter decreased to 20 mm then, the minimum wall thickness reduced to about 0.82 mm and 0.86 mm at operating depths of 2500 m and 3500 m.
Task 4.2 – Modelling of buoyancy unit
A theoretical and Finite Element analysis of the structural performance of Alumina spheres was carried out considering operating depths from 2500 m to 5000 m. A good agreement was seen between the results obtained by the theoretical approach and Finite Element modelling.
Investigations were carried out with the following three sphere configurations:
1. Spheres with uniform wall thickness
2. Spheres with non-uniform wall thickness
3. Spheres with a parting line (groove) at the equator
The minimum thickness values obtained for the uniform and non-uniform wall thickness spheres varied by about 7% to about 12% with non-uniform spheres requiring larger wall thicknesses. The minimum wall thickness increased by about four to five times when a parting line was implemented in the FE model.
Packing density calculations were carried out assuming a simplified geometry of the buoyancy module. Using the packing density distribution, the smallest and the largest minimum wall thicknesses and syntactic foam as the matrix material, the bulk density was calculated. With the larger minimum wall thicknesses the compound density of the spheres was greater than the density of the syntactic foam. Because of this, sphere sizes corresponding to lower packing density resulted in lower bulk densities. With the smaller minimum wall thickness corresponding to a uniform ideal sphere, calculations resulted in a sphere compound density lower than the density of the syntactic foam. Here, higher packing density resulted in lower bulk densities.
Task 4.3 – Overall design of buoyancy units including packing

Analysis has been completed for the final designs of the buoyancy unit using finite element analysis. Ideal ceramic spheres of two diameters, 50 mm and 10 mm, were modelled encased in a substrate material with a packing density of 52 %. Minimum wall thicknesses of the spheres were assessed based on the Mohr-Coulomb factor at a series of depths of 1000, 2000, 3000, 3500 and 4000 MSW. From these results bulk densities and buoyancies of the final unit were calculated alongside total material requirements of the designs.

A packing density analysis showed that the packing density of the modelled system with two sphere sizes was greater than the maximum density predicted when using a single 50 mm sphere size alone; this was as expected. It was demonstrated that the choice of substrate material has a strong impact on the final design. At a depth of 3500 MSW a change of substrate from the original choice to a lower density material saw a respective drop in minimum wall thickness of 0.13 mm and 0.08 mm for the 50 mm and 10 mm diameter spheres. A 16% increase in buoyancy was calculated with this alteration. For a hollow cylinder prototype unit of 300 mm in diameter and 1000 mm in height a total of 500 x 50 mm spheres and 8000 x 10 mm spheres should be used.

WP5: Ceramic Sphere Manufacture & Elastomeric Resin Coating
Task 5.1 – Manufacture of ‘green stage ‘ceramic spheres

Empa and MATRI developed manufacturing processes to produce ceramic green spheres in a demonstration scale, respectively.

The preferred process was a bi-axial rotational casting machine with 6 sphere holders using plaster moulds. This system was used for the production of prototype ceramic spheres.

Task 5.2 – Firing of spheres

For sintering different debinding, sintering temperatures, and cycles were investigated to determine the optimal process for sintering the ceramic sphere and retaining the shape of a perfect sphere. The firing processes have been developed for both alumina-based ceramic spheres and clay ones, and were used successfully to produce the sintered ceramic spheres.

Continuous sintering was researched for post project development and a suitable system was identified that should suit both the Alumina and clay based systems.

Task 5.3 – Resin coating of spheres

A number of resins were tested for consideration of their suitability. The defined parameters were; compatibility, density, coating finish and thickness, stability, application methods, added cost and impact energy absorption.

The two best performing coatings were LDPE netting and Sorbothane® materials; however the consortium decided that only LDPE netting would be used as it gives the shortest sphere coating preparation time, can be automated and gives a consistent coating thickness.

Task 5.4 – Mechanical testing of ceramic spheres

The mechanical performance of the manufactured alumina ceramic and clay based ceramic spheres was been at Trelleborg Offshore Ltd in two ways with respect to its deep-sea application: an isostatic compressive pressure proof test and a burst pressure test. Both are industrial standard test methods and are generally considered to be the most efficient methods for validating the design of prototypes.

