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OTH88 283-

GROUTED AND MECHANICALSTRENGTHENING AND REPAIR OF

TUBULAR STEEL OFFSHORESTRUCTURES

Authors

R GHarwood&

EP ShuttleworthWimpey Offshore Engineers &Constructors Ltd27Hammersmith Grove

Hammersmith, London, W6 7EN

Preparedforpublicationby

Techword Services

153 LondonRoad

Hemel Hempstead, Herts, HP39SQ)

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This publication forms part of a series of reports to the Department

of Energy of work which has been wholly or in part supported byfunds provided by the Department. Neither the Department no r thecontractors concerned assume any liability Tor the reports nor dothey necessarily reflect the views or policy of the Department. Theprice of this publication has been set in order to make somecontribution to the preperation costs.

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FOREWORD

This report is the final outcome of the Joint Industry Repairs Research Project, carried out byWimpey Offshore Engineers and Constructors Limited with funding from the following organisations:

Amoco (UK) Exploration Company

BP International LimitedChevron Petroieum (UK) Limited

Conoco (UK) Limited

Hydrocarbons Great Britain Limited

Occidentai Petroleum (Caiedonia) Limited

Phillips Petroieum Company

Shell UK Exploration and Production

Societe Nationale Elf Aquitaine (Production)

UK Department of Energy.

The report is in five parts, corresponding to the five volumes of the original report:Designers' Manual - Part Iof this printed reportEngineering Assessment of Test Data - Part of this printed report except for the following,which are included as microfiches in the back cover of this report:- Tables and Figures of Section 11.4- Appendix II.7A- Appendix II.10A- Appendix II.A- Appendix II.6

Test Reports for Areas 1 to 5- included as microfiches in the back cover of this report

Test Reports for Areas 6 to 11-

included as microfiches in the back cover of this reportCrack Data- included as microfiches in the back cover of this report.

The original five reports were prepared with the guidance of a Technical Steering Committeecomprising:

Dr J V Sharp (Chairman) Marine Technology Support Unit

Mr N E Johnson (Secretary) Wimpey Offshore Engineers & Constructors Limited

Mr P E G O'Connor Amoco (UK) Exploration Company

Mr D G M Eggar BP International Limited

Mr V J Bromiey Chevron Petroleum (UK) Limited

Mr A Sen Gupta Conoco (UK) LimitedMr D Brown Hydrocarbon Great Britain Limited

Mr M B Green Occidental Petroleum (Caledonia) Limited

Mr R L Thomas Phiiiips Petroleum Company

Mr R Hemming Sheii UK Exploration and Production

Mr D Bergez Societe Nationale Elf Aquitaine (Production)

Dr I E Tebbett (Project Manager) Wimpey Offshore Engineers & Constructors Limited

Mr R G Harwood (Principal Wlmpey Offshore Engineers & Constructors Limited

Mr E P Shuttleworth authors) Wimpey Offshore Engineers & Constructors Limited.

Use has been made of data from earlier projects which have been kindly made available by thefollowing organisations:

Conoco (UK) Limited

Occidental Petroieum (Caledonia) Limited

Shell BP and Todd Oil Services Limited

Wimpey Offshore Engineers and Constructors Limited

UK Department of Energy.

