The application process of fusionbonded epoxy as field joint coating - Het applicatie proces van fusion-bonded epoxy als field joint coating

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The application process of fusion-bonded epoxy

as field joint coating

Geert Jan Kap

Faculty of Mechanical, Maritime and Materials Engineering Faculty of Civil Engineering and Geosciences

Faculty of Technology, Policy and Management Delft University of Technology

Allseas Engineering BV

Thesis

Master of Science - Transport, Infrastructure and Logistics August 2013

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Preface

This report marks the final steps towards my graduation. It describes my thesis work, which I completed at Allseas Engineering BV in corporation with Delft Technical University. During this masters thesis I enjoyed the combination of scientific knowledge with hands on experimenting. One day I would be reading about the chemical cross linking of thermosetting polymers. The next day I would build a machine and clean the excess epoxy powder out of a fluidised bed with a shop vac. To me this is the definition of being a true engineer.

A wise man once said: when thanking people you should mention everybody or nobody at all. True words, but with the risk of forgetting a couple I will give it a try. First off I would like to thank my graduation committee for their support, comments and guidance throughout the process. Professor Rijsenbrij for his enthu-siasm on the subject. Wouter van den Bos for helping me stay on topic. Professor Heijnen for her help with getting my thoughts on paper. Kirill and Erik, for their vast knowledge and discussions on the topic of field joint coating. Manuel, Jos, Mark, Warner and everybody else from PPD and the yard in IJmuiden for their support during the tests. My roommates in C3.27 and the colleagues I shared a pool-car with or shared a small break with by the coffee machine. My parents Aaldrik and Marianne, my family and my parents-in-law Wolter and Arina for their never ending support. My close friends for the good times we had besides our studies and Arne in particular for his tips on writing the final report.

I would like to thank Allseas for the chance they gave me to do my thesis work at their exciting company. I am grateful for the chances given and I am looking forward to continue my career within the company.

Finally I would like to thank my lovely girlfriend Fenna for sticking by my side for all these years and especially these final weeks. Your love and support were of great significance for the completion of this thesis and the successful ending of my career as a student.

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Delft University of Technology

FACULTY MECHANICAL, MARITIME AND MATERIALS ENGINEERING

Department Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

This report consists of 99 pages. It may only be reproduced literally and as a whole. For commercial purposes only with written authorization of Delft University of Technology. Requests for consult are only taken into consideration under the condition that the applicant denies all legal rights on liabilities concerning the contents of the advice.

Specialization: Transport Infrastructure and Logistics Report number: 2013.TIL.7786

Title: The application process of

fusion-bonded epoxy as field joint coating

Author: G.J. Kap

Title (in Dutch) Het applicatie proces van fusion-bonded epoxy als field joint coating

Assignment: Master thesis Confidential: yes

Initiator (university): Prof. ir. J.C. Rijsenbrij (Delft University of Technology) Initiator (company): Dr. K. Kavelin, Ir. E. Kramer (Allseas Engineering BV, Delft) Supervisor: ir. W. van den Bos, Dr.ir. P.W. Heijnen

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Student: G.J. Kap Assignment type: Master thesis Supervisor (TUD): ir. W. van den Bos, Dr.ir.

P.W. Heijnen (TU Delft)

Creditpoints (EC): 30 Supervisor (Company) Dr. K. Kavelin, Ir. E.

Kramer (Allseas Engineering BV)

Specialization: TIL

Report number: 2013.TIL.7786 Confidential: Yes

Subject: The application process of fusion-bonded epoxy as field joint coating

Allseas is one of the leading offshore pipeline installation contractors in the business. For the installation of pipes, it uses the so called S-lay method, a method where pipe sections, called joints, are assembled into a continuous pipeline at the firing line, on-board the pipe lay vessel. Subsequent stations perform welding, non-destructive testing and coating tasks in this firing line. Since the founding of the company in 1985, much of the equipment to perform these tasks was designed, developed and built in-house. A lot of effort was put into improving installation time. Allseas and its clients mainly focused on the welding and NDT testing stations while the coating process drew relatively less attention.

In recent years the attention of the clients of Allseas shifted to the coating stations. There were also signals that on some projects the process time of individual coating stations negatively affected the overall installation time. This has triggered Allseas to also improve the coating process, with a focus on process times, while coating quality should not suffer. A combined machine for heating and coating was used, a mechanical blaster was installed in the firing line and the grit blast equipment was scaled up with the addition of more blast heads. Some of these improvements were more successful than others.

The assignment of this master’s thesis is to make an analysis of the current coating process and find possible improvements. These improvements should be tested on process times and coating quality. Finally an advice should be given about the implementation of these improvements within the current pipeline installation process.

The report should comply with the guidelines of the section. Details can be found on the website. The professor,

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Summary

Allseas is one of the leading offshore pipeline installation contractors in the busi-ness. For the installation of pipes, it uses the so called S-lay method, a method where pipe sections are assembled into a continuous pipeline at the firing line, on-board the pipe lay vessel. Subsequent stations perform welding, non-destructive testing and coating tasks in this firing line.

Since the founding of the company in 1985, much of the equipment to perform these tasks was designed, developed and built in-house. A lot of effort was put into improving installation time. Allseas and its clients were mainly focused on the welding and NDT testing stations while the coating process drew relatively less attention.

In recent years the attention is shifted to the coating stations. There were also sig-nals that on some projects the process time of individual coating stations negatively affected the overall installation time.

Although some effort was made in the past to improve the coating process the re-sults were disappointing. The need for reducing overall process times while main-taining coating quality still remains. Therefore Allseas initiated this research, exploring possible changes to the coating process.

A preliminary research showed that fusion-bonded epoxy is the most used coating type. Based on that the choice was made to focus the research on the application process of fusion bonded epoxy.

The goal of the research was formulated as a research question: What are the possibilities to change the current process of field joint coating application, in order to achieve faster cycle times while maintaining the current coating quality, while taking into account requirements for changes to the process?

To answer the research question the current process of pipeline production was analysed. From this analysis it was concluded that there were three possibilities for changes to the process:

• The order of steps within the process • Combination of steps within the process • Alternative methods within the process step

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joint coating stations could be critical. From the limited amount of data available it could be seen that the most time was used at the station where the joint is heated and coated. Analysis of cycle times did not show the surface preparation station to be critical. Interviews with Allseas employees however confirmed that for some projects the surface preparation station was critical.

The analysis of the current equipment used for the application process of fusion-bonded epoxy was done. This research showed that the current method of surface preparation, grit blasting, could be improved. The current method gives good results, but due to a limitation in space for the grit handling units it is difficult to optimise this method.

The method of heating the joint with induction heating is the most efficient and clean way. The shape of the coil however could be changed in order to combine the heating coil with other equipment.

A research into possible alternatives was done, based on the conclusions of the analysis of the current process and equipment. A number of possible alternatives were found.

