Technical Presentations at the July 2007 Meeting
The presentation described 3 exposure studies: two in the USA and a third at Langstone Harbour, Portsmouth.
1984, 90-10 Cu-Ni (C70600) was installed for splash zone protection on the
legs of Stage 1 of the Morecambe Gas Field platforms in the Irish Sea.
This was the first major use of the alloy as a sheathing material and to
examine the performance of Cu-Ni in close detail, two studies were
initiated by the LaQue Center for Corrosion Technology in North Carolina,
first commenced in November 1983 with a series of 26 test pilings exposed
at Wrightsville Beach. Ten had Cu-Ni welded directly to steel, seven had
the sheathing insulated from the steel with concrete and seven were bare
steel. Some possessed cathodic protection and others did not. Two pilings
were clad with 65%Ni-Cu alloy 400(N04400) and cathodically protected.
Shortly afterwards, the programme was extended to include 14 pilings with
a layer of butyl rubber acting as insulator between the steel and Cu-Ni
sheathing. The pilings were systematically removed and examined over the
next ten years.
second set of trials began in 1987 and involved six pilings, slightly
offshore from the breaker line at Kure Beach fishing pier. Three were
positioned on the north side of the pier and three on the south. Each side
involved a plain steel control, Cu-Ni sheathing welded to the steel and
Cu-Ni sheathing insulated from the steel. All had cathodic protection
applied on the steel below the water line.
Both sites suffered the ravages of extreme weather including hurricanes to which the area is prone, but the piles survived. After 20 and 16 years exposure respectively, the test sites were abandoned and final long-term investigations carried out.
Wrightsville Beach Trails aimed to examine the viability of 90-10CuNi for
corrosion and biofouling protection in the splash, spray and tidal zones.
The test programme compared levels of fouling on electrically insulated vs
non insulated Cu-Ni sheathing, anode consumptions with and without
sheathing, corrosion rates of steel behind the sheathing and the sheathing
itself, galvanic attack at the top and bottom steel/sheathing junctions
when welded in position.
measurements of the depth of attack for the two year removals and
extensive sectioning and thickness measurements for the 5 and 10 year
removals were performed. The results indicated complete protection of the
steel behind the sheathing in the splash and spray zones. There was no
measurable loss of thickness of the Cu-Ni sheathing itself in the case of
the directly welded and insulated pilings. Post exposure measurements on
submerged areas of steel on the cathodically protected sheathed piles
showed that corrosion losses were comparable to those at the corresponding
areas on the cathodically protected bare steel controls. The mass of
biofouling accumulation on the sheathing that was electrically insulated
from the steel was 1-4% of that present on the bare steel after 10 years
exposure and low levels of fouling continued through 20 years. Pilings
with the directly welded sheathing accumulated less than 40% of the
biofouling mass compared to the bare steel controls.
sheathing also reduced the anode consumption rates particularly for 5 and
10 year removals. The most significant reduction was for the insulated
sheathing, presumably because the concrete reduced the area of metal
requiring cathodic protection. The anode consumption associated with the
directly welded sheathing was lower than for the bare steel and the
corresponding anode output was lower. This is considered to be due to the
favourable polarisation behaviour of the 90-10 Cu-Ni alloy. The potentials
indicated satisfactory levels of cathodic protection throughout the test.
at the sheathing/steel atmospheric junction eventually (15 years)
perforated the steel pipe in both the alloy 400 sheathed and direct welded
90-10 Cu-Ni sheathed pilings indicating it is important to maintain
coatings at the steel/sheathing interface at the top of the sheathing.
Cathodic protection will eliminate any galvanic effects at the bottom
interface although the data from these exposure results do not seem to
indicate that this is at all pronounced.
