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THE INFLUENCE OF OFFSHORE AND SHIPBOARD CABLES STANDARDIZATION ON PLATFORM CONSTRUCTION GUIDELINES AND

LOCAL MARKET

Copyright IEEE

Thiago Trezza Borges Michael da Fonseca Pinheiro Waldir de Melo Mota Junior Petrobras Petrobras Petrobras Av. Almirante Barroso 81 Av. Almirante Barroso 81 Av. Almirante Barroso 81 Rio de Janeiro, 20031-004 Rio de Janeiro, 20031-912 Rio de Janeiro, 20031-912 Brasil Brasil Brasil thiagoborges@petrobras.com.br michael@petrobras.com.br waldirmota@petrobras.com.br

Abstract – In 1992 the Brazilian state owned oil & gas company established standards for offshore electrical cables. After some years, these documents became outdated and didn’t comply with international standards. Then the company decided to cancel these internal documents and use international standards in order to specify these materials. Moreover, in order to minimize its expenses, the company decided to use off the shelf and less customized equipment in its projects. Therefore in 2009 the company decided to create standard technical specifications according to international standards of offshore cables, including IEC 61892-4 [2]. This IEC standard was unknown to the technicians and engineers of the company and the local market. Further, these new standard specifications considered new cable construction technologies (e.g. Mud resistant cables). The paper objectives are to disseminate this learning and share the knowledge gained through the research of international standards and technical consultations to manufacturers. It is expected that those actions will reduce the purchasing costs of offshore electrical cables. This study resulted in the update of the offshore units construction guidelines.

Index Terms — Cable Specification, Offshore Platform

Cables, Material Standardization

I. INTRODUCTION

Electrical cables are used to transport energy in generation, transmission and distribution power systems. According to [1] ,the cables are basically composed of four main elements:

− conductor; − dielectric system; − shield system; − external protection.

The conductor, the element that transports energy, is

normally made of copper or aluminum. It can be made using one wire or multiple wires (strands).

The dielectric system is composed of two parts: insulation and insulation shield. In low voltage cable design the insulation shield is not used.

The shield system is used to ensure an equalized distribution of electrical stress around the conductor and protect it against interference, mainly electromagnetic.

The external protection is to protect the cable in installations where it may suffer mechanical damages. It can be made of a simple extruded polymeric layer, wires, metallic braids or a metallic sheath.

The cable construction depends on the correct specification of each element. A wrong or inadequate cable specification can cause many problems, as follow:

− raise acquisition costs; − delay cable delivery; − problems in bid process; − electrical accidents.

In 1992 the company established two standards for

power and instrumentation offshore electrical cables: MARINE ELECTRICAL CABLE FOR OIL OFFSHORE PLATFORMS and ELECTRIC INSTRUMENTATION CABLE. These standards were referenced in a document called “Platform construction guidelines”. These guidelines were settled to establish minimal requirements to construct an offshore unit.

After some years, these documents became outdated and didn`t comply with international standards. It caused many problems because the manufacturers were driven to make cables which were different from the industrial standard.

Moreover, in order to minimize its expenses, the company decided to use off the shelf and less customized equipment in the projects. So, from now on, the platform guidelines only mention international standards in order to specify the cables.

In 2009, the company decided to create a standardization program to study all these international standards and create a specification of most commonly used cables. The main objectives of this program are:

− create a list of standard cables; − improve the cable buying description; − erase the wrong items in the register; − order off the shelf cables;

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− improve the technicians knowledge on the cable construction and specification.

This paper presents the acquired knowledge in studies

and research of international standards and manufacturer technical consultations. It allows the company technicians to improve their knowledge about electrical cable specification.

II. THE STANDARDIZATION PROGRAM The Standardization Program aims to integrate the

company efforts on the activity of materials standardization in conjunction with areas such as Materials, Engineering, Exploration, Refining, Energy and Logistics. This program promotes the standardization of material descriptions, reducing the variety and integration of engineering standards used by the company. The program does not intend to work with technological innovation, but with existing technologies which are already mastered and consolidated in the Company.

The expected products of the program are: − Standard Technical Specifications and Data

Sheets; − Standard Tags in the "Material Management"

catalog of the Integrated Information System; − Revision of internal standards − Bill of Standard materials.