The order of steps within the process:

• Pre-blasting with mechanical blasting followed by cleaning with laser or dry ice

• Pre-blasting with grit blasting followed by cleaning with laser or dry ice Combination of steps within the process:

• Shockwave Induced Spray Painting

• Combined Heat & Coat machine with alternative heating coil Alternative methods within the process step:

• Dry ice with grit blasting instead of grit blasting • Pick brush instead of grit blasting

• Low application temperature FBE instead of FBE

• Surface treatment with laser blasting instead of grit blasting

Based on found requirements for new equipment and the change of the process, a number of these alternatives were chosen to further research:

• Pre-blasting with mechanical blasting followed by cleaning with laser or dry ice

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• Low application temperature FBE instead of FBE

• Surface treatment with laser blasting instead of grit blasting

Practical tests were performed to see whether these possible alternatives could lead to the reduction of cycle times while maintaining the coating quality. A test setup was designed and built in-house. The test setup replicated the process in the firing line. Steel plates were used, which were treated with the different surface treatment methods. After that they were heated in an industrial oven. After heating they were coated with FBE. Once the FBE was fully cured, destructive tests were performed to evaluate the level of the quality of the coating.

During the tests different measurements were taken. The time each of the surface treatment methods took was recorded. The noise levels of the surface treatment were recorded as part of the safety aspect. During the destructive test the degra-dation of the coating was measured.

Based on the test result it was concluded that there are three alternatives that can be identified as prominent alternatives for FBE application:

• Pre-blasting with mechanical blasting followed by cleaning with laser • Dry ice with grit blasting

• The application of LAT FBE

Based on the conclusions some further recommendations can be made for each of the three possible alternatives.

Pre-blasting with mechanical blasting followed by cleaning with laser:

• Research the possibilities for the incorporation of a mechanical blaster in the bevelling station

• Further test the use of laser equipment in the current process and with the current equipment

• Investigate possible safety issues related to the use of laser equipment Dry ice with grit blasting:

• Research the logistics of dry ice pellets

• Research the possibility of producing of dry ice on board the vessels • Execute more tests with different types of blast media added to the dry ice • Research the possibilities for the reduction of noise levels

• Investigate the possible safety issues with CO2 The application of LAT FBE:

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equipment

• Research the cost aspect of applying LAT FBE powder with respect to the reduction of time (cost versus gain)

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List of Figures

1.1 S-lay method . . . 3

1.2 Firing line on board PLV Solitaire . . . 4

1.3 Schematic overview of the firing line of the Solitaire . . . 5

1.4 Percentage of field joints per surface preparation method . . . 7

1.5 Percentage of field joints per coating type . . . 8

2.1 Scematic overview of the process . . . 15

2.2 Process of pre-production . . . 16

2.3 Example of a J-bevel and a K-bevel . . . 17

2.4 Process of welding . . . 17

2.5 Build-up of welds in the pipeline wall . . . 18

2.6 Schematic process overview of Field Joint Coating . . . 20

2.7 Typical field joint . . . 20

3.1 Anchor profiles on substrate; left is shallow, right is deep[1] . . . 25

3.2 Sample of blast media: steel shot and grit mix . . . 26

3.3 Grit blast frame in operation on the pipe . . . 27

3.4 Grit handling unit - LTC . . . 28

3.5 Green mile of PLV Solitaire . . . 29

3.6 Heating coil . . . 30

3.7 Heat profile along the field joint[2] . . . 31

3.8 FBE coating frame . . . 32

3.9 Inside of the coating ring of the application frame . . . 32

3.10 Fluidised bed together with control panel . . . 33

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4.2 FBE application dishes . . . 37

4.3 Combined steps process for heat and coat machine . . . 38

4.4 Contact blocks of heat and coat machine . . . 38

4.5 Spacing between the heating coil and pipe . . . 39

4.6 Mechanical blasting machine [3] . . . 40

4.7 Bauhaus mechanical blaster in FL . . . 41

4.8 Surface preparation with laser beam . . . 42

4.9 Laser treatment of steel piece . . . 42

4.10 Pellets of dry ice used for blasting . . . 43

4.11 Principle of dry ice blasting [4] . . . 44

4.12 Power wire brush with hardend bent ends [5] . . . 44

4.13 Power wire brush frame . . . 45

4.14 Schematic overview SISP process [6] . . . 46

5.1 Test plates blasted and put outside . . . 51

5.2 Corroded test plates . . . 51

5.3 Test setup . . . 52

5.4 Grit blast head fitted in test setup . . . 53

5.5 Test plates in industrial oven . . . 54

5.6 FBE application nozzle fitted in test setup . . . 54

5.7 Mechanical blaster test setup . . . 55

5.8 Simulating FL conditions with heat and NDT water . . . 56

5.9 Dry ice blasting method . . . 57

5.10 Laser treatment test setup . . . 57

5.11 Surface comparator with mechanical blasted test plate . . . 60

5.12 Measuring of the Testex tape . . . 61

5.13 Surface after mechanical blasting . . . 62

5.14 Surface after laser blasting . . . 62

5.15 Test setup Noise level measurement . . . 63

5.16 Cured coating on a test plate . . . 64

5.17 Adhesion test - resistance to removal . . . 65

5.18 Pull-off tester and 20mm dollies glued to test plate . . . 66

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LIST OF FIGURES 5.20 Cathodic disbondment test setup at Element, Amsterdam . . . 69 5.21 Cathodic disbondment on test plate . . . 70

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List of Tables

2.1 Firing line stations overview . . . 15

2.2 Joint types . . . 16

2.3 Cycle times of the three main steps . . . 21

2.4 Cycle times per station . . . 21

5.1 Anchor profile measurements . . . 61

5.2 Cycle time measurements . . . 63

5.3 Noise level measurements . . . 63

5.4 Dry film thickness measurements . . . 64

5.5 20mm dolly pull-off test measurements . . . 67

5.6 14mm dolly pull-off test measurements . . . 67

5.7 Cathodic disbondment test results . . . 70

5.8 Test results summarised . . . 71

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Glossary

DJF Double Joint Factory FBE Fusion-bonded Epoxy FJ Field Joint

FJC Field Joint Coating FL Firing Line

HSS Heat Shrink Sleeve LE Liquid Epoxy

NDT Non-Destructive Testing OD Outside Diameter PLV Pipelay Vessel PP Pipeline Production

PPD Pipeline Production Departement PQT Procedure Qualification Trial PWB Power Wire Brush

QHSE Quality, Health, Safety and Environment WT Wall Thickness

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1

Introduction

This chapter introduces the topic of this masters thesis. Section 1.1 will give a general introduction of the topic. In section 1.2 the problem definition is stated. In section 1.3 the relevance of the research is stated. In section 1.4 the goal of the research is sketched. Finally in section 1.5 the structure of the report is given.

1.1 General introduction

Around the world many offshore platforms extract hydrocarbons in the form of oil and natural gas. One way to transport these hydrocarbons between platforms wells and onshore is by means of pipelines. This method of transportation is a low cost alternative with respect to tons per kilometre. Before transportation can commence the pipeline needs to be produced and installed.