Kure Beach trials were less detailed and have produced more limited
results. The biofouling mass measurements were taken after 2 hurricanes
had damaged the pilings. However, they have served to reinforce the
general trends found in the Wrightsville Beach trials; namely, insulated
Cu-Ni sheathing provides the best resistance to biofouling and even
directly welded sheathing with cathodic protection on the steel can
achieve reduced fouling levels to bare steel pilings.
third trial initiated by the Nickel Institute involved an evaluation of
composite products involving 90-10 Cu-Ni. A
7 and 8 year raft exposure trial study in Langstone Harbour, UK, by
Portsmouth University evaluated the corrosion and biofouling behaviour of
adhesive backed foil and granules embedded in polychloroprene rubber.
Removals of panels for destructive assessment after 1,4 or 5 and 7 or 8
years were made. In addition, a third product under development at the
start of the study, involving expanded mesh with a neoprene backing, and a
single sample of hot rolled plate were included in this study.
results showed that all products showed restricted colonization of fouling
species and remained largely free of macro
fouling even though the Cu-Ni coverage varied between 30-100%. Where
present it could be wiped away fairly readily. The foil product had
thinned 5.5 μm per annum when averaged over a 7 year period.
[CDA Inc is acknowledged for the use of slides and information associated with the LaQue studies].
This presentation looked at corrosion
management, a problem for all ageing fleets.
It first highlighted the global opportunities and the massive costs
of corrosion. It then
considered a range of thin film corrosion sensors developed for platform applications.
The ATC have developed:
+ Elsyca N.V., Kranenberg 6, 1731 Zellik, Belgium,
++ Vrije Universiteit Brussel, Department IR\ETEC, Pleinlaan 2, 1050
presents a revolutionary 3D software tool for the design and optimisation
of cathodic protection systems for submerged and buried structures. It
provides the corrosion engineer an intelligent tool for managing
operational costs, significantly reducing expensive commissioning surveys
and costly repairs, adding major value to the cathodic protection
software is entirely CAD integrated, offering a user-friendly interface
for the CP design, including file import from numerous other CAD packages.
The key model features include amongst others: parameterisation of all
geometrical dimensions, simulation of 3D CP-configurations with arbitrary
complexity (including position and shape of ground beds, casings, ....),
interference from 3rd party CP-systems, ohmic drop effects in the
electrolyte, anodic and cathodic reaction polarization behaviour,
impressed current and sacrificial anodes, effect of cabling (ohmic
resistance along cable, effect of cable breakdown,
electrolyte resistivity, local metal dissolution based on Faradays law.
In this paper, the cathodic protection of a marine vessel (hull, shaft and propeller) using both impressed current and/or sacrificial anode systems will be investigated. Simulations will be compared with data available in literature. In a second step, numerical simulations will be performed in order to optimise the cathodic protection system.
Aims and background
Solid particle erosion and models
Flow corrosion and models
Combination of above Ή erosion-corrosion models
Not always bad when erosion + corrosion combine
Physical understanding of surface and sub-surface response
Mechanisms rarely considered
Aims of erosion-corrosion research
To understand wear-corrosion induced surface loss mechanisms to:
Inform surface selection
Improve life prediction
Optimise surface composition
Quantify wear-corrosion interaction factors (synergy)
Use electrochemical techniques:
Information on localised corrosion processes
of turbulent flow corrosion (mass transport and transverse momentum
erodent impacts effects
of passive films or inhibition/enhancement of film growth
Disturbance of charge in the double layer
of fresh reactive surfaces invoking area affects to
accelerate corrosion at these sites
Do we have any insight into erosion-corrosion?
Some for erosion and corrosion separately not much physical and electrochemical understanding of interactions (S) or applicable techniques to measure S also no robust data sets for modelling.
Erosion-corrosion must be better understood if component life is to be extended and generic models developed.
Surface films can reduce mechanical loss.
Simple analysis of electrochemical current noise is useful.
Need to know the current density of the affected or depassivated (i.e eroded) area for erosion system (material/environment).
Most identify mechanisms present.