The Main Expected Benefits:

− Reduction of efforts in the design phases and solving problems in engineering, operation and maintenance;

− Decrease in prices and terms of acquisition (productivity) and consequent reduction in the building time;

− Alignment with industry supply installed in the country, strengthening the level of national content.

The standardization process is divided in six main steps:

− Planning Step: define the material that will be studied and create a project plan and preliminary activity schedule;

− Kickoff Meeting: project plan and activities schedule is presented to the group. It is also decided which suppliers will be invited to the suppliers workshop;

− Task Force: the members of the group define the specification draft based on suppliers workshop and national and international standards;

− Users Consultation: the documentation is sent to all company users in order to verify if the standard complies with their applications;

− Validation: all the user suggestions are analyzed and a final version of the specification is written;

− Material Classification: the standard material is registered in the Material Management System. The system assigns a number for each material.

This number is referenced in the technical specification.

Fig. 1 Standardization process

III. STANDARD CABLE SPECIFICATION

At the beginning of the study the group became aware of

an IEC (International Electrotechnical Commission) standard that was unknown to by many of the company specialists: IEC 61892-4 (Mobile and fixed offshore units – Electrical installations – Part 4: Cables). It specifies the requirements for the choice and installation of electrical cables intended for fixed electrical systems in mobile and fixed offshore units. This includes pumping or “pigging” stations, compressor stations and exposed location single buoy moorings, used in the offshore petroleum industry for drilling, production, processing and for storage purposes. The IEC 61892-4 references IEC 60092 series [3], [4] in order to specify the cable characteristics such as conductor, insulation, etc. Also, this new standard was included in the construction guidelines document.

In this standardization program the specification of power cables used in offshore units was studied.

A power cable has the following characteristics, according to Figure 2

1 – Conductor

2 – Conductor Shield

3 - Insulation

4 – Non-metallic shield insulation

5 – Metallic shield insulation

6 – Filler

7 – Inner sheath

8 – Amour

9 – Sheath

Fig. 2 Cable construction characteristics

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Beyond specifying the cable construction characteristics,

a power electrical cable has two additional characteristics: rated voltage and ampacity.

1) Rated Voltage The electric cable rated voltage is the voltage between

conductor and earth or insulation shield (Uo) and the voltage between conductors (U). So according to IEC standards the cables are specified by the Uo/U value. The maximum system operation voltage (Um) might be included in the specification, but it is not very common.

The rated voltage defines the insulation material thickness and the values of Uo, U and Um should be based on the characteristics of the system.

The standard rated voltages specified are: − Low voltage cables: 0,6/1 kV; − High voltage cables: 3,6/ 6 kV, 8,7/15 kV, 12/20

kV. 2) Ampacity Ampacity is the maximum amount of electrical current a

conductor can carry before sustaining immediate or progressive deterioration. Also described as current rating or current-carrying capacity, ampacity is the RMS electric current which a device can continuously carry while remaining within its temperature rating. The ampacity of a cable depends on:

− its insulation temperature rating; − the electrical resistance of the cable material; − frequency of the current, in the case of

alternating current; − ability to dissipate heat, which depends on cable

geometry and its surroundings; − ambient temperature.

3) Conductor The conductor is a metallic product having invariant cross

section, used to transmit electric energy or signals. Normally it is made by copper (tinned or not) or aluminum. The choice of conductor material should be made considering the ampacity, dimension limitation, weight, corrosion aspects, voltage drop and cost.

Due to aggressive offshore units environments (e.g. salt), the company decided to use only tinned copper conductors because it is resistant to corrosion.

4) Conductor Shield The main purpose of this shield is to give a perfectly

cylindrical shape to the conductor and to eliminate spaces between the conductor and insulation. If a medium or high voltage conductor has no semiconductor material overlap, the electric field assumes a distorted shape following the surface of the conductor. In this condition a non-uniform electric field is applied to in the insulation. This can exceed the acceptable limits for the dielectric, causing a reduction in the cable lifetime.