Allseas is a company that installs those pipelines. As a commercial company their goal is to lay the best pipeline possible in the shortest amount of time. To be able to do this, they have to constantly monitor and improve their method of pipeline installation and production. With this in mind Allseas has been the originator of this research. Before the research is further explained an introduction to Allseas and the installation and production of pipelines is given.

1.1.1 Allseas

The Swiss-based Allseas Group S.A. is a global leader in offshore pipeline installation and subsea construction. The company employs over 2,000 people worldwide and

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oper-ates a versatile fleet of specialized pipelay and support vessels, designed and developed in-house [7].

The basis of this fleet, are the pipelay vessels (PLVs): • Solitaire (300 m)

• Audacia (225 m) • Lorelay (182.5 m) • Tog Mor (111 m)

All vessels are capable of handling pipelines with outside diameters (OD) ranging from 2 inch to 60 inch, except for PLV Lorelay, which is limited to a maximum OD of 28 inch. PLV Solitaire has achieved pipelay speeds in excess of 9 km/day [7].

Currently Allseas is building her fifth PLV, the Pieter Schelte. She will be commis-sioned in 2014. The Pieter Schelte will then be the biggest PLV in the world with an overall length of 382 meter. She will be capable of laying pipelines up to a maximum OD of 68 inch.

The philosophy within Allseas has always been to develop and design its own equip-ment, ranging from the Phoenix welding system up to the biggest pipelay vessel thus far, the Pieter Schelte. From this philosophy the department of Innovations has tried and tested numerous different methods of pipeline production and continues to perfect and adapt its equipment. The main reason to apply this philosophy is to stay ahead of the competition and to be independent from (sub) contractors. Allseas uses a specific method of pipeline installation which is explained in the next section.

1.1.2 Pipeline installation

There are a number of different methods for the offshore installation of pipelines. The choice for each one of these methods relies on a number of factors. The most important being water depth and the OD of the pipe. For Allseas two methods are suited. The first method is the so called S-lay method. The second is the so called J-lay method [8]. The letters S and J, describe the shape of the pipeline from the PLV to the ocean floor.

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1.1 General introduction With the J-lay method the pipeline is produced in a vertical tower. At the deck level al the steps to produce the pipeline are performed in the same station. S-lay describes the method of pipeline installation where the pipeline is produced horizontally.

The main advantage of S-lay is the fact that it is possible to simultaneously conduct several steps needed for pipeline production. These are done in multiple stations along the length of the ship. There are different stations for welding, non-destructive testing (NDT) and field joint coating (FJC).

The pipeline follows the shape of the letter S, from the vessel to the bottom of the sea as seen in figure 1.1. To support the pipeline while leaving the vessel a stinger is attached. The stinger is a support structure that limits the bend radius of the pipeline and prevents buckling of the pipeline.

Figure 1.1: S-lay method

Several tensioners fitted with tracks hold the pipeline in the vessel. The tensioners are controlled to move the pipeline in and out of the vessel. This is done automatically to compensate for vessel motions due to waves. The deeper the pipeline needs to be installed the higher tension is needed to hold the pipeline with the tensioners.

Allseas has designed and developed systems for J-lay and S-lay installation. The choice was made for the S-lay method because this method provides fast installation for all pipeline ODs over a large range of water depths in comparison with the J-lay method [8]. The choice for the S-lay method resulted in a specific layout of the pipeline production, which is described in the next section.

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1.1.3 Pipeline production

The production process of a pipeline can be compared to a standard production process in a factory. A piece of pipe, called a joint, enters the factory. During the production process joints are connected to form a continuous pipeline. The factory is the firing line (FL). Production rates can be increased with the addition of a double joint factory (DJF) to the FL. In the DJF two single joints are connected to form a double joint before entering the FL.

Firing line

In each of the four PLV’s of Allseas the joints are transformed in a continuous pipeline in the firing line. The FL is situated along the length of the vessel. It is divided in a number of work stations. There are a number of consecutive stations where the welding of the joints takes place. In figure 1.2 the firing line of PLV Solitaire is presented.

Figure 1.2: Firing line on board PLV Solitaire

When two joints are welded together both cut-back sections together are called a field joint (FJ). A cut-back is the bare section on both ends of the joint. In the next station the weld is checked with ultrasonic sound, this station is called the NDT station.

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1.1 General introduction Finally there are a number of stations that together perform the task of coating the FJ.

During each production cycle each station performs its individual task. When the task is completed the operator gives a signal. Once all stations have signalled they are ready, the pipeline can move to the next station. The distance that the pipeline moves between stations is called a pull. The vessel moves forward in the lay direction and the tensioner pays out the length of one pull. Each FJ then arrives at the next station, while the last FJ moves to the stinger.

In figure 1.3 a schematic overview of the FL of the Solitaire is presented. On the bow of the vessel the FL starts with the welding stations. At the stern of the vessel, the stinger is situated.

Figure 1.3: Schematic overview of the firing line of the Solitaire

Double joint factory

In order to increase lay rates the Solitaire is equipped with a Double Joint Factory (DJF). In the DJF single joints are welded together to form a double joint. The firing line of the Solitaire is therefore twice as long as that of the other vessels. The newly build Pieter Schelte will also be equipped with a double joint factory. In the DJF joints are welded and the weld is inspected with NDT. Coating of the welded double joint does not take place in the DJF. Coating takes place in the FL where more FJC stations are available.

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1.2 Problem definition

During the pipeline production process it is important to minimize the time that each joint has to be in a single station (cycle time), whether it is one of the welding stations, NDT or FJC stations. Furthermore it is important to synchronise the cycle times of the stations with each other. This results in an optimal usage of the production potential. The reduction in cycle times lead to lower overall production process times and minimizes project costs.

To achieve this, a lot of attention over the past years was given to the welding and NDT process. Welding over the years has become more reliable with the introduction of the automated Phoenix welding system and cycle times have thus been reduced and became more constant. With the automation of non-destructive testing and welding the chances on defects and repairs have also been greatly reduced [9].

There is a tendency now to pay more attention to FJC. During recent projects it has been observed that cycle times of FJC stations were not coherent with welding and NDT. One of the approaches from Allseas was to build the combined heat and coat machine. The machine was capable of performing two steps in one. The machine however was bulky and not optimised, which resulted in a bad coating quality. Another step was the introduction of a wheelabrator (mechanical grit blast machine) in the FL. The principle was promising but the fixed nature of the machine was not ideal for use in the FL.

Although an effort was made in the past to improve the coating process the results were disappointing. The need for reducing overall process times while maintaining coating quality however remains. Therefore Allseas initiated this research, exploring possible changes to the coating process.

