Technical Presentations at the April 2006 Meeting
ultrasonic technology has progressed greatly since TWI introduced the
first commercial instrument, Teletest®, for detecting corrosion in pipe
over 10 years ago. However, much research is still needed if the
technology is to progress from being a screening tool to one that can
assess the extent, depth and nature of corrosion as well as reliably
A test programme was conducted to study the corrosion behaviour of a range of steels and CRAs in low oxygen content (20 & 200 ppb) seawater. The test materials ranged from carbon and low alloy steels through austenitic, martensitic and duplex stainless steels to nickel-based Alloy 718. Seawater injection conditions were simulated in tests conducted in the above conditions at 30ºC. Commingled water (a mixture of produced water and injected seawater) was simulated by adding carbon dioxide to these test environments and testing at 60ºC. High oxygen levels were injected periodically to simulate the effects of poorly controlled seawater deaeration. Tests were conducted in static and flowing conditions.
The results show the sensitivity of these materials to the dissolved oxygen content of injection and commingled waters. Pitting, crevice and under-deposit corrosion occurred to varying degrees enabling guidelines to be developed for material selection in this area.
This work was sponsored by T. N. Evans (BP) & P. I. Nice (Statoil).‘X-ray Tomography Techniques for Localised Corrosion and Environmentally Assisted Cracking Studies’, Brian Connolly (Birmingham University)
experiments in aqueous salt solution utilising high-resolution (0.7 mm)
synchrotron X-ray tomography have been performed to investigate the
propagation of intergranular corrosion (IGC) within an aluminium airframe
alloy. These observations will be used to quantify growth rates for
this three dimensional phenomenon as a function of the differing
metallurgy found in the various regions of a AA2024-T351 friction stir
weldment as well as a function of applied remote stress in a AA2024-T8
temper used to simulate the electrochemical reactivity of a weld heat
evolution of IGC in aluminium alloys is a problem of fundamental interest
to the corrosion community, and is poorly understood. Accurate IGC
rates are difficult if not impossible to quantify using conventional 2D
measuring methods. Of particular interest is the determination of
how IGC propagates from localised corrosion sites such as pits associated
with large (3-10 mm) intermetallic constituent particles.
Furthermore, it is important to assess how the presence of a remote stress
affects the propagation of intergranular attack.
tomography scans have been carried out on individual specimens at
incremental corrosion exposure times to determine the time-dependence of
the 3D propagation of IGC through the microstructure. These
experiments show the progressive development of localised corrosion sites
within the bulk of the sample and quantify the mode and rate of attack for
different microstructural regions and applied stress state.
analysis of this work will make a significant contribution to the effort
to elucidate the controlling electrochemical/physical mechanisms dictating
the development of localized corrosion sites, specifically, the
propagation of IGC and possible transitions to stress corrosion cracking.
Clearly defining the evolution of the localized corrosion morphology as
well as quantifying its growth rate will provide valuable underpinning
scientific knowledge that will significantly contribute to the on-going
modelling effort for life prediction of aircraft components.
Connolly,a, [email protected],
S.J. Fox,a, D.A. Horner,a, S. Ghosh,a, A.J. Davenport,a, C. Padovani,a, M.
Preuss,b, N.P. Stevens,b, T.J. Marrow,b, J. -Y. Buffiere,c, E. Boller,d,
M. Stampanoni,e, and A. Grosoe
Metallurgy and Materials, University of Birmingham, United Kingdom, b.
School of Materials, University of Manchester, United Kingdom, c. GEMPPM
INSA, Lyon, France, d. European Synchrotron Radiation Facility, Grenoble,
France, e. Swiss Light Source, Paul Scherrer Institut, Switzerland]
developed following a request by the European oil industry for a weldable,
high strength, durable, corrosion-resistant castable steel alloy. The
target was a material with a proof strength of greater than 415N/mm2
along with a resistance over a wide range of temperatures to various
complex media such as sour/sweet gases, acids, alkalines, aerated sea
water and their combinations. Vistar exceeds these criteria and has passed
every test made of it to date by a considerable margin. In 2001 Vistar was
accepted in the industry by being awarded a UNS grade number (J95370) and
has been approved by NACE. It is the only castable high strength super
austenitic stainless steel on both the UNS & NACE accredited lists and
is also included in ISO 15156 part 3.
unusually, includes a high proportion of low atomic mass elements.
Together with the finely balanced ratios of each of its other component
elements these elements create an extremely dense austenitic structure and
prevent the formation of intermetallic phases. The low atomic mass
elements create an electron relationship of full orbitals within the face
centred cubic lattice. This closely packed structure prevents “shear”
and “slip”, and minimises dislocation mobility, achieving extreme
levels of corrosion resistance and exceptional strength for an austenitic.
testing to determine the level of Vistar’s corrosion resistance was
performed by Bodycote Material Testing under the close observation of Dr
Chris Fowler. Following the testing Dr Fowler confirmed that no signs of
pitting, crevicing or cracking had occurred. The material demonstrates
high resistance to sour chloride environments and has passed all the tests
to NACE MRO175.
In conclusion the testing performed to date demonstrates that Vistar has performed better than all the austenitics that it has been tested against, as well as matching, and in some places out-performing, the titanium products used.