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CONTENTS

SUMMARY

NOMENCLATURE

PART I DESIGNERS' MANUAL

1.1 INTRODUCTION

1.1. 1 General

1.1.2 The need for repair and strengthening

1.1.3 Use of the designers' manual

1.2 BACKGROUND TO THE DESIGNERS' MANUAL

1.2.1 General

1.2.2 Grouted connections

1.2.3 Grouted repairs

1.2.4 Mechanical and stressed grouted repairs

1.2.5 Grout-filled tubulars

1.2.6 Description of the Joint Industry Repairs Research Project

1.3 DESCRIPTION OF GROUTED AND MECHANICAL REPAIR SYSTEMS1.3.1 General

1.3.2 Terminology

1.4 GROUTED CONNECTIONS

1.4.1 lntroduction and definitions

1.4.2 Applications

1.4.3 Factors affecting the strength of grouted connections

1.4.4 General recommendations

1.4.5 Static strength of a grouted connection

1.4.6 Ranges of application and other requirements

1.4.7 Permissible working stress

1.4.8 Safety factors

1.4.9 Applied stresses

1.4.10 Fatigue

1.4.11 Movements during grouting

1.5 GROUTED CLAMPS


1.5.2 Applications1.5.3 Factors affecting strength

1.5.4 Fatigue



Page

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MECHANICAL CONNECTIONS


1.6.2 Applications

1.6.3 Factors affecting the strength of mechanical connections


1.6.5 Static coefficient of friction for mechanical connections

1.6.6 Ranges of applicability and other requirements

1.6.7 Permissible working loads


1.6.9 Applied loads

1.6.10 Fatigue

1.6.1 1 Studbolt load attenuation

MECHANICAL CLAMPS

1.7.1 lntroduction and definitions1.7.2 Applications

1.7.3 Factors affecting the strength of mechanical clamps

1.7.4 Fatigue



STRESSED GROUTED CONNECTIONS


1.8.2 Applications1.8.3 Factors affecting the strength of stressed grouted connections


1.8.5 Static strength of a stressed grouted connection

1.8.6 Ranges of application and other requirements

1.8.7 Permissible working loads


1.8.9 Applied loads

1.8.1 0 Fatigue

1.8.1 1 Studbolt load attenuation

STRESSED GROUTED CLAMPS


1.9.2 Applications

1.9.3 Factors affecting strength

1.9.4 Fatigue



1.10 GROUT FILLED TUBULAR MEMBERS1.10.1 lntroduction and definition

1.1 0.2 Applications

1.10.3 Factors affecting the strength of grout filled tubular members

1.1 0.4 General recommendations

1.10.5 Range of application

1.10.6 Determination of ultimate capacity of a grout filled tubular

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Permissible working loads and safety factors

Applied loads

Heat generation

1.11 GROUT MATERIALS AND GROUTING PROCEDURES FOR GROUTED REPAIRS1.11.1 Materials

1.1 1.2 Assessment of compliance of grout strength

1.1 1.3 Offshore oractices

1.12 BASIC INFORMATION ON TUBULAR JOINTS

1.12.1 Static strength

1.12.2 Stress concentration factors

1.13 ADDITIONAL DESIGN CONSIDERATIONS

1.1 3.1 Introduction1.13.2 Bolting systems

1.13.3 Sealing systems

1.13.4 Cathodic protection

1.13.5 Inspection

1.13.6 Additional loading

1.13.7 Wetwelding

REFERENCES-PART I

PART II ENGINEERING ASSESSMENT OF TEST DATA

I I .1 INTRODUCTION

.II.2 SUMMARY OF PREVIOUS WORK

II.2.1 General

I I . 2 . 2 Grouted connections

II.2.3 Grouted clamps

II.2.4 Mechanical connections and clamps

II.2.5 Stressed grouted connections and clamps

II.2.6 Grout filled tubulars

11.3 THE JOINT INDUSTRY REPAIRS RESEARCH PROJECT

DATASHEET 1. 1

DATASHEET 1.2

DATASHEET 1.3DATASHEET 1.4wb

DATASHEET 1.4st

DATASHEET 1.5DATASHEET 2

DATASHEET 3

DATASHEET 4

DATASHEET 5

DATASHEET 6

DATASHEET 7

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DATASHEET 8

DATASHEET 9

DATASHEET 10

DATASHEET 11

GROUTED CONNECTIONS

II.4.1 lntroduction

II.4.2 Factors affecting a grouted connection's strength and behaviour

II.4.3 Assessment of grouted connections data for repair

GROUTED CLAMPS

II.5.1 Definitions

II.5.2 Applications

II.5.3 Factors affecting strength

II.5.4 FatigueII.5.5 Applied stresses

II.5.6 Safety factors

MECHANICAL CONNECTIONS

II.6.1 lntroduction

II.6.2 Factor affecting a mechanical connection's strength and behaviour

II.6.3 Flat plate friction tests

II.6.4 Limits of application of generalised formula for mechanical connections


MECHANICAL CLAMPS

II.7.1 Definitions

II.7.2 Applications


II.7.4 Fatigue

II.7.5 Applied stresses


Appendix II.7.A Studbolt load losses due to top plate bending

STRESSEDGROUTEDCONNECTIONSII.8.1 lntroduction

II.8.2 Factors affecting the strength and behaviour of stressed grouted connections

II.8.3 Generalised equation for the static coefficient of friction for a stressedgrouted connection

II.8.4 Limits of application of the generalised formula for stressed grouted connections


STRESSED GROUTED CLAMPSII.9.1 Definitions

II.9.2 Applications


II.9.4 Fatigue

II.9.5 Applied stresses. .