1.3 Relevance of the research

The coating process within Allseas has a number of variables depending on the project. For each project the FJ has to be coated to protect it against corrosion. This first layer of coating is called the anti-corrosion coating and is always applied to the FJ. Optionally a second coating can be applied to protect the pipeline against mechanical damage or to insulate the pipeline.

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1.3 Relevance of the research For each project the client in cooperation with Allseas decides on the type of anti-corrosion coating that will be applied. The choice for the type of coating also decides the type of surface preparation that must be done. Three types of anti-corrosion coat-ing can be distcoat-inguished: liquid epoxy (LE), fusion-bonded epoxy (FBE) and a heat shrink sleeve (HSS). Two types of surface preparation can be distinguished: power wire brushing (PWB) and air pressured grit blasting. When FBE is chosen, this automat-ically means that grit blasting is used for surface preparation. For LE and HSS both types of surface preparation can be chosen.

A preliminary research in to the choice for each of these types was done to establish the relevance of the research. With the results from this preliminary research a scope can be defined for the actual research.

1.3.1 Field joint coating project data

Analysis of available project data gives an indication of the relevance of the research of FJC application. The analysis is based on track records Allseas has of past projects and the known characteristics of planned projects. Due to missing data in this track record the overview is based on data from 2008 up until 2014. The overview is based on the number of FJs made in each of the pipeline installation projects for al PLVs combined.

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In figure 1.4 it can be seen that PWB was used for a great part in past. This has changed however. The use of grit blasting has risen. This can be explained by the rise in use of FBE as a FJC, which requires grit blasting. This can be seen in figure 1.5. In that figure it can also be seen that the use of HSS has diminished. LE is still used, but for limited amount of projects.

Figure 1.5: Percentage of field joints per coating type

From interviews with coating engineers from Allseas it became clear that in the future the use of HSS and LE will further diminish. The demand from clients of Allseas will mainly be FBE. As a result grit blasting will be the predominant choice for surface preparation.

1.3.2 Scope of research

Based on section 1.3.1 it can be concluded that FBE will be the most used field joint coating for the coming years within Allseas. The scope of this research will therefore lie on the application process of FBE. Another reason for this scope is the practical implementation. If changes to the process can be found which reduce the overall process times it will be possible for Allseas to benefit from these changes on a short term. Completely new forms of coating could possibly require more time to fully research and implement and are therefore out of the scope of this research.

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1.4 Goal of research Because the FBE coating application process only takes place in the FL, the DJF on Solitaire lies outside of the scope. The scope of the research will be on the FL itself. The application process of secondary coatings lies outside of the scope because the choice for secondary coatings is not as regularly as the application of anti-corrosion coating.

1.4 Goal of research

With the scope of the research defined in section 1.3.2 and the problem definition from section 1.2 the goal of the research can be set. This is done by first formulating the main research question, after which the approach of the research can be defined.

1.4.1 Research question

The main research question is formulated as follows: ’What are the possibilities to change the current process of field joint coating application, in order to achieve faster cycle times while maintaining the current coating quality, while taking into account requirements for changes to the process?’

To answer the main research question there are a number of sub-questions to be answered. These questions are:

I What is the current process of FJC application? II What equipment is used in the current process?

III What are the cycle times within the whole process of pipeline production? IV What defines the level of quality of field joint coating?

V What changes could be made to the current process? VI What are the requirements for changes to the process?

VII What alternatives are available for the process and the equipment? VIII Which of these alternatives can lead to faster cycle times?

IX Can these alternatives maintain the current quality level of field joint coating? X How can alternatives be implemented in the current process of pipeline installation?

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1.4.2 Approach

To answer each of the sub questions a certain approach is necessary. The approach for each of the question will be as follows:

I Analyse the current FBE application process through in-house literature and inter-views with Allseas employees to find possibilities for changes.

II Analyse the current FBE application equipment through in-house literature, inter-views with Allseas employees and a visual inspection of the equipment at the storage facility to find possibilities for changes.

III Analyse the project data that is available within the Pipeline Production depart-ment to get cycle times for different projects and to find which possibilities for change would have to most effect on overall cycle times.

IV Study publications and in-house literature on the topic of coating to find the pa-rameters which define the level of quality of coating and the methods to asses this level.

V List the possibilities for changes based on the findings of I, II and III.

VI Study publications and in-house literature and interview employees to find the requirements for changes to the process.

VII Find alternatives for the possibilities for changes as found in V through a literature study, interviews with Allseas employees and interviews with suppliers of coating equipment.

VIII Measure the cycle times of alternatives found in VII trough practical tests and project these times on the real-time process.

IX Measure the quality of the coating that has been made through practical tests based on the findings of IV.

X Give an advise on the implementation of the alternatives based on the findings of VI, VIII and IX.

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1.5 Structure of the report

The structure for the report will be as follows; In chapter 2 an analysis of the pipeline production process is given. In chapter 3 an analysis of the equipment used within the FJC process is given. In chapter 4 alternative application methods for the FJC process are researched. Based on found requirements the most promising ones are chosen. In chapter 5 the chosen alternatives are tested. Finally in chapter 6 the results of the tests are discussed and conclusions are drawn.

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2

Analysis - process

In this chapter an analysis will be made of the current process of pipeline production and the application of FBE as a field joint coating in particular. The whole process is analysed to give an indication of the role of the FJC process in the whole pipeline pro-duction process. The analysis should point out which possibilities there are to change the process of pipeline production. The analysis starts with stating the requirements for the pipeline production process in section 2.1. The process is described in sec-tion 2.2. In secsec-tion 2.3 an indicasec-tion of the cycle times of the stasec-tions is given. Finally in section 2.4 conclusions are drawn with respect to possibilities for changes of the process.

2.1 Requirements for the pipeline production process

To get an insight in the pipeline production (PP) process the requirements for the process are researched in this section. Requirements for the PP process in a certain project can be given from one actor to another actor. They can also be discussed and agreed upon by multiple actors. Four different actors can be distinguished in this process:

1. Allseas 2. Clients 3. Suppliers

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Clients are oil and gas companies who contract Allseas to install pipelines. Suppliers are companies who supply Allseas with equipment and / or consumables. Equipment can range from components to whole machines. Consumables can be grit for the grit blaster or FBE powder used in the coating machine. Independent parties can be gov-ernments or organisations like ISO, DNV or Lloyds. They standardise and formalise the requirements for pipeline construction and installation.

Requirements for a project are driven by the client and determined in detail in corporation with Allseas. These requirements can be categorized in three themes;

Time For Allseas to be competitive and be successful as a commercial company the main goal for the process of PP is to make as much pulls as possible in a given amount of time. To achieve this goal the cycle time of each of the individual work stations needs to be as low as possible. Next to that the cycle times per station need to be as close together as possible to use the production capacity to a maximum. The station that uses to most time to perform its individual task is called critical. The time needed for this station is the governing time for the total process time and the amount of pipeline that can be installed per day.

