technical product information cathodic … constant a and b for calculation of paint coatings...

Technical Product Information CATHODIC PROTECTION

Sacrificial Anode Systems

Sacrificial Anode for WILSON WALTON INTERNATIONAL® (ES) Offshore Application

ALOLINE® BA-778 S Equivalent to NORSOK-M503 & GALVALUM III

Sacrificial Anodes for WILSON WALTON INTERNATIONAL® (ES) Offshore Application

0713COMOFFSZNAL © 2013Wilson Walton International® (ES), S.A. • All rights reserved

Introduction Wilson Walton International® undertakes a wide variety associated with the British Offshore oil gas industries including large fabrication work at our main works on Teesside as well on platforms and rigs overseas.

If it is connected with offshore engineering then Wilson Walton International® is likely to be involved – Jackets, Modules, Floating Production Systems, Conductor Pipe Installations, Electrical Installation and Mechanical Outfitting – all are part of the comprehensive service Wilson Walton International® (ES) offers the offshore industry.

The sacrificial anode method of cathodic protection has been used to combat corrosion of metals by sea water for over 150 years. Wilson Walton International® leads in the development of sacrificial anode system for use in offshore applications and has modern foundry facilities in the around the world, all manufacturing to the same exacting quality control procedures.

The Aloline® and Zincoline® range of alloys are widely accepted for offshore use and alloy designations are common throughout the WWI® Group. Wilson Walton International® experts will advise on the most appropriate alloy for any given application and offer a full system design service if required, together with commissioning, testing and monitoring services.

Alloys Wilson Walton International® Group has developed in conjunction with British Aluminum (BACO) the BA 778 S Aloline® aluminium alloys and is equivalent to GALVALUM III & NOSRSOK M503, over a long period during which their excellent performance characteristics have been widely recognised. Evidence of this can be found in the number of Aloline® based systems installed on North Sea offshore structures.

Aloline® is protected by worldwide patents and is characterized by:

• light weight • high electrical capacity – 2700 ampere hours per kilogram • high solution potential – 1100 mV negative to a Ag/AgCI seawater

reference cell • even corrosion pattern without fissuring • stability of composition and performance during storage and service

These features allow substantial savings to be made, both in the cost of materials and in the cost of installing cathodic protection systems using anodes cast in Aloline® aluminium alloy.

The ALOLINE® of alloys based on Aluminium‐Zinc with an Indium activator and Zinc alloys are manufactured under the trade name ZINCOLINE®

Wilson Walton International®´s standard range of alloys is detailed in the table below. Other alloy formulations or modifications to the standard alloys, eg in respect of limits on residual elements such as Iron, can be manufactured to customer specification.

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0713COMOFFSZNAL ©2013Wilson Walton International® (ES), S.A. • All rights reserved

Composition Aloline® BA 778 S

Zincoline® US Military

Zinc 3.5 – 5.0 Balance

Aluminium Balance 0.1 – 0.5

Copper 0.005 max. 0.005 max.

Silicon 0.06 max. ‐

Iron 0.15 max. 0.005 max.

Titanium ‐ ‐

Bismuth ‐ ‐

Indium 0.015 – 0.04 ‐

Lead ‐ 0.006 max.

Cadmium ‐ 0.025 – 0.07

Nominal Electromechanical Capacity (AH/Kg) 2700 780

Nominal Solution Potential (mV) ‐1100 ‐1050

Density (Kg/m3) 2710 7000

Applications ALOLINE®, BA 778 S

Originally developed in conjunction with British Aluminium (BACO) to replace magnesium containing alloys for protection of crude carrier cargo/ballast tanks, this alloy has proved extremely suitable for offshore applications and operates even at low anode current densities and elevated temperatures. Aloline® BA 778 S is therefore recommended for use on buried pipeline, coated sub‐sea structure, semi‐submersible hulls, offshore jackets and general piled structure.

ZINCOLINE® Zinc alloys based on US Military A 18001 specifications are suitable for general sea water applications but their high specific gravity and low electrochemical capacity makes them less favoured for use on jackets and the structures. Zinc alloys operate over very wide range of anode current densities and in higher resistivity waters and saline mud, but are not suitable for use at temperatures about 50ºC. Zincoline® is therefore recommended for use on coated structures where weight is of less consideration and for buried sub‐sea pipelines at ambient operating temperatures.

Anode Types Sacrificial anodes types for offshore structures or pipelines are many and varied. Structural anodes may be flush mounted with flat bar steel inserts or may be “Stand Off” types generally with tubular steel inserts which may be reinforced with concentric or long elbow reducers to meet structural design requirements for a given anode location. Pipeline anodes in bracelet form may be in paired “half‐shells” or segment anode assemblies. Bracelet anodes may be squared ended or tapered and with a variety of fixing arrangements incorporated into the insert design.

Anodes are cast around steel inserts or cores which support the anode material, permit attachment to the structure or pipeline and provided an electrically continuous path from structure to anode surface. Some of the various anode/insert configurations available are indicated below and Wilson Walton International®´s experts can advise on the most appropriate anode type for any specific application.

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rof sedonA laicifircaS WILSON WALTON INTERNATIONAL® (ES) Offshore Application


System Design The design of a cathodic protection system for offshore structures will depend on many factors such as geographical location, environmental conditions, exposed surface areas, complexity of structural members, coating quality, etc and a well engineered system will take into account all the relevant factors during detailed design. Additionally, there may be specific Class Society Authority requirements to be met.