Therefore, the shielding of the conductor must be used in electric cables with voltage insulation above 3.6 / 6 kV. The shield must be non-metallic, consisting of a layer of extruded compound semiconductor, or a combination of textile ribbon with an extruded semiconducting layer. For cables with electrical insulation under or equal to 3.6 / 6 kV the application of a shield is optional, allowing those cases to be made of semiconducting textile tape. In all cases, the material used must be compatible chemically and thermally, with the conductor and the insulation.

5) Insulation Polymeric insulators or solid dielectrics are materials

composed of macromolecules. They are known as homopolymers when they are formed by molecules of the same species and copolymers when they consist of a combination of different molecules. Depending on their thermomechanical behavior, they can be classified as thermosetting and thermoplastics.

Thermoplastics are obtained directly by extrusion of the compound. They are materials that, when subjected to a gradual increase in temperature, they continue in solid state until about 105 °C to 130 °C . From this temperature, they lose their mechanical properties and soften until they become liquid.

Thermosets are obtained from the extrusion and crosslinking (vulcanization) of the compound. They are characterized by maintaining their physical condition even in regimes where high temperatures are involved (when the temperature is raised beyond the permissible limit) to carbonize the material without becoming liquid. The excellent thermal stability of thermosetting allows more power to be transported by the same section of conductor than similar thermoplastic.

Table I shows the conventional insulations and non-halogenated (HF - Halogen-Free) from IEC 60092-351.

TABLE I

TYPES OF INSULATION

Type of insulating compound Abbreviated designation

Based upon polyvinyl chloride or copolymer of vinyl chloride and vinyl acetate

PVC

Based upon ethylene-propylene rubber or similar (EPM or EPDM) EPR

Based upon high modulus or hard grade ethylene propylene rubber HEPR

Based upon cross-linked polyethylene XLPE Based upon silicone rubber S 95 Based upon ethylene-propylene rubber or similar (EPM or EPDM) halogen-free

HF EPR

Based upon high modulus or hard grade halogen-free ethylene propylene rubber

HF HEPR

Based upon halogen-free cross-linked polyethylene HF XLPE

Based upon halogen-free silicone rubber HF S 95

Based upon cross-linked polyolefin HF 90

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material for halogen-free cables According to IEC 61892-4 [2], cables for installation in

accommodation spaces and passenger areas shall be of low smoke /zero halogen construction. In order to reduce the number of cable types, the company decided to specify only halogen free cables.

After the agreement with the consulted cables manufactures, the company decided to standardize the HF XLPE compound for the insulation.

6) Insulation Shield This shield has a primary function of providing radial and

symmetric distribution for the electric field, in order to prevent internal and external interference. Another function is to provide a uniform capacitance between conductor and earth, which represents uniform impedance along the electrical cable, avoiding reflection points and providing better performance in impulse situation.

The insulation shield, formed in the non-metallic (semiconducting part) and metallic part, should be used in electric cables with rated voltage up to 3.6 / 6 kV. For cables with rated voltage under or equal to 3.6 / 6 kV, this shield is optional.

For the insulation shield to be effective, it must maintain perfect contact with the outer surface of the insulation, thus eliminating the possibility of bubbles and imperfections that would facilitate the emergence of partial discharges.

7) Inner Sheath and fillers As the use of cable glands for electrical wires, for

example, it is necessary that the cross section of the electrical cable be circular. So it is applied inside electric cables covers and fillings in, more than one conductor, in order to ensure the circular cross section.

8) Metallic Armor In order to protect the electric cables in case of

mechanical damage, they may have a metallic armor. The materials provided in the IEC standards are: steel, galvanized steel, lead, aluminum, aluminum alloy, copper or copper alloy and may consist of:

− flat wires; − round wires; − two flat strip; − conformed and interlocked tape.

The metallic armor standardized for offshore cables is

galvanized steel round wires braid. 9) Sheath The cable should have a non-metallic sheath made by

thermoplastic or thermosetting polymers defined in IEC 60092-359 [4]. The type of sheath material should be compatible with the conductor operating temperature and compatible chemically and thermally with the insulation material.

Table II shows the sheath materials that can be used in offshore cables.