Quality The process needs to result in a pipeline that adheres to the agreed level of quality. This means that the process is designed in a certain way. Surface preparation for instance needs to take place before coating can be applied. It may be possible to make changes to the process while still adhering to the level of quality.

Safety and Health Within Allseas there is a Quality, Health, Safety and Environ-ment (QHSE) departEnviron-ment. This QHSE departEnviron-ment has the specific task of monitoring all the processes that take place within Allseas. One of their main tasks is the safety and wellbeing of employees. The PP process therefore needs to be designed in such a way that the safety and wellbeing of employees is guaranteed. Where possible, safety measures should be incorporated in the process.

2.2 Process description

In this section the complete process of pipeline production is described. In the PP process four main steps can be distinguished: pre-production, welding, NDT, and FJC.

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2.2 Process description A schematic overview of these four steps can be seen in figure 2.1. The first step pre-production takes place before the FL. The other three steps combined form the FL.

Pipeline production process Firing Line

Non distructive testing

Welding Field Joint

Coating Pre-production

Figure 2.1: Scematic overview of the process

Each of the steps is performed in a separate work station. Table 2.1 gives an overview of the number of stations on each of the PLV’s of Allseas. The number of stations used depends on the project. For smaller pipeline OD’s with smaller wall thicknesses (WT) less welding stations could be used than there are available.

Vessel Welding stations NDT stations FJC stations

Pieter Schelte 6 1 6

Solitaire 5 1 4

Audacia 7 1 3

Lorelay 6 1 3

Tog Mor 3 1 1

Table 2.1: Firing line stations overview

In the next sections the processes during pre-production and in stations in the FL are further explained.

2.2.1 Pre-production

The pipeline is produced in the FL, before the FL there is a pre-production process. In this pre-production process the joints that form the pipeline are prepared for the process of the firing line.

The steps in the pre-production process are bevelling of the joint, cleaning of the inside of the joint and finally heating of the ends of the joint. These steps can be seen

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in the schematic overview in figure 2.2. Pre-production P ro ce ss st e p Cleaning Beveling Heating

Figure 2.2: Process of pre-production

Joints come in a standard length of 40 feet (12.2 meter). Joints come in different sizes with respect to OD and WT [8]. The choice for OD and WT are based on the function of the pipeline. These functions can be roughly divided into three categories as shown in table 2.2. These are not set values. Other combinations are possible as well.

Type OD [inch] Length [km]

Infield 6 - 12 1 - 30

Trunk lines 10 - 24 10 - 70

Export lines 24 - 42 100 - 1000

Table 2.2: Joint types

Joints are made of steel and WT ranges from 12 to 41 mm. Joints are supplied with a factory applied coating which is called the parent coating. The ends of the joints are left bare for welding and NDT. This bare end is called a cut-back. The length of the cut-back ranges from 100 to 250 mm.

Joints are supplied by different companies depending on the job location. The way joints are transported, stored and handled form supplier to the vessel has led to many different surface conditions of the cut-back. These conditions can range from mild rust to severe pitting. Severe corrosion on the cut-back has a negative effect on the time needed to prepare it for the FL.

The first step is making a bevel. Depending on the type of weld two different bevels can be made. If the joint is welded from the inside and the outside a so called K-bevel is made. Welding from the inside can only be done in the DJF. If the joint is only

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2.2 Process description welded from the outside a so called J-bevel is made. In the FL the FJ is only welded from the outside. In figure 2.3 an example of both bevels can be seen.

Figure 2.3: Example of a J-bevel and a K-bevel

To make the bevel a machine is inserted in the pipe. It machines the edge of the cutback in the required bevel. The machine also brushes the cutback to prepare it for welding.

After bevelling the joint is cleaned from the inside. This is done to prevent foreign objects being left in the pipeline during or after production.

Once the joint is cleaned the cut-back is heated with a heating coil. This is done to prepare for the welding process in the FL. After heating the joint can enter the FL.

2.2.2 Welding Welding S ta ti o n P ro ce ss st e p Intermediate stations (2-4/ 5/6) Bead stall (Line-up station 1) Final station (5/6/7)

Filler (hot) pass

Root pass Cap weld

Figure 2.4: Process of welding

Before welding starts, the new joint is lined up against the existing pipeline. This is done with a line-up car. The line-up car is controlled by an operator. The operator

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can manoeuvre the joint in all directions. When the joint is lined-up correctly the first weld is made. The first weld is called the root pass. The root pass is a full pass around the circumference of the pipe. This weld must be strong enough to withstand the forces of a pull. After the root pas, the next stations make the filler (hot) pass. In the final welding station the last weld is laid which is called the cap. The steps of the welding process can be seen in figure 2.4. The build-up of the welds can be seen in figure 2.5.

Figure 2.5: Build-up of welds in the pipeline wall

The number of welding stations used is based on the amount of welding that needs to be done. This in turn depends on the WT and OD of the pipeline. The first (root pass) and the final (cap) welding station are a given. The number of stations in between depends on the amount of welding that has to be done. It is distributed over these stations so none of them can be critical. Cycle times of the first or last welding station are leading. In each station welding is done until the pull can be made. When a pull can be made the particular station stops welding and marks the end point. The next weld station then resumes welding from the spot the previous station has marked. Once the final weld is made, the whole weld has to be checked for defects in the next station.

2.2.3 Non-destructive testing

After welding the quality of the weld must be checked. This is done in the NDT station. In the past this was done with X-ray, when photos were made of the weld. These photos were then inspected. The downside of these photos was their size: they were the same scale as the weld itself.

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2.2 Process description X-ray testing has now been replaced with automatic ultrasonic testing (AUT). With AUT the images appear on computer screens and can be enhanced for a more detailed view. AUT works with sound waves that penetrate the metal trough water as a coupling medium. This water also cools the FJ, which is still hot from the welding process. After leaving the NDT station the FJ temperature is around 120 degrees Celsius.

The AUT device moves on a rail along the circumference of the pipe. The results can be seen instantly on computer screens. If unacceptable weld defects are detected they must be repaired. A partial section or the whole joint can be cut out for repairs. If a repair has to be made, overall production time is greatly affected. The pipeline has to be pulled in and the repair has to be made. This results in the loss of valuable production time.

If the weld passes NDT it can progress to the next station where the FJC application process starts.

2.2.4 Field joint coating - FBE

The application of FBE as a field joint coating is a three step process. In the first step the surface area of the FJ is prepared. In the second step the FJ is heated. The final step is the application of the FBE coating. These steps can be seen in figure 2.6. In figure 2.7 a typical layout of a FJ can be seen.

Multiple stations are available for coating application. The first station is for surface preparation. The second station is for the application of the anti-corrosion coating. Other stations can be used for secondary coatings. As mentioned in chapter 1 these lay outside of the scope of this research.

Grit blasting is the process where a blast medium is accelerated by compressed air against the FJ. This takes place in the first FJC station. Once the FJ has been blasted a protective sleeve is applied around the FJ. This is done to protect the cleaned surface while it goes through the tensioner to the next station.