Alumina ceramic spheres sintered at 1600°C, 1400°C and 1300°C were evaluated regarding to the maximum compressive strength (or so called burst pressure) test. In this test, the hydrostatic pressure is applied to the test chamber until the loaded ceramic sphere is burst by the applied pressure. Not only can we reveal the maximum iso-static compressive strength of a single sphere, but also the results indicate the maximum operating depth of these spheres. The Alumina ceramic spheres sintered at 1400°C and 1600°C were evaluated and exceeded 150 MPa of burst pressure. Qualitatively, alumina ceramic spheres sintered at lower temperature generally have a slightly lower burst pressure as compared to that of the spheres sintered at 1600°C. Nevertheless, alumina ceramic spheres with both sintering temperatures are proven to achieve a depth rating of > 5000 m. The advantages of using ceramic hollow spheres are not limited to their mechanical properties. Thanks to the material stability of ceramics, the developed ceramic spheres have better temperature resistance and thus can speed up the manufacturing of syntactic foams, which is an exothermic process and currently requires a staged filling process of hollow polymer macrospheres. Overall, the developed alumina based ceramic spheres have demonstrated excellent potential as a promising replacement for hollow polymer-based macrospheres and glass microspheres for developing buoyancy modules in deep-sea offshore drilling application.

Low temperature clay based ceramic were evaluated by Trelleborg in the isostatic pressure proof test for ‘Macro Creep @ 12000 psi’ and met the required technical specification.

Conclusions

A manufacturing process for producing ceramic spheres has been identified and is feasible to be scaled up for large volume production, if automatic production manners are applied with adequate amount of plaster moulds.

Alumina ceramic spheres (50 mm in diameter, 1.0 mm wall thickness) sintered at and above 1300°C meet the burst pressure requirement (83 MPa /12000 psi) with potential for achieving even lower sintering temperatures (e.g. 1200°C). (83 MPa /12000 psi)

Low temperature clay based ceramic spheres (50 mm in diameter, 1.0 mm wall thickness) sintered at 1225°C meet the minimum burst pressure requirement 69 MPa /10000 psi)

Alumina CeraSpheres sintered at 1400°C and 1600°C achieved burst pressures above 150 MPa / 22000 psi (rating depth > 5000 msw with a 150% safety factor).

Low temperature clay based ceramic spheres sintered at 1225°C above 69 MPa /10000 psi (rating depth >3660 msw with a 150% safety factor).

WP6: Demonstration and Industrial validation

Task 6.1: Review of sphere handling and packing solutions

Spheres made of a) Clay ceramic sphere composite, b) Alumina high temperature sphere composite and c) Alumina low temperature sphere composite were made into buoyancy units.

Trelleborg after reviewing the performance of all the spheres made the decision that the smaller spheres used in their current buoyancy units were not required as the performance of the ‘CeraSpheres’ i.e. strength and buoyancy negated this requirement. As a result manufacturing was made simpler as in the current process filling is made in stages as the syntactic foam is exothermic and can destroy the polymeric spheres due to melting, this is not the case using ‘CeraSpheres’, therefore the filling process can be speeded up.

Task 6.2: Manufacture and testing of buoyancy device

Manufacture of buoyancy device

The mould tool was obtained from storage and disassembled and cleaned using degreaser, then wax was applied to the tool and Silicone release agent added to the tool. A 6mm silicone rubber seal was then added to the tool before it was assembled and preformed polypropylene discs placed in the tool.

The tool was then filled with spheres and a further polypropylene mesh placed in the chamber the closed. Pipework was then connected to the tool to allow syntactic foam to be pumped into it. When the sample buoyancy devices were prepared they then sent for analysis purposes.

Testing of buoyancy device

The pressurisation of the buoyancy syntactic composites was achieved by using a large pressure vessel connected to a universal test machine equipped with a hydraulic ram in place of “normal” uniaxial test fixtures.

