Table Of ContentTITANIUM ALLOYS IN
SUBSEA AND OFFSHORE
PRODUCTION SYSTEMS
Publication 96/100
Published by MTD
The Marine Technology Directorate Limited
Registered in England No. 2022686
Registered Office:
19 Buckingham Street
London WC2N 6EF
UK
Registered as a Charity under the Charities Act 1960
Registered Charity No. 295576
0 MTD 1996
ISBN: 1 870553 25 X
(Cover Photograph: Courtesy of Conoco )
Printed by Expedite Graphic Ltd., London SWl
FOREWORD
This report results from a survey, predominantly of oil companies, to assess industry's attitude to
the use of titanium in offshore applications, and to identie whether research and development
work is needed to address uncertainties relevant to its use in this general area.
The survey was jointly funded by The Marine Technology Directorate Limited (MTD) and the
Health and Safety Executive. The work was performed under contract to MTD by Dr Carl Baxter
(Carl Baxter and Associates) and Dr Roger King (Failure Control Ltd); the Project Manager at
MTD was Mr Robert Barrett.
HSE's interests in the project were controlled by Mr Ken Woodward, and the work was monitored
by Mr James Krol of the Marine Technology Support Unit (MaTSU).
ACKNOWLEDGMENTS
Assistance in the compilation and review of material data is gratefully acknowledged from the
following:
Mr David Peacock Timet and The Titanium Information Group
Dr Reza Razmjoo The Welding Institute (TWI)
Mr Michael Gittos The Welding Institute (TWI)
Mr Ron Shutz RMI Titanium Co
Titanium Alloys Offshore (MTD 96/100) 3
CONTENTS LIST
3
FOREWORD
3
ACKNOWLEDGMENTS
8
1. SUMMARY
8
1.1 Structure of the Report
8
1.2 Research Requirements
10
2. INTRODUCTION
10
2.1 Objective
10
2.2 Methodology
10
2.3 Background
12
3. OVERVIEW OF TJTANIUM
12
3.1 History
12
3.2 Types of Titanium
13
3.3 General Problems Relating to Offshore Use
13
3.3.1 Corrosion
13
3.3.2 Hydrogen Absorption
13
3.3.3 Chemical Attack
13
3.3.4 Galling
14
3.3.5 Wear
15
3.4 Product Availability
15
3.5 Manufacturability
16
4. CANDIDATE GRADES
16
4.1 Introduction
16
4.2 Overview of Grades
19
4.3 Titanium Usage
20
5. OFFSHORE APPLICATIONS
20
5.1 Introduction
20
5.2 Topsides Equipment
20
5.3 Catenary Risers
22
5.4 Rigid Risers
22
5.4.1 Types
22
5.4.2 Structural Behaviour
23
5.4.3 Applications Suitable for Titanium
24
5.5 Xmas Tree and Export Riser Jumpers
24
5.6 Structural Stress Joints
25
5.7 General Drilling and Completion Equipment
25
5.7.1 General
25
5.7.2 Tubing
25
5.7.3 Drill Pipe
26
5.7.4 Coiled Tubing
26
5.7.5 Choke, Kill and Booster Lines
26
5.8 Subsea Production Equipment
26
5.8.1 Flowlines
4 Titanium Alloys Offshore (MTD 961100)
5.8.2 Flowline Jumpers 27
5.8.3 Manifold Piping 27
5.8.4 Subsea Valves 27
5.8.5 Umbilicals 27
6. RESULTS OF THE INDUSTRY SURVEY 32
6.1 Introduction 32
6.2 Analysis of Data 32
6.3 Results 33
6.3.1 Topsides Equipment 33
6.3.2 Drilling Riser Systems 33
6.3.3 Rigid Production and Export Risers 34
6.3.4 Catenary Risers 34
6.3.5 Completion Equipment 34
6.3.6 Subsea Production Equipment 35
6.3.7 Miscellaneous Uses 36
6.3.8 Other Applications 36
7. REVIEW OF EXISTING DATA 41
7.1 Introduction 41
7.2 Basic Material Properties 41
7.3 Corrosion Resistance 42
7.3.1 Seawater 42
7.3.2 Well and Process Fluids 42
7.4 Fatigue Resistance 43
7.4.1 Endurance (S-N) Data for Parent Unwelded Material 43
7.4.2 Endurance (S-N) Data for Weldments 43
7.4.3 Fatigue Crack Growth and Frequency Effects 44
7.5 Sour Con&tions, Stray Cathodic Currents and Hydndmg 46
7.6 Methanol Environments 48
7.6.1 Monotonic Loadmg 48
7.6.2 Cyclic Stressing 49
8. CURRENT RESEARCH dk DEVELOPMENT 54
8.1 Commercial Research 54
8.1.1 SINTEF Joint Industry Project 54
8.1.2 Bunting Titanidinningham University 54
8.1.3 Hunting Oilfield Services/SINTEF 54
8.1.4 RMI Titanium/Hydril 55
8.1.5 Stolt Comex Seaway 55
8.2 Research at British Universities 55
8.3 Other Relevant Work 57
9. RESEARCH REQUIREMENTS 58
9.1 Introduction 58
9.2 Applications and Alloys 58
9.2.1 Applications 58
9.2.2 Alloys 58
9.3 Allowable Stresses 59
9.4 Corrosion Properties 59
,Titanium Alloys Offshore (MTD 9640 0) 5
9.5 Fatigue and Fracture Properties 60
9.6 Stress Corrosion Cracking 60
9.7 Joining Processes 61
9.8 Non-Destructive Evaluation 62
9.9 Surface Treatments 62
9.10 Design Guidance for Catenary Risers 62
9.11 General Design Guidance 62
REFERENCES 63
APPENDIX 1 Questionnaire and Organisations approached 65