In the next FJC station the FBE coating is applied. This is a two-step process that takes place in the same station.

For the application of FBE coating the FJ needs to be heated to a certain temper-ature. This is done with an induction coil. Once the required temperature is reached the coil is taken off. The coating frame is then put on the pipe. This switching of equipment takes time. Once the coating is applied the coating frame can be taken off.

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Field Joint Coating (FBE) S ta ti o n P ro ce ss s te p Station Coating application 1 Surface preparation FBE coating application Induction heating Grit blasting

Figure 2.6: Schematic process overview of Field Joint Coating

Figure 2.7: Typical field joint

If necessary the coating can be cured by pouring water over the FJ. This is done by placing a clamp with a water hose on top of the pipe.

2.3 Cycle time analysis

When a new tender for a project is prepared within Allseas, employees from the Pipeline Production Departement (PPD) make an estimate of the total process time. This estimate is based on the cycle times of each of the process steps as described in this

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2.3 Cycle time analysis chapter. From interviews with employees from PPD it became clear that the estimate is not really based on databases with project data but more on experience. This meant it was difficult to obtain data regarding cycle times.

Based on the limited available date from a number of projects the cycle times per process step are summarised in table 2.3. Projects are named letters A to G. From this data it can be seen that the FJC process step can become critical.

( critical ) OD Welding NDT FJC

Project [inch] [sec] [sec] [sec]

A 24 501 180 505 B 18 215 150 156 C 18 145 150 156 D 18 142 135 136 E 18 178 150 178 F 13 233 150 175 G 20 188 150 178

Table 2.3: Cycle times of the three main steps

From the projects in table 2.3 where FJC station were critical there was more data available regarding cycle times of the individual stations. For two other projects H and I also data was available with respect to cycle times of the FJC stations. These cycle times are summarised in table 2.4.

( critical ) OD Surface prep Coating Heat Coat

Project [inch] [sec] [sec] [sec] [sec]

A 24 180 230 160 70

C 18 96 95 55 40

E 18 143 178 104 74

H 36 200 285 180 105

I 18 151 134 67 67

Table 2.4: Cycle times per station

From the cycle times from tabel 2.4 it can be seen that both the surface preparation station and the coating application station can become critical.

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From this limited amount of data it can be concluded that changes to the FJC process and its stations could have an effect on overall process times.

2.4 Conclusions

From the analysis of the current method of pipeline production it can be concluded that there are three possibilities for changes to the process that could have an effect on the overall process time.

• The order of steps within the process • Combination of steps within the process • Alternative methods within the process step

Although limited, an analysis of cycle times showed that this would indeed have an effect.

The three possibilities for change are further researched in chapter 4. Before this can be done an analysis of the current methods within each of the process steps of FJC must be made, which is done in the next chapter.

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3

Analysis - equipment

In this chapter an analysis is made of the current equipment that is used for the application of FBE as a FJC. In section 3.1 requirements are given for the application equipment. Surface preparation is analysed in section 3.2. Coating application is analysed in section 3.3. Finally in section 3.4 conclusions on possibilities for changes are drawn based on the analysis.

3.1 Requirements for equipment

In this section the requirements for existing equipment are described. These require-ments can also be used when developing new equipment.

Quality As with the process, the use of specific equipment should result in a agreed level of coating quality. This level of quality is agreed upon by clients of Allseas and Allseas themselves. It is described in client specifications. In these client specifications it is stated which equipment should be used and which procedures should be followed to assure an acceptable quality level of the coating.

Before the project is executed offshore, Allseas performs a Procedure Qualification Trial (PQT). During a PQT Allseas shows the client in which manner the coating is applied. After the coating is applied it must be shown that the agreed level of coatin quality is achieved. For this purpose the applied coating is subjected to quality tests as described in specific norms and standards. For FBE coating the quality tests as described in ISO norms 21809 and 8501-1 are performed.

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Practical The available space on board the vessels is limited. This means equipment must be kept within certain dimensions to fit inside the FL or storage areas. The same holds for consumables used by the equipment.

The possibility to implement a new alternative based on current machinery and infrastructure is an advantage. Extensive changes to the vessels layout to fit equipment are not desirable, unless this could be justified with the performance of the equipment.

Financial Operational costs for equipment should be minimised. These costs come from:

• Building the equipment: cost of development and costs of components • The transport and use of consumables

• Operators of the equipment

• Energy consumption of the equipment

With new equipment, investments must be made. If operators have to operate new equipment, investment in training must be done as well.

Safety and Health Operator safety is an important issue when using equipment. The QHSE department has the specific task to ensure equipment can be used in a safe manner. When designing or buying new equipment the safety aspect must be kept in mind.

3.2 Surface preparation

Prior to the application of the anti-corrosion coating, the surface of the FJ needs to be cleaned. In this preparation the surface is cleaned and corrosion is removed. Depending on the type of coating there are different methods with different results. Anchor profile and surface cleanliness are leading in the choice for which method. Allseas uses two methods, power wire brushing or grit blasting.

Currently for the application of FBE the surface is always prepared with grit blast-ing. Grit blasting is the process in which grit is propelled at a high velocity by way of pressurized air against the substrate. Due to the shape and speed of the grit this has

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3.2 Surface preparation an abrasive effect. Depending on the conditions of the FJ the grit blaster is capable of cleaning up to 20 m2/hr [10].

The goal of grit blasting is to get a surface that is: • clean: cleanliness of SA 2.5

• rough: anchor profile created of 32-100 microns

These are two important requirements. The cleanliness is defined by the ISO norm 8501-1, where SA 2.5 stands for: Mill scale, rust paint and foreign matter are removed completely. Any remaining traces are visible only as slight stains or discoloration in the form of spots or stripes. The anchor profile is a measurement of the roughness of the surface. This is measured from the lowest point to the highest point of the surface. In figure 3.1 two examples of surface roughness can be seen.

Figure 3.1: Anchor profiles on substrate; left is shallow, right is deep[1]

Clients of Allseas for the most part specifically request for the grit blaster to be used as a method of surface preparation if FBE is used as a coating.

3.2.1 Blast media

The blast media used for grit blasting is a mix between shot and grit. Shot particles have a rounder shape and act as a cleaner. Grit particles have sharper edges that create the required anchor profile. The correct mix between the two components is important. Blast media has a limited life time as it deteriorates due to impact forces. This means that during a project Allseas has to carry sufficient blast media on board the vessel.

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Since the blast media that Allseas uses is made of steel particles it has to be stored under controlled circumstance to prevent corrosion.

A sample of the blast media Allseas uses can be seen in figure 3.2.

Figure 3.2: Sample of blast media: steel shot and grit mix

3.2.2 Blast frame

Allseas developed an automatic frame in which two grit blasting heads are mounted. The blast heads are positions opposite of each other. Each cleans one half of the FJ. The heads can rotate and translate around the FJ [11]. This is done with electric motors which are controlled by a control panel where the speed in both directions can be pre-set. The frame is presented in figure 3.3.