The sample were placed into the test vessel and the lid fastened. The samples were then allowed to reach the test temperature; the temperature of the water was already set at this point. Air trapped at the top of the vessel was then bled away from the vessel using the valve on the top of the vessel. The universal test machine controls moves the hydraulic ram at a rate that generates a pressurisation rate in the vessel of 1000psi.min-1. The displaced volume and pressure generated are recorded continuously during the test.

The samples of buoyancy composite were placed in a pressure vessel which was then subsequently sealed. The pressure was increased to 4350psi at a rate of 1000psi per minute. Once pressure was achieved, the pressure was maintained for 1 hour during which time the pressure and applied volume were recorded in order that hydrostatic failures could be identified.

Samples tested were as follows:

• Clay ceramic sphere composite, 2 off
• Alumina high temperature sphere composite, 2 off
• Alumina low temperature sphere composite, 1 off

All samples exhibited resistance to the applied hydrostatic pressure for the duration of the test without any noted hydrostatic event. Visual inspection of the sample following testing gave no indication of hydrostatic collapse.

Task 6.3 – Overall results and assessment of market suitability

CeraSpheres covering the sintering range (1200°C - 1600°C) were produced with the correct buoyancy and Trelleborg Offshore converted these into larger buoyancy units which were tested. All finalised recipes tested successfully at Trelleborg Offshore in scaled up buoyancy modules at equal or greater than 3000 msw (Metres of Sea Water).

This project proved the proof of concept and is now ready to move to the exploitation stage.

WP7: Dissemination and Exploitation
Task 7.1 – Project website
To aid dissemination of the CeraSphere project a secure website was created in M3 of the project which gives the public information on the Project Goal, Partners, Project Objective and Press Releases. The website is located at www.cerasphere.com. The website also has a secure partner login facility controlled by individual project participant each having their own unique password. Further information and is detailed in the Project Management section of this report and the attached PDF.
Task 7.2 – Dissemination & Exploitation Plan
The interim Dissemination and Exploitation Plan has been completed and uploaded to the participant portal.

Task 7.3 – IP Protection

A patent search has been carried out both before and during the project and it was confirmed that that CeraSphere was not infringing any IP.

The consortium have decided that they would treat the results of the project as a ‘Trade Secret’ especially as the partners were bound by confidentiality for 5 years after the completion of the project as outlined in the consortium agreement.

Trademark: CeraSphere for Class 20 - Non-metallic buoys for use in the gas and oil industry, has been purchased.

An exploitation strategy has been agreed by the SME beneficiaries.

Potential Impact:
The EU is one of the leading suppliers of syntactic foams and distributed buoyancy units. Buoyancy units designed for shallower depths (up to 3,000m) are frequently manufactured from hollow glass micro-spheres. These are mixed under low shear condition (to avoid breakage) with a thermosetting resin composition, often based on epoxy technology. These spheres are then packed and cast using epoxy resin into larger modules. Larger spheres offer buoyancy benefits and this technology is suitable for depths up to ~3,000m with the epoxy shell on each sphere withstanding hydrostatic loads.
The project has developed a novel, coated ceramic sphere that will be used to impart neutral buoyancy to components used in ultra-deep-water oil and gas exploration. This will be achieved through the development of new elastomeric resin-coated ceramic spheres that have greatly improved wall strength, as compared to the existing EPS sphere technology. Optimal sizing and spacing of the spheres will be determined by modelling activities involving buoyancy and packing efficiency. These new spheres – with enhanced compressive properties – will then be packed and cast within epoxy resin to produce the buoyancy unit – a syntactic foam containing macro-spheres.
Oil and gas exploration is being carried out in ever deeper water, as more readily-exploitable reserves become depleted. And whilst previously uneconomical deep-water oilfields are now becoming financially viable, accessing them remains difficult due to the technical challenges associated with extreme operating conditions. Nevertheless, ultra deep-water reserves are highly attractive, accounting for 41% of new reserves discovered between 2005 and 2009: these reserves represent a market niche and the exploitable opportunity for CeraSphere.
When working in deep-water at depths of up to 5,000m the water pressure is above 500 atm. Components and systems for extracting oil and gas need to be neutrally buoyant, in order to maintain them in the desired position. Buoyancy modules for drill risers used in oil and gas exploration lines are currently made from syntactic foams using micro-spheres (up to ~2,000m) and macro-spheres (up to ~3,000m). Macro-spheres offer buoyancy advantages, but become increasingly unreliable at greater depths, owing to manufacturing inconsistencies. A typical deep-water buoyancy module will contain thousands of tightly packed spheres, and when a buoyancy module fails this can necessitate costly repairs (€100s of thousands plus considerable lost production costs) and lead to environmental harm.
The current technology for buoyancy modules operating reliably at up to 3km depth uses spheres made of Expanded Polystyrene (EPS) balls which are then coated with a shell of epoxy resin. The epoxy coating (shell) acts as the load bearing structure withstanding water pressure. Spheres from each batch are pressure tested and rated for performance which determines the depth at which the batch can be used. The spheres are then cast into larger structures using thermosetting resins to create the syntactic buoyancy. The overall process is subject to confidentiality, but it is variable in nature which causes uncertainty of performance/reliability. If a sphere fails in service, the resulting pressure wave can cause failure of other local spheres. This can lead to a ‘chain reaction’ of failures rendering the buoyancy unit inoperable. Such failures can result in breach of the drill riser.
This project addresses current weaknesses in the sector, creates new opportunities for our SME supply chain and TBORG will have access to improved technology, providing greater security for the oil and gas industry. The European market is under threat from inferior but cheaper competitive products (particularly from China) and this project will help to maintain European presence in these markets.