II.9.6 Safety factors 224

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11.10 GROUT FILLED TUBULAR MEMBERS

11.10.1 Introduction

11.10.2 Factors affecting the strength of grout filled tubular members

11.10.3 Design curves

Appendix I I.10.A Example calculation

REFERENCES- PART II

APPENDIX I I.A INVESTIGATION INTO WELDING UNDERWATER

APPENDIX II.B FASTENER SYSTEMS

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SUMMARY

This document is the outcome of the Joint Industry Repairs Research Project (JIRRP), funded by theUK Department of Energy and nine oil companies. The research carried out investigated the staticstrength and fatigue performance of grouted and mechanical connections and clamps of the typesused to strengthen or repair underwater tubular steel members. The repairs may be needed as aresult of fatigue damage, increased code requirements, damage from ship impacts, etc.

Data from the research and from other sources has been assimilated and used in the compilation ofPart I of the document, the 'Designers' manual'. In general the factors addressed for each type ofunderwater repair include:

its applications

factors affecting its strength

general recommendations

static strengthranges of application

permissible working loads

safety factors

applied loads

* fatigue.

The concluding chapters of the manual describe grouting materials and procedures and otherrelevant considerations in the design of repairs, such as boiting and sealing systems, CP, inspection

and wet welding.

An experienced and competent engineer should find the manual of considerable benefit in designinga specific repair and justifying the design to the regulatory authorities. However, each repair is uniqueand the manual does not give standard solutions to standard problems.

Part II of the document is a more detailed 'Engineering assessment of test data' in which the factorsaffect ing the strength and behaviour of each type of clamp or connection are discussed in moredetail.

The microfiches at the back of the document contain the remaining three parts of the original JIRRPreport:

Part II I -Test reports from Areas 1-5

Part IV-

Test reports from Areas 6-

1 1Part V-Crack data.

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PART l

DESIGNERS' MANUAL

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I.1 INTRODUCTION

I.1 .1General

This manual is intended to provide designers with some basic information obtained from specific

laboratory tests concerning grouted and mechanical repair systems. The design formulae and otherinformation provided here and in the microfiches is the product of a comprehensive research project

on grouted and mechanical strengthening and repair systems carried out between 1982 and 1984 atWimpey Laboratories with funding from nine oil companies and the UK Department of Energy. Thedesign methods and formulae presented also draw on test work carried out prior to 1982 on an adhoc basis for oil companies and the UK Department of Energy.

The use of grouted and mechanical repair systems in both unde rwater and splash-zone applicationshas increased dramaticallyin recent years. This has been due to the increased number of repairsbeing effected as designers and operators recognise the cost effectiveness of grouted andmechanical repairs and the availibility of test data describing their performance. This document

represents a major step forward in the assimilation of test data into a format which can readily beused in both the design of a repair and in the justification of the design to regulatory authorities.

It should be noted that all repairs are unique. This is because of the wide range of reasons for repairand strengthening,the many different structural configurations, member sizes and joint details, andthe physical constraints of access to different water depths and different parts of the structure. Forthis reason this designers' manual cannot give a standard solution for a particular problem. It isrecommended that the designer of a repair or strengthening systems should be familiarised withrecent projects and techniques before making judgements on the efficacy of particular systems.

Although there is no standard repair scheme, it is possible to recognise the following componentswithin the various grouted and mechanical repair schemes that have already been employed and are

defined below:

GROUTED CONNECTIONA connection between two concentric tubulars formed by the injection of a cemetitious materialinto the annulur space between the tubulars. Unless specifically stated the outer tubular istaken to be continuous in the circumferential direction.

