Technical Presentations at the October 2008 Meeting

2.1   Keynote: ‘Prediction of the Service Life of Nickel-based Alloys A625 and A59 and Super Austenitic Stainless Steel B66 in Seawater Using In-house Crevice Corrosion Tests’, Anne-Marie Grolleau,  DCNS Cherbourg 

The successful use of Ni-based alloys and highly-alloyed stainless in seawater applications depends on their ability to resist localized corrosion and in particular crevice corrosion.  An extensive programme has been conducted in recent years by DCNS Cherbourg to optimise the use of such alloys for seawater pipings, identify their resistance to crevice corrosion and predict their performance under specific service conditions.  The paper described the in-house corrosion tests and methods used.  Results of an evaluation campaign performed on Ni-based alloys A625 (UNS N06625), A59 (UNS N06059) and super-austenitic stainless steel B66 (UNS S31266) were presented.  The paper also reviewed the influence of several factors which impact crevice corrosion initiation and propagation, such as crevice geometry, nature of gaskets, temperature, surfaces cleanliness and passivation treatments.  Anne-Marie Grolleau, Hervé Le Guyader, Valérie Debout. [Anne-Marie Grolleau, CETEC -DCNS Cherbourg, Code 0981 – Place BRUAT, BP 440 Cherbourg-Octeville]. 

Other relevant papers: 

‘Crevice Corrosion of Nickel Base Alloys and Highly Alloyed Stainless Steels in Sea Water’, H. Leguyader, V. Debout and A.M. Grolleau, DCN Cherbourg, Eurocorr 1999 - Aachen Germany. 

‘Crevice Corrosion Properties of Weld Overlays of Alloy 59 for Alloy 625 Flanges Repair’, H. Leguyader, V. Debout and A.M. Grolleau, DCN Cherbourg, Paper No. 33 - Eurocorr 2001- Riva Del Garda Italy. 

‘The Influence of Environmental Factors on the Crevice Corrosion of Alloy 625 in Natural Seawater’, F. Martin and P. Natishan, Naval Research Laboratory, Washington USA; A.M. Grolleau, DCN Cherbourg, Paper No. 02213 - NACE 2002 - Denver USA 

‘Ceramic Coating of Alloy 625 using Controlled Atmosphere Plasma Spraying for Sea Water Corrosion Protection’, V. Guipont. J.P Fauvarque, S. Beauvais, M. Jeandin (Ecole National Superieure des Mines de Paris, CNRS), H. Leguyader, H.Lepresle, AM Grolleau, (DCN Cherbourg), Thermal Spray 2003 USA 

‘Evaluation of Crevice Corrosion Properties of New Super-Austenitic Stainless Steel B66 in Natural Sea Water’, A.M Grolleau, H. Leguyader and V. Debout, DCN Cherbourg, Eurocorr 2006- Proceedings of WP 9 - Session H - Maastricht The Netherlands 

‘Crevice corrosion of Nickel Base alloys and Highly alloyed stainless steels in seawater’, H. Leguyader, V. Debout and AM Grolleau DCN Cherbourg, European Federation of Corrosion Publications No. 33 Marine Corrosion of Stainless Steels - Testing, Selection, Experience, Protection & Monitoring P226-243  

2.2  ‘NYB66 : Superaustenitic Stainless Steel : Mechanical and Corrosion Properties.  Development in Progress’, Anne Pascale Moiroux and Didier Laveze, Aubert et Duval 

Commonly used stainless steels and alloys have several drawbacks:

ü       Limited localised corrosion resistance in oxidising and sea water environments

ü       Structural instability in heavy section forgings

ü       High cost (Ni alloys)

There is a need for a steel with a better corrosion resistance but not too expensive: that’s why we promote the super-austenitic steel NYB66

NYB66 stainless steel has been developed for oil and gas and sea water applications.

It has been designed on the concept of super-austenitic stainless steels aiming for better corrosion resistance, better mechanical properties and better structural stability.

Several studies showed that NYB66 is a good compromise between corrosion resistance and mechanical properties. It shows better corrosion resistance in sea water, especially for crevice and pitting corrosion resistance than conventional super-austenitic, super-duplex, and even Ni base 625. Its mechanical properties are higher than other super-austenitic, and even higher than Ni base 625.

NYB66 microstructure is more stable than other 6 Mo super-austenitic stainless steels. It makes the steel suitable for high wall thickness components.

NYB66 steel is a serious candidate for corrosion applications in severe corrosion Medias.

[Anne-Pascale Moiroux, Aubert & Duval, 63770 Les Ancizes, France,  anne-pascale.moiroux-lemaire@eramet-aubertduval.com] 

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  4.1  Advances in On-Line Corrosion Monitoring in Industrial Plants’, Mark Mulvaney, Rohrback Cosasco Systems UK Ltd.  

Data communication networks installed in industrial plants and oil and gas installations, both off-shore and on shore, have provided an opportunity to extend the installation and reliability of on-line corrosion monitoring.  In order to provide the maximum benefit available from the use of such systems, significant advances in the design of corrosion monitoring instruments has been necessary.  This has involved the development of high resolution, (18 bit), digital transmitters and high resolution measuring probes, usable in virtually all environments, with immunity to interference by Iron Sulphide deposits.  By increasing resolution to ~ 1 x10-6 mm, corrosion rate changes of the order of 0.5 mpy (0.013mm/yr) can be detected within a few hours, allowing rapid response to corrosion upsets and process changes.  Distributed access via the internet allows instant access to the data at locations remote from the plant and the corrosion server.  New developments such as Wireless transmitters provide even more flexibility, both when installing new systems and extending existing networks. 

 4.2  An Introduction to IMO – PSPC Coating Specification for Ballast Tanks’, John Carter, Bodycote Testing Ltd

This presentation provided an overview of the IMO Coating Performance Standard for Water Ballast Tanks.  This Performance Standard for Protective Coatings (PSPC) provides the technical requirements for protective coatings in dedicated sea water ballast tanks of all types of ships of  500 gt and greater and double sided skin spaces on bulk carriers of 150m and greater in length.  

The Aims of the PSPC are:  

·         to provide a 15 year life for ballast tank coatings  over which it is defined as in being ‘good’ condition.

·         ‘Good’ condition is defined in resolution A.744(18) and is “ condition with only minor rust spotting”

·         Better coating systems with reduced maintenance

·         Improved safety at sea  

Further work is underway to develop a draft standard for:

·         Void spaces of all ships

·         Cargo tanks of oil tankers

·         Guidelines for maintenance and repair for protective coatings

·         Standards for protection of permanent means of access - not part of structural strength elements  

Main Elements of the PSPC:

·         Design of a specification and coating system

·         Coating System approval

·         Definition of inspection procedures

·         Production of a Coating Technical File (CTF) which records all aspects of the process

·         Verification of compliance  

IMO States: “ This Standard is based on specifications and requirements which intend to provide a target useful coating life of 15 years, which is considered to be the time period, from initial application, over which the coating system is intended to remain in “GOOD” condition. The actual useful life will vary, depending on numerous variables including actual conditions encountered in service”.

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