APPENDIX 2 Details of UK Academic Research 71
LIST OF ILLUSTRATIONS
Figure 4.1 'Family Tree' of ASTM Titanium Grades 19
Figure 5.1 Catenary Riser System 29
Figure 5.2 Rigid Tensioned Production Riser 29
Figure 5.3 Riser Tower 30
Figure 5.4 High Pressure Drilling Riser 30
Figure 5.5 Low Pressure Drilling Riser 31
Figure 5.6 Production Riser Taper Stress Joint 31
Figure 5.7 Tension Leg Taper Stress Joints 32
Figure 5.8 Coiled Tubing Unit 32
Figure 6.1 Survey Results for Topsides Systems 38
Figure 6.2 Survey Results for Drilling Riser Systems 38
Figure 6.3 Survey Results for Rigid Production & Export Riser Systems 39
Figure 6.4 Survey Results for Catenary Riser Systems 39
Figure 6.5 Survey Results for Completion Equipment 40
Figure 6.6 Survey Results for Subsea Production Equipment 40
Figure 6.7 Survey Results for Miscellaneous Equipment 41
Figure 7.1 Effect of Frequency on Corrosion Fatigue Crack Growth Behaviour
of Ti-6Al-4V in Aqueous 0.6 M NaCl 52
Figure 7.2 Fatigue Crack Growth of p Annealed Ti-6A1-4V in 3.5% Aqueous
NaCl 52
Figure 7.3 Fatigue Crack Growth of Mill Annealed Ti-6A1-4V in 3.5%
Aqueous NaCl 53
Figure 7.4 Variation of the Critical Stress Intensity Factors with Hydrogen
Content in Grade 12 Titanium Bar for Specimens with T-L
Orientation 53
Figure 7.5 Variation of the Critical Stress Intensity Factors with Hydrogen
Content in Grade 12 Titanium Bar for Specimens with L-T
Orientation 54
Figure 7.6 Effect of HC1 and Water Content on Time to Failure for
Commercially Pure Titanium 54
Figure 7.7 Effect of Frequency on Fatigue Crack Growth of Ti-662 in
MethanoVHCl Solutions 55
Figure 7.8 Effect of Chloride and Inhibitor on Fatigue Crack Growth of
Ti-662 at 5 Hz in Methanol 55
6 Titanium Alloys Offshore (MTD 96/100)
1. SUMMARY
Historically titanium has been considered as a material of last resort in the offshore oil and gas
industry because of the perception of a high initial price and service experience limited to a few
niche applications. This view is now changing due to a reduction and stabilisation in world prices
over the past few years together with the increased engineering challenges of deep water
production and high pressure, high temperature well flows.
It is evident from activity in the titanium industry and from the replies received from oil
companies during the survey reported here that there is growing interest in titanium for many uses.
It already is well established for topsides heat exchangers and companies reported no problems in
using it in this application. In Norway it is also widely used for firewater and ballast systems on
platforms and Conoco has installed the first titanium drilling riser on the Heidrun field. The
industry recognises that there are many other parts of deep water or high pressure, high
temperature systems for which the metal has potential. It is also used for coiled tubing and
downhole components, and is being developed for drill pipe sections for highly deviated wells.
Various oil company studies in the past have shown a potential benefit from using titanium for
drilling risers in deep water such as West of Shetlands and in Norway. The material is also being
studied by several oil companies as a replacement for reinforced hose currently used for catenary
production risers in conditions that preclude the use of flexible pipe (i.e. high pressure, high
temperature and/or sour fluids). As a result of the survey and recent activity in the industry, it
appears that the main interest in the near future will be to use titanium for catenary riser systems
where it is subjected to a wide range of fluids and fatigue loading.
Unlike steel and other conventional materials, which have had many years of research and
development for use in offshore oil and gas production systems, titanium is comparatively new to
the field. Steel will obviously remain the primary material for structures and piping, with other
materials finding niches. Titanium is expected to be one of these 'niche' materials.
1.1 Structure of the Report
This report begins with a brief history of titanium and some of the main factors to be considered
when using it in offshore oil and gas systems. It then looks in more detail at applications where
titanium offers advantages and presents the results of a survey amongst oil companies on their
opinions of the future use of the material.