- GROUTED CLAMPA clamp in which the outer sleeve is formed in two or more segments which are placed aroundan existing tubular joint. The splits are closed by pre-tightened bolts prior to the injection of acementitious material into the annulur space between the clamp and the existing tubular joints.

MECHANICAL CONNECTIONA connection formed between two concentric tubulars relying for load transfer on the frictioncapacity of the interface between the two tubulars. The outer tubular will be formed from two ormore segments which are stressed together to generate a force normal to the friction surface.

MECHANICAL CLAMPA clamp in which the outer sleeve is formed in two or more segments which are placed aroundan existing tubular joint. The clamp body will be formed from two or more segments which are

stressed together to provide the load path in the clamp.

STRESSED GROUTED CONNECTIONA connection formed between two concentric tubulars. The outer tubular is formed in two or

more segments. Cementitious material is placed into the annular space between the tubularsand allowed to reach a predefined strength prior to the application of an external stressingforce normal to the steel-grout interface.

STRESSED GROUTED CLAMPA clamp in which the outer sleeve is formed in two or more segments which are placed aroundan existing tubular joint. Cementitious material is placed into the annular space between the

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clamp and the existing tubular joint and allowed to reach a predefined strength prior to theapplication of an external stressing force normal to the steel-grout interface.

* GROUT FILLED TUBULARA tubular which has been filled with a cementitious material

A clamp is distinct from a connection in that it is used to repair or strengthen a tubular joint within anexisting structure by providing an alternative parallel load path, whilst a connection is a device forjoining concentric tubular members together.

The design of a clamp will involve the following:

1. design of the connections which transmit a proportion of the load in the incoming bracemembers into the clamp

2. design of the joints to transmit the loads between the brace and chord members of the clampand existing joint

3. design of the connections which retransmit the clamp loading back into the chord member of

the existing joint.

For an illustration of these distinctions see Figure I.1 .l

All the above design components have been studied within the Joint lndustry Repairs ResearchProject and are addressed within individual sections of this manual.

This part is one of five volumes which represent the final report of the Joint lndustry RepairsResearch Project. The full list of volumes is:

Volume I - Designers' manual (printed here as Part I)

Volume II - Engineering assessment of test data (printed here as Part II)

8 Volume Ill-

Test reports for Areas 1 to 5 (see microfiches)0 Volume IV - Test reports for Areas 6 to 11(see microfiches)e Volume V - Crack depth measurement and propogation data (Areas 7 to 9) (see

microfiches).

1.1.2 The need for repair and strengthening

This section identifies the major causes leading to a requirement for repair and strengthening of

tubular steel offshore structures and draws on experience gained in the North Sea and other similarlyharsh environments on a world-wide basis.

Fatigue

The design of the early jackets in the North Sea was heavily dependent on experience in the Gulf ofMexico and elsewhere. In general these designs have been found unable to withstand the incessant

wave loadings of the North Sea and most structures, or some component of them, have requiredfatigue damage to be repaired, or have needed to be strengthened to prevent anticipated damage.Fatigue damage typically takes the form of cracks at the end of horizontal members where theyframe into the main structure.

Increased code requirements

Since the 1960s, following the assimilation of fresh environmental data, the wave loads whichregulations require offshore installations to withstand have increased - dramatically in somerespects. On occasion it has been found necessary to upgrade the structural performance of jacketsto meet the new requirements, or to meet other requirements subsequently introduced by the ownersof the jacket.

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Ship impacts

Damage is also caused by shipping. Personnel transfer in the North Sea is now almost exclusively byhelicopter. Regular transfer by boat has proved impossible because of the sea states in the NorthSea and much damage was caused by ship impact before platform operators started to usehelicopters. Ship impacts still occur as vessels are used to transport equipment and supplies, but thevessels can stand further off the platforms whilst the goods are taken aboard by cranes. Damagecaused by ship impacts typically takes the form of bent or buckled members, although on occasionentire members have been ripped out.

impactbydebris

Objects are sometimes dropped overboard causing damage to the jacket on their way to the sea -bed. The most serious damage has been caused during the installation of jackets or during othererection work. An entire bridge intended to link two platforms has been dropped, and heavy offshorepiles have been lost on more than one occasion.