The final design should result in anodes of the optimum net weight for design life with the necessary current output at all stages of anode consumption to meet the expected current demand. The quantity and location anode should ensure a uniform cathodic potential at all points on the structure’s surface throughout its design life although for some structures anodes may be retrofitted.

Wilson Walton International® (ES) engineers can advise on any aspect of detailed design for offshore sacrificial anode applications. Additionally there are a number of published design guides for offshore cathodic protection and some of the more relevant design parameters are detailed in the following sections.

Wilson Walton International® (ES) uses the most demanding international standards such as DNV-RP-B401/101/F103 & NORSOK 503/505/506/501/N-001.

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Design Data Current Densities (A/m2) Minimum design current densities for protection of bare metal surface, as a function of “depth and

climatic regions” based on surface water temperature (DNV‐RP‐B401; page 30)

Tropical (> 20ºC)

Sub‐Tropical (12 – 20ºC)

Temperate (7 – 11ºC)

Arctic (< 7ºC)

Depth (m)

Initial Mean Final Initial Mean Final Initial Mean Final Initial Mean Final

0 ‐ 30 0.15 0.07 0.10 0.17 0.08 0.11 0.20 0.10 0.13 0.25 0.12 0.17

>30 ‐ 100

0.12 0.06 0.08 0.14 0.07 0.09 0.17 0.08 0.11 0.20 0.10 0.13

>100 – 300

0.14 0.07 0.09 0.16 0.08 0.11 0.19 0.09 0.14 0.22 0.11 0.17

>300 0.18 0.09 0.13 0.20 0.10 0.15 0.22 0.11 0.17 0.22 0.11 0.17

Minimum design current densities for protection of reinforcement steel (i.e. in concrete structure), as a function of “depth and climatic regions” based on surface water temperature (DNV‐RP‐B401; page 30)

Tropical (> 20ºC)

Sub‐Tropical (12 – 20ºC)

Temperate (7 – 11ºC)

Arctic (< 7ºC)

Depth (m)

Initial Mean Final Initial Mean Final Initial Mean Final Initial Mean Final

0 ‐ 30 0.0025 0.0015 0.0010 0.0008

>30 ‐ 100

0.0020 0.0010 0.0008 0.0006

>100 0.0010 0.0008 0.0006 0.0006

Recommended constant a and b for calculation of paint coatings breakdown factors. (DNV‐RP‐B401; page 30)

Recommended a and b values for Coating Categories I, II and III Depth (m) I

(a = 0.10) II

(a = 0.05) III

(a = 0.02)

0 ‐ 30 b = 0.10 b = 0.025 b = 0.012

>30 b = 0.05 b = 0.015 b = 0.008

Sea water resistivity as a function of temperature for salinity 35 %. (DNV‐RP‐B401; page 32)

Location Typical Resistivity (Ohm·m) Approx.

Tropical Seas (25ºC) 18

North Sea (<10ºC) 27

North Sea mud 60 – 75

North Sea clay 75 – 110

North Sea sand/stiff clay 110 ‐ 160

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The information shown on this publication is confidential and must not be copied nor conveyed to third parties without the express permission of Wilson Walton International® (ES), S.A. Our continuing commitment to quality products may mean a change in specification without notice. 1ª edi.1972 ‐ Rev01. 09/13 ©2013Wilson Walton International® (ES), S.A. • Printed in Spain • All rights reserved • Vo. IN

This publication is one of a series of Technical Product Information brochures on aspects of cathodic protection for offshore, landbased and marine applications. Further information about the series is available on request.

Certain items shown on this publication are subject to worldwide patent applications.

Esta publicación forma parte de una serie de folletos de información técnica de productos relacionados con la protección catódica para aplicaciones offshore, landbased y marina. Para más información envíenos su petición.

Algunos de los artículos que aparecen en esta publicación están patentados por todo el mundo.

WILSON WALTON INTERNATIONAL®

The Wilson Walton International® group incorporates companies established in the principal shipping centres of the world. This structure facilitates international manufacture of the Wilson Walton International® product range and the availability of local expertise and system design. The WWI® organisation is service orientated and geared primarily to the marine, offshore & landbased market..

El grupo Wilson Walton International® incorpora al grupo aquellas empresas situadas en los principales centros marítimos del mundo. Esta estructura facilita la fabricación internacional de la gama de productos de Wilson Walton International® y la disponibilidad de los conocimientos locales y el diseño de los sistemas. La organización de Wilson Walton International® está orientada al servicio y dirigida principalmente al mercado marítimo, offshore y landbased.

SYSTEMS & PRODUCTS (Marine, Port Facility, Land Based & Offshore Applications)

Sacrificial Anode Systems. ALOLINE® & ZINCOLINE® Impressed Current Systems. (ICCP) AQUAMATIC® systems for the protection of ships hulls and marine growth prevention system (MGPS) PRAICOMATIC® for sea water circuits. ALOLINE®, FERROLINE® & CUPROLINE®.

Wilson Walton International® (ES), S.A. Crta. de FUENCARRAL, 44 - EDIF. 9 - LOFT 19

Tlf.: +34 91 616 44 43 – 45 59 Fax: +34 91 616 53 01 28108 – ALCOBENDAS - (MADRID) - SPAIN [email protected] www.wilsonwaltoninternational.es

Your Local Wilson Walton International Agent/Office is / Agente Local de Wilson Walton International® (ES):

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technical product information cathodic … constant a and b for calculation of paint coatings...

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