TABLE II SHEATH MATERIALS

Type of sheathing compound Abbreviating designation

Thermoplastic: Based upon polyvinyl chloride or copolymer of vinylchloride and vinyl-acetate

ST1

Thermoplastic: Based upon polyvinyl chloride or copolymer of vinylchloride and vinyl-acetate

ST2

Thermoplastic: Halogen-free SHF1 Elastomeric or thermosetting: Based on polychloroprene rubber

SE1

Elastomeric or thermosetting: Based on chlorosulphonated polyethylene or chlorinated polyethylene rubber

SH

Elastomeric or thermosetting: Halogen-free

SHF2

After the agreement with the consulted cables

manufactures, the company decided to standardize on SHF1 compound for the sheath. It is chemical and thermal compatible with the insulation material (HF XLPE).

In places where the cables are subjected to hydrocarbons elements, the user should choose HF EPR for the insulation and SHF2 for the sheath. This situation is very particular and it was provided in the register system, but it was not standardized.

10) Performance of cables in the event of fire In order to determine the behavior of cables in case of

fire, a group of standards has been developed in order to establish conditions of fire and to measure the behavior of the cable in this situation.

- Flame retardant (Standard IEC 60332-1-1[5]): A

flame in contact with the sheath of the cable for an established period of time should not lead to propagation. This prevents the cable from being the origin of a fire caused by a minor incident or an external source of heat coming into contact with the cable.

- Flame spread (Standard IEC 60332-3-22 [6]): A fire unrelated to the cable can affect a cable tray (worst case if it is in a vertical position allowing air circulation creating the so-called chimney effect). If the decomposition temperature of the organic materials is reached, an exothermic combustion (with the contribution of energy) of the cables takes place with the consequent propagation of the fire. The insulation and sheath compounds can be formulated to make this exothermic reaction limited (by the addition of inhibitors). To simulate this situation, the test consists of the application of a high energy gas burner to a bunch of cables arranged to reproduce a vertical cable tray with forced air. Under those conditions, the fire provoked in the

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cables should extinguish within a time established in the standard. Based on the amount of combustible material per meter of bunch exposed to the fire action, the standard defines five different categories, and according to IEC 60092-350 being the mandatory one for shipbuilding/offshore applications Category A (IEC 60332 part 3-22).

- Zero halogen and low smoke cables (IEC 60754-1 [7] and 60754-2 [8] IEC 61034 -1&2 [9] and [10]): If the cables are immersed in a situation of fire and depending on the constituent materials, they can release gases which are toxic for the health of people or corrosive affecting the correct operation and preservation of the electronic and computer components in the vicinity. They can also release smoke which, due to its opacity, makes it difficult to see the escape routes from the spaces affected.

- Fire-resistant (Standard IEC 60331-21 [11]): For circuit integrity and all those systems which need to maintain service under fire conditions, there is the IEC 60331-21 standard where the fire conditions to which the cables are tested is defined, and which have to continue in service even if the fire has destroyed the organic parts of the cable. In the standard, the cable is exposed to a ribbon gas burner for a maximum of 120 minutes and at a minimum temperature of 830 °C, while being subjected every 5 minutes to shocks simulating debris fallout. During the test and at the end of it the cable has to maintain circuit integrity although all of its organic parts have disappeared.

All the standard cables should be Flame Retardant

(IEC- 60332-1-2 and IEC 60332-3-22) , Low Smoke (IEC 61034-1 e IEC 61034-2) and Zero Halogen (IEC 60754-1 and IEC 60754-2)

The Fire-resistant cables (IEC 60331) were not standardized, because they are not the most common application in the offshore units. They can be bought for a specific application.

IV. THE IMPACTS OF STANDARDIZATION PROGRAM IN LOCAL MARKET

Besides the technical gains due to standardization, the

program has brought positive impacts to local suppliers. The main impact is the cost reduction of production generated by the variety reduction of cables types and the consequent increase in the manufacture scale. The use to international standards also generated a positive impact on the local suppliers export capacity.

Another benefit of standardization was the approach between the company and the supplier market. It provided better interaction and exchange of information about the company's needs and manufacturer’s capabilities. This interaction resulted in improvements in the manufacturing process and in the product itself.

It is expected that there will be a reduction of the purchase price of the cables, due to cost reduction in manufacturing process and the competition among local and international suppliers. Moreover, it is expected that in future procurement processes have fewer questions compared to the previous cases, resulting in a reduction in the time of purchase, because the specifications are based on international standards.