The reader is referred to Reference 1 .l for a more detailed review of repairs that have been carriedout on North Sea structures.

1.1.3 Use of the designers' manual

The design methods and formulae given here and later in this report provide the designer with themeans to design the individual components of some repair schemes such as clamps or connections.It is not intended that this document should provide the designer with guidance on the form of specificrepair schemes since each repair problem is unique. The choice of whether to clamp an under-strength joint locally or to introduce extra members into the structure, thereby changing the load patharound the understrength joint, is one that should be made with full knowledge of the platform

geometry and loading regime and should be such as to give maximum benefit to the structure as awhole. It is at this early stage that proper consideration should be given to the extra loads that will beattracted by the repair scheme; these loads would be used at a later stage in the design of theindividuai components.

Extra loads which should be considered would typically include:

1. environmental loads due to increased projected area and weight of components for waveimpingement and higher drag coefficients due to non tubular fabrication

2. framing loads due to changes in load paths and increased local stiffness due to clamps.

Within the individual sections of this manual giving the design methods and formulae, ranges ofapplication are given which reflect the geometries tested and the designer should not exceed theselimits except where guidance is given in the text on how this may be achieved without loss ofconservatism.

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LOADS

2.JOINT IN

Figure 1.1.1

BRACE MEMBER

UBULAR JOINT

BRACE CONNECTION

,- CLAMP

\--- ~ ~~Distinction between clamps and connections

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1.2 BACKGROUND TO THE SIGNERS' MANUAL

I.2.1 General

This designers' manual has been made possible by:

the recognition that grouted and mechanical repairs can offer major advantages in cost andtimescale

* the existence of rationaliy based design formulae for axially loaded grouted connectionssupported by test data

* the generation of a basic database under UKDepartment of Energy funding on grouted repairs

* the availability of the results of some ad hoc testing programmes carried out to justify thedesign of some repairs installed before the existence of this manual

* the data collected under the Joint Industry Repairs Research Project

* experience gained by the autliors in the design and execution of actuai repairs, many of which

have been undertaken in parallel with all the development work leading to this manual.

1.2.2 Grouted connections

The majority of steel offshore structures are founded on tubular piles, which are generally driventhrough tubular sleeves attached to the lower part oi the main legs of the structure or through themain legs. The annulus between pile and sieeve is then filled with cement grout to form thepermanent connection between the structure and its foundation, The strength of this connection

depends upon many parameters and is generally defined in terms of an equivaien! bond strength(obtained by dividing the load transmitted by the nominal surface area of the groutipile interface).

The current design method is based primarily on static strength considerations and uses formulaederived from test data. Data are now available on the fatigue performance of grouted connectionsand it is therefore now possible to address fatigue design.

The first design guidance provided for grouted connections was given by early editions of API RP2A.A single figure of permissible bond stress was given for plain pipe grouted connections which wasbased on rest data from reiativeiy small diameter specimens. The development of a capability toinstall larger piles to meet the demand of larger structures in the North Sea led in the early 1970's toan investigation of the static strength of large diameter grouted connections. This showed that plainpipe connections of the type and length envisaged could not provide sufficient load transfer capacity;shear connectors in the form of circumferential or spiral weld beads were placed on the steelsurfaces in contact with the grout to provide additional capacity and tests were carried out to validate

the design.

Further ad hoc tests were carried out between 1975 and 1978 for oil companies wishing to solveparticular design problems. Whiist these tests were usefui in establishing the parameters which affectstatic strength, the accumulated data did not cover all aspects of the problem and the results could

not be used to formulate rationally based design recommendations giving consistent levels of safety.A detailed programme of research was therefore formulated and undertaken with funding from theUK Department of Energy.

The UK Department of Energy project consisted of five phases:

Phase l Static strength tests

Phase II Early age cyclic loading testsPhase Il l Long term fatigue tests

Phase IV Measurement of grout compressive strengths

Phase V Tests on connections recovered from West Sole.

Much of the information used to generate the design formulae given in this manual has been derivedfrom this important project and the results and findings of the work are taken into account in Part 2.

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