The blast head is a closed loop system: a combination a nozzle and a suction part. The nozzle ejects the grit; the suction part surrounding the nozzle removes the grit mixed with dust particles. The used grit is sucked away to be filter and re-used.

During a noise survey on board PLV Lorelay measurements were taken on multiple locations in the FL during production. These measurements were taken by a third party. Results from these measurement show that for the grit blaster noise levels of 97 dB were reached [12]. To protect operators double hearing protection was advised. The QHSE department within Allseas also expressed their wishes for a reduction of noise levels from the grit blast equipment.

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3.2 Surface preparation

Figure 3.3: Grit blast frame in operation on the pipe

In recent projects there were signals that the grit blast process would be critical. To speed up the cycle time of grit blasting two additional heads were fitted to the blast frame. This led to lower cycle times but created another problem which is described in section 3.2.3. Exact cycle times could not be found, but interviews with Allseas employees confirmed the reduction of cycle times when using four blast heads instead of two.

3.2.3 Grit handling units

The grit is processed in the grit handling units. These units are made by LTC. Therefore they are named LTCs. In figure 3.4 an LTC can be seen.

In the LTC dust and rust particles are separated from returning stream of grit. The cleaned grit is then mixed with the compressed air and fed back to the blast heads in blast frames.

With the addition of more blast heads, more LTCs were needed. The capacity of the existing LTCs was not sufficient. This created a problem since the LTCs are placed in the so called Green Mile where space is already limited.

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Figure 3.4: Grit handling unit - LTC

The Green Mile is a hallway situated alongside the FL. It is used by personnel to reach the different stations. It is also used to store other equipment and consumables. During pipeline production this normally is a crowded area. In figure 3.5 the green mile of PLV Solitaire can be seen.

When new equipment is introduced within the PP process the availability of space is an important matter to take into account.

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3.3 Coating application

Figure 3.5: Green mile of PLV Solitaire

3.3 Coating application

After the surface preparation mentioned in section 3.2 the anti-corrosion coating can be applied in the next station. In the coating station, multiple machines are used in a sequence.

3.3.1 Heating coil

Prior to the application of FBE and HSS it is necessary to heat up the FJ. FBE requires a temperature in the order of 230 degrees Celsius, while the application of HSS needs a lower temperature of 180 degrees Celsius.

To achieve this temperature an induction heating coil [2] is used. This coil is wound around the FJ and a large AC current goes through. The AC current has a frequency of 2000 to 3000 Hz. The power is in the order of 100 to 500 kW.

The generated heat comes from the eddy currents which flow through the pipe as a reaction on the electromagnetic field the coil creates. In figure 3.6 a heating coil can

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be seen. The thick red leads form the actual coil. The frame encloses the leads around the FJ.

Figure 3.6: Heating coil

Induction heating is the most efficient and clean way of heating the pipe[13]. The shape of the coil determines the heating profile generated in the pipe. Due to the parent coating (factory applied coating) on the joint it is necessary to maintain the heated zone within the FJ. If the heated zone is greater than the width of the FJ the parent coating can be damaged by the generated heat. This will result in bad adhesion of parent coating to the pipe or parent coating to the applied coating. A schematic overview of the heat profile along the FJ can be seen in figure 3.7.

3.3.2 Fusion-bonded epoxy

Fusion-bonded epoxy is a one-part thermosetting epoxy resin powder that uses heat to melt, crosslink and adhere to the metal substrate [14]. FBE being one part means no solvents are involved. During the manufacturing of FBE the resin and the curing agent are pre-mixed. The reaction between the two is incomplete and continues when the resin is reheated during the FJC application process.

FBE has a number of properties which are suited for pipeline coating: • Physical and chemical stability

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3.3 Coating application

Figure 3.7: Heat profile along the field joint[2]

• Adhesion and resistance to impact • Resistance to cathodic disbondment

When FBE is used as a coating the required thickness can vary between 300 and 500 microns. The choice for the applied thickness depends on the function of the coating. FBE can be the only coating which will be applied to the FJ. The thickness of choice will then be in the order of 500 microns. If FBE is applied as an anti-corrosion coating where more layers of other types of coating will be applied, the thickness will be in the order of 300 microns.

3.3.3 Coating machine

The coating machine is used to apply coating. The complete coating machine is made up of two parts. The first part is the automatic spraying frame. The second part is the fluidised bed, which supplies the frame with FBE powder.

Application frame

The spraying of FBE powder is done by standard spray nozzles. These nozzles are fitted in a ring that spans over the circumference of the FJ[15]. The ring moves along

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the pipe and rotates with increments. The movement is controlled by a program, which is set to apply the required coating thickness.

In figure 3.8 the frame can be seen.

Figure 3.8: FBE coating frame

Due to the lay-out of the nozzles in the ring there is an overlap in powder streams. This ensures a full coverage of the FJ, but more FBE powder is sprayed than necessary. The ring is equipped with an extraction system for the excess powder. The inside of the ring can be seen in figure 3.9. In the centre the nozzles are placed. On both sides the extraction hoses are placed. The problem of excess spraying will not be further investigated in this research. From interviews with Allseas employees it became clear that this problem does not have a negative effect on cycle times.

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3.4 Conclusions Fluidised bed

The fluidised bed gives the FBE powder the characteristics of a fluid so it can be applied to the FJ. A fluidized bed is a drum where pressurised air (2.5 bars) is blown in from the bottom through a mesh. The mix of air and powder has fluid properties. Via a venturi pump the powder is transported through hoses to the spray nozzles. When FBE application starts the operator opens the electromagnetic controlled valves on top of the barrel so the powder can flow to the nozzle.

Figure 3.10 shows the fluidised bed together with the control panel. The barrel can be seen behind the control panel in this figure.

Figure 3.10: Fluidised bed together with control panel

3.4 Conclusions

From the analysis of the equipment used for FJC application of FBE a number of conclusions can be drawn.

For surface preparation grit blasting is an effective method for reaching the de-sired anchor profile and cleanliness. However there are a number of possibilities for improvements:

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• Noise level of the grit blaster • Usage of consumables (blast media)

• The required space for supporting equipment (LTCs)

Regarding the heating of the FJ, the principle of induction heating is the most suitable. A possibility for change could lie in the shape of the coil. If the shape of the current induction coil could be changed it could be possible to combine the coil with other process steps.

These possibilities for change will be further explored in the next chapter. There they will be combined with the conclusions regarding the process from chapter 2 to find possible alternative application methods.

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4

Alternative application methods

In this chapter possible alternative application methods are explored. The alternatives are based on the possibilities for improvement as identified in chapter 2 and chapter 3. Alternatives for the process of FJC are explored in section 4.1. Alternatives for surface preparation are given in section 4.2. In section 4.3 alternatives for coating application are given. In section 4.4 alternatives application methods are formed based on the findings of section 4.1 , section 4.2 and section 4.3. Finally in section 4.5 conclusions are drawn based on the formed alternative application methods.