The main grades are briefly reviewed and the most promising candidates for the various
applications are identified. The current state of knowledge of the material relevant to its use
offshore is reviewed and future research requirements have been derived.
1.2 Research Requirements
The main areas identified for research are:
Allowable Stresses: Structural grades of titanium, like high strength steels, have a high yield
to ultimate strength ratio. Current design codes specify a smaller allowable percentage of
ultimate tensile strength than yield strength (typically 50% ultimate or 67% yield whichever
is the smaller). This may be overconservative when designing with high strength materials.
It is proposed to look at the build up of safety factors in relation to the mode of failure and
reserve strength for specific applications.
8 Titanium Alloys Offshore (MTD 96/100)
Corrosion Properties: Titanium is a very corrosion resistant material but there are few
published data on the effect of well fluids at realistic temperatures and flow conditions,
particularly the effect of sand and other solids which may damage the protective oxide film at
high flow rates. Further work also needs to be done on crevice corrosion, particularly at high
temperatures, for several of the alloys.
Fatigue Properties: There is a lack of data on fatigue in representative environments for
many grades of titanium and there is conflicting data from the tests which have been
undertaken. Furthermore, most of the data is not for material in the finish or microstructure
in which it would be supplied. Better data might enable more economic production in some
cases.
Stress Corrosion Cracking: Although stress corrosion cracking is well characterised and
9
understood for some grades, the data is limited for many of them and does not examine
combined effects, of a stress corrosion cracking environment together with low amplitude
stress cycling,f or example.
Joining Processes: Titanium welding is in its infancy by comparison with steel. There is
great scope for the development of processes to reduce the cost of welding, such as plasma
arc and friction welding. Other joining methods such as screwed connection also have
potential interest.
Surface Treatment: Titanium is prone to galling. If it is to be used in some of the
9
applications identified, especially those involving threaded connections, surface treatments
must be proven and their effect on fatigue and fracture examined.
Design Guidance for Catenary Risers: Considerable interest is being shown in the use of
titanium for catenary risers and there is an immediate need for design guidance for the
industty on this subject.
General Design Guidance: Most industry codes of practice, guidance notes and
specifications do not include titanium and there is a need to include it as material in many of
these.
Titanium Alloys Offshore (MTD 96/100) 9
2. INTRODUCTION
2.1 Objective
The main purposes of the study leading to this report was to determine current and future use of
titanium offshore and to identify whether research and development work is required to address
any uncertainties relevant to its use in subsea and offshore production systems.
The questionnaire used for this survey was sent mainly to oil companies and sought to determine
the applications where titanium is already being used offshore, where it is being actively
considered, and possible future applications.
2.2 Methodology
The information for this study was gathered from manufacturers, oil companies and research
establishments as well as published material.
A questionnaire was prepared (Appendix l), principally aimed at oil companies and circulated to
46 companies in the UK, Norway and the USA. The purpose of the questionnaire was to establish
the degree of interest in titanium, identify any problems with its current use and to canvass the
opinions of the operators as to its likely future applications. The results of this survey are given in
Section 6.
Manufacturers were approached individually and their responses used to complement the findings
of the survey.
In addition, a survey was undertaken of current and completed research in UK universities by
searching the 'BEST' CD-ROM database and seeking the views of the researchers involved. In
addition, various research establishments known to have an interest in materials research were
identified and contacted in a similar way.
In parallel with the above surveys an extensive literature search was undertaken, initially using the
on-line facilities of the Science Reference Information Service and the University of Surrey library
The current status of knowledge relevant to the use of titanium in offshore oil and gas production
has been established from this literature search, the survey of research establishments, and from
information from manufacturers.
The results of the above work have been assessed and consolidated to establish the research
needed on titanium alloys in relation to its use offshore.
2.3 Background
Titanium is available in many grades, most of them developed for the aerospace industry.
However it is widely and increasingly used in the offshore industry for heat exchangers and
seawater piping systems on topsides plant and ballast systems. As an indication of this, titanium
usage on large fixed platforms in Norway has grown to over 150 tonnes per platform.
Steel has traditionally been used for components of production systems such as rigid risers, tie-in
spools and manifold pipework. Environmental and reservoir conditions have prompted the
development of special steels such as super duplex stainless and other materials, for example
flexible pipe sections made of reinforced elastomers and/or polymers. Progress is also being made
in the development of composites, and of coatings for steel.
10 Titanium Alloys Offshore (MTD 96/100)
Titanium has long been recognised to have some desirable properties for many components:
compared with carbon steel it is strong, light (approximately 60% the density of steel), flexible
(approximately half the elastic modulus of steel) and inert to most reservoir fluids. It is also
highly resistant to corrosion in seawater.
Four factors have stimulated an interest in titanium by oil and gas companies:
the extension of exploration into very deep water
the discovery of high pressure, high temperature wells
the decline and stabilisation of the price of the metal
the possibility of wells becoming sour in the long term.
Titanium Alloys Offshore (MTD 96/100) 11