The initiative to standardize the equipment and materials are aligned with company's intention to increase the level of local content of its acquisitions. Thereby the company contributes to the development of the country, because buying more in the local market, the local suppliers gain production scale. So they can reduce their selling prices, which generates a higher level of competitiveness and enables the reduction of imports.

V. CONCLUSIONS This paper presents a contribution for the specification of

offshore and shipboard electric cables. It specifies the entire constituent parts of the cable, showing its features and materials used. Moreover, the normative references have been indicated to facilitate the specification, testing and purchasing process.

Another result was the creation of a list of standard cables which are correctly specified, without technical inconsistencies. This allowed the reorganization of the material register database, avoiding mistakes in the process of acquiring cables.

A review of some items in the offshore guidelines document reflects the knowledge on this issue obtained from this project

Due to current demand, the company is carrying on studies to review the specification of the following type of electric cables

− BCS Cables [13] and [14]; − Cables for Intrinsic Safety Installations; − Field Bus cables;

IV. REFERENCES

[1] Teixeira Junior, Mario Daniel da Rocha, Cabos de energia, 2ª Ed., Artliber Editora, 2004.

[2] IEC 61892-4, Mobile and fixed offshore units – Electrical installations – Part 4: Cables Edition 1.0, June/2007.

[3] IEC 60092-351, Electrical installations in ships – Part 351: Insulating materials for shipboard and offshore units, power, control, instrumentation, telecommunication and data cables, April/2004.

[4] IEC 60092-359, Electrical installations in ships – Part 359: Sheathing materials for shipboard power and telecommunication cables, August/1999.

[5] IEC 60332-1-1, Tests on electric and optical fibre cables under fire conditions Part 1-1: Test for vertical

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flame propagation for a single insulated wire or cable Apparatus, July/2004

[6] IEC 60332-3-22, Tests on electric and optical fibre cables under fire conditions – Part 3-22: Test for vertical flame spread of vertically-mounted bunched wires or cables, February/2009

[7] IEC 60754-1, Test on Gases Evolved During Combustion of Materials from Cables - Part 1: Determination of the Amount of Halogen Acid Gas, January, 1994

[8] IEC 60754-2, Test on Gases Evolved During Combustion of Electric Cables; Part 2: Determination of Degree of Acidity of Gases Evolved During the Combustion of Materials Taken from Electric Cables by Measuring pH and Conductivity, July, 1991

[9] IEC 61034-1 , Measurement of Smoke Density of Cables Burning Under Defined Conditions - Part 1: Test Apparatus, April, 2005

[10] IEC 61034-2, Measurement of smoke density of cables burning under defined conditions – Part 2: Test procedure and requirements, April, 2005.

[11] IEC 60331-21, Tests for Electric Cables under Fire Conditions - Circuit Integrity - Part 21: Procedures and Requirements - Cables of Rated Voltage up to and Including 0,6/1,0 kV, April, 1999

[12] IEEE Std 1018, IEEE Recommended Practice for Specifying Electric Submersible Pump Cable – Ethylene-Propylene Rubber Insulation, September/2004.

[13] IEEE Std 1019, IEEE Recommended Practice for Specifying Electric Submersible Pump Cable – Polypropylene Insulation, September/2004.

VIII. VITA

Thiago Trezza Borges was born in Brazil in 1981.He

received the degree of Electrical Engineer in 2004 and the M.Sc. degree in 2006, both from the Federal University of Juiz de Fora (UFJF), Minas Gerais, Brazil and is currently a Ph.D. candidate in Electrical Engineering at the Graduate School of Engineering (COPPE) / Federal University of Rio de Janeiro (UFRJ).

Michael da Fonseca Pinheiro was born in Brazil 1981. He received the degree of Electrotechnical Technician in 1999 from the Federal Center for Technological Education (CEFET-RJ), Rio de Janeiro, Brazil.

Waldir de Melo Mota Junior was born in Brazil in 1972. He received the degree of Electrical Engineer in 1998 and the M.Sc. degree in 2010, both from the Fluminense Federal University (UFF), Rio de Janeiro, Brazil.