4.1 Process alternatives

From the analysis of chapter 2 two possibilities for changes of the process were found. The order of steps within the process or the combination of steps within the process could be changed. In this section both options are further explored.

4.1.1 The order of steps within the process

Following the dismantling of the mechanical blast installation there were ideas within Allseas to re-use the equipment in a different way. The main idea was to salvage the parts of the old machine and come up with a machine that could blast the cutbacks of the joints prior to the entry in the FL. In the FL the joint would be blasted again with the conventional air pressured grit blaster. This would effectively mean a two stage blasting process. A schematic overview of the process can be seen in figure 4.1.

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Pipeline production – two stage blasting Firing Line

Non distructive testing

Welding Field Joint

Coating Pre-production Surface preparation – anchor profile Surface preparation - clean

Figure 4.1: Pre-blast process

In this process the pre-blast would create an anchor profile. During the processes of the FL the FJ gets contaminated with weld spatter and NDT water. So therefore just before heating and coating another blast sequence should be implemented to clean the FJ again. As the anchor profile was already created this second blast step could be done quicker. The parts of the old mechanical grit blast machine proved not to be useful again.

Tests were done with the pre-blasting concept. In these tests the conventional air pressured grit blaster was used for both stages. In these tests it was concluded that a time reduction of up to 30 % was achievable[10]. After these tests there has not been a follow up with the actual application of coating or the research of the possibility of implementing this.

Therefore the option of pre-blasting should be further explored. It could be possible to use different methods for creating the anchor profile and cleaning of the field joint. An important factor that must be incorporated within the pre-blast process is the weld surface. When the joint is pre-blasted there is an anchor profile on the cut-back. Once two joints are welded there is no anchor profile on the weld surface. During cleaning in the FL it should therefore be possible to make an anchor profile.

Possible methods that could be used in the pre-blast process are further explored in section 4.2.

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4.1 Process alternatives

4.1.2 Combination of steps within the process

In the application process of FBE there are three steps that can be distinguished, surface preparation, heat and coating. Due to the layout of each of the FL it is only possible to combine the heat and coat steps. In the FL the surface preparation station lies before the tensioner while the heat and coat station lies after the tensioner. Coating before the tensioner is impossible due to the fact that the tensioner would destroy the freshly applied coating. Heating before the tensioner would melt the friction pads and possibly more components of the tensioner itself.

Figure 4.2: FBE application dishes

The possible combination of heat and coat has been tried by Allseas in 2004. A combined heat and coat machine was designed and built. A schematic view of the process with the combined heat and coat machine can be seen in figure 4.3.

At that time FBE was applied by oval dishes instead of the now used nozzles. These oval dishes had an advantage of being low profile and thus could be positioned between the pipe and the heating coil as can be seen in figure 4.2. The dishes however had a negative effect on coating quality. They were incapable of applying a constant quality of FBE coating.

Next to that the dishes deteriorated during operation because of friction between the FBE powder and the dishes. This resulted in unwanted downtime due to repair and maintenance. Another downside of this combination was the overspray of FBE which

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Field Joint Coating S ta ti o n P ro ce ss st e p Coating application 1 Surface preparation Coating application 2 Combined Heat & coat

machine

Figure 4.3: Combined steps process for heat and coat machine

nested itself on the heating coil and its parts. Mainly affecting the copper contact blocks that close the current loop of the induction coil as shown in figure 4.4. The build-up of FBE rendered them useless after a number of cycles, leading to more downtime due to replacement.

Figure 4.4: Contact blocks of heat and coat machine

Two distinct upsides to this combination however were the elimination of the change-over time from the heating coil to the coating frame. Next to that the heating

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4.2 Surface preparation alternatives coil could be set to a lower temperature as it was not necessary to compensate for the heat loss during change-over.

Recently Allseas has changed the application of coating from dishes to nozzles. From interviews with Allseas personnel it became clear that dishes are no longer preferred as the nozzles perform much better. This makes building a combined heat and coat machine impossible. Nozzles need a certain distance from the object on which they spray for a cone to form which applies an even layer of coating. This distance is not present between the heating coil and the pipe as can be seen in figure 4.5.

Figure 4.5: Spacing between the heating coil and pipe

It can be concluded that with the adaptation of current equipment it is not possible to build a combined heat and coat machine. For this purpose new methods of heating and coating application should be further explored.

4.2 Surface preparation alternatives

Based on the conclusions from section 4.1 in this section possible alternative methods are further explored with respect to surface preparation.

4.2.1 Mechanical blasting

Mechanical grit blasting is a method of surface preparation in which the abrasive media is propelled to the substrate. This is done by wheel that is driven by either an electric

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or a hydraulic motor. The flow of blast media is regulated with an impeller in the centre of the throwing wheel. The blast media is fed into the impeller through a chute. A mechanical blaster can be seen in figure 4.6. The main advantage of mechanical blasting is the simplicity of the machine with respect to a conventional air pressured grit blaster.

Figure 4.6: Mechanical blasting machine [3]

Allseas has tried to incorporate such a system in 2005. This mechanical blaster was fitted in the firing line as a permanent installation. It used six electric motors driving six wheels that propelled the blast media at the FJ. This can be seen in figure 4.7

Although a good anchor profile was created, the system was not a success. Due to difficulties with reclaiming of the blast media and the stationary character in de FL in which the pipe could move to a certain degree with respect to ship motions, the machine was discontinued.

When incorporated before the firing line it can be possible to make a stationary mechanical blaster where the joint rotates. This approach will result in a simpler mechanical blaster than the one used in the FL. This would make the mechanical blaster an option for the pre-blast process.

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4.2 Surface preparation alternatives

Figure 4.7: Bauhaus mechanical blaster in FL

4.2.2 Laser blasting

Surface treatment with laser is a technique which is mostly applied in the aviation industry. It is possible to clean metal surfaces with a powerful laser. The principle behind this is shown in figure 4.8. The pulsating energy of the laser beam makes it possible to treat the surface area. The amount of substrate material that is removed depends on the intensity and the frequency of the pulsations of the beam.

This technique was introduced to Allseas in the past through a demonstration. In the demonstration a limited number of steel plates cut from actual joints were treated as shown in figure 4.9. The demonstration showed that it would be possible to clean rusted steel surfaces although it was mentioned that it was not possible to create an anchor profile.

These conclusions were later backed by a research done by Mitraco, another com-pany involved in laser blasting. Mitraco did a study into the implementation of laser blasting within Allseas. In the study it was stated that it was not possible to achieve a certain anchor profile, but it would still be possible to get the desired coating quality[16]. Another company (SLCR) however claims that an anchor profile can be created. Due to recent developments in laser technology, faster cleaning process time can also

The application process of fusionbonded epoxy as field joint coating - Het applicatie proces van fusion-bonded epoxy als field joint coating