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]
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.
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”.