Monitoring corrosion under insulation utilising electrochemical testing.

This paper proposes a novel sensor-based instrumented monitoring system for the specific detection of corrosion at the CUI interface. Electrochemical Testing (ET), Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were all used to gather, process and validate the sensor output. A comprehensive literature review was firstly completed to understand the current industrial and research practises. The experimental methodology featured an experiment using a stainless-steel wire mesh at the CUI interface. The experiment compared the behaviour between four samples without the mesh and four with the stainless-steel wire mesh at the CUI interface, in order to monitor any corrosive activity. The mesh was found to be useful in measuring key parameters such as; cell impedance, scale resistance, coating capacitance, charge transfer resistance and the total cell resistance and capacitance. SEM and EDS were used once the experiment had reached the end of its duration. Both methods provided information about the corrosion products and mechanisms at the interface validating the findings of the electrochemical investigation. Certain limitations of the mesh were identified such as its willingness to corrode and limited lifespan. However, it was concluded that the mesh was a valuable method for extracting key information about the condition of the CUI interface

Factors influencing magmatism during continental breakup: New insights from a wide-angle seismic experiment across the conjugate Seychelles-Indian margins

We present a model of the northern Seychelles continental margin derived from controlled source, wide-angle seismic traveltime inversion and teleseismic receiver functions. This margin has been widely cited as a classic example of rifting in association with a continental flood basalt province, the Deccan Traps. However, we do not find the typical set of geophysical characteristics reported at other margins linked to continental flood basalts, such as those of the north Atlantic. The oceanic crust formed immediately after breakup and throughout the first 3 Ma of seafloor spreading is just 5.2 km thick, less than half that typically seen at other volcanic margins. The continent-ocean transition zone is narrow and while two packages of seaward-dipping reflectors are imaged within this transition they are weakly developed. Beneath the thinned continental crust there is an approximately 4 km thick layer of high-velocity material (7.5–7.8 km/s) that we interpret as mafic material intruded and underplating the lower crust. However, we believe that this underplating most likely happened prior to the breakup. Overall the observations show that the rifting of India from the Seychelles was characterized by modest magmatism. The spatial extent of the Deccan flood basalt province is therefore smaller than previously thought. We speculate that either the lateral flow of Deccan-related hot material beneath the breakup region was hampered, perhaps as the rifted margins did not intersect the center of the Deccan source, or there was incomplete melt extraction from the wide melting region that formed between the rapidly diverging plates. If the latter explanation is correct, then the rate of plate separation, as indicated by the initial seafloor-spreading rate, is more important in controlling the volume of magmatism generated during continental rifting than has been previously recognized

Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada

We present a compressional seismic velocity profile of the crust of the eastern margin of the Grand Banks of Newfoundland, Canada. This velocity model was obtained by a tomographic inversion of wide-angle data recorded on a linear array of 24 ocean bottom seismometers (OBSs). At the landward side, we imaged a crustal thickness of 27 km in Flemish Pass and beneath Beothuk Knoll, which is thinner than the 35-km-thick crust of the central Grand Banks. We therefore assume that the eastern rim of the Grand Banks stretched uniformly by 25%. Farther seaward, the continental crust tapers rapidly beneath the continental slope to ?6 km thickness. In the distal margin we find a 60-km-wide zone with seismic velocities between 5.0 and 6.5 km s?1 that thins to the southeast from 6 to 2 km, which we interpret as highly extended continental crust. Contrary to other seismic studies of the margins of the Grand Banks, we find seismic velocities of 8 km s?1 and higher beneath this thin crustal layer in the continent-ocean transition. We conclude that mantle was locally emplaced at shallow levels without significant hydration from seawater or serpentinized mantle was removed along a décollement in the final stages of continental rifting. The outer edge of highly extended continental crust borders a 25-km-wide zone where seismic velocities increase gradually from 6.3 km s?1 just below the top of acoustic basement to 7.7 km s?1 at 5 km below basement. We interpret this area as a relatively narrow zone of exhumed and serpentinized continental mantle. Seaward, we imaged a thin and laterally heterogeneous layer with a seismic velocity that increases sharply from 5.0 km s?1 in basement ridges to 7.0 km s?1 at its base, overlying mantle velocities between 7.8 and 8.2 km s?1. We interpret this area as unroofed mantle and very thin oceanic crust that formed at an incipient, magma-starved, ultraslow spreading ridge. A comparison of the conjugate rifted margins of the eastern Grand Banks and the Iberia Abyssal Plain show that they exhibit a similar seaward progression from continental crust to mantle to oceanic crust. This indicates that before continental breakup, rifting exhumed progressively deeper sections of the continental lithosphere on both conjugate margins. A comparison between the continent-ocean transition of the Grand Banks and Flemish Cap shows that the final