Dissemination
A project website has been developed by the partners with both public and confidential sections and is available at www.CeraSphere.eu. This was be used as the main vehicle of dissemination and interaction with the public who seek information and news about the CeraSphere project.

The project partners attended four exhibitions:
• Offshore Northern Seas, 25-27 August 2014 in Stavanger, Norway
• ETH-Zurich for Materials Science, Feb 2015 in Zurich, Switzerland
• ETH-Zurich for Materials Science, Feb 2016 in Zurich, Switzerland
• Southern Manufacturing & Electronics Exhibition, 9-11 Feb 2016 Farnborough, UK

Two publications were submitted:
• Production buoyancy at a depth of up to 5,000 metres – waters previously too deep to work in without failure. www.oilandgasconnect.co.uk/magazine May 2015 edition
• Novel hollow ceramic spheres and their mechanical characterizations http://www.mdpi.com/journal/materials which has been submitted and under review

Three press releases were sent out:
• EMPA News no. 42 (April 2014) in German and in English
• MatRI Press Release (April 2014) http://www.journalism.co.uk/press-releases/lifejackets-for-deep-sea-drills/s66/a557022/
• Project Press Release (June 2014) http://www.oedigital.com http://www.offshore-mag.com
A project leaflet and PowerPoint presentation was produced

There are two post project dissemination activities in the form of lectures are planned:
• 18th International Conference on Oil, Gas and Petrochemistry, October 2016 in Dubai, Arab Emirates
• FAC 2016, October 2016 in Slovakia

The partners have agreed to share all the IP to allow each one to exploit as they wish. The results that can be exploited are:
• Technical Targets and Materials Specifications
• Ceramic Slurry and Binder Formulation
• Thin Walled TP Sphere Technology
• Elastomeric Resin Coating System
• Buoyancy Modelling and Packing Results
• Ceramic Sphere Firing Process
• Buoyancy Modules and Performance Data

List of Websites:
www.cerasphere.com

Contacts:

Moulded Foams Ltd
John Thornberry
jrt@mouldedfoams.com

Plasto AS
Lars Stenerud
Lars@plasto.no

de Cavis AG
Urs T. Gonzenbach
urs.gonzenbach@decavis.com

Almath Crucibles Ltd
Michael Mission
michael@almath.co.uk

Trelleborg Offshore
Dave Williams
dave.williams@trelleborg.com

The UK Materials Technology Research Institute Limited MatRI)
David Cartlidge
d.cartlidge@peratechnology.com

Eidgenoessische Materialpruefungs Und Forschungsanstalt (EMPA)
Jakob Kubler
jakob.kuebler@empa.ch

Related information

Reported by

MOULDED FOAMS LTD
United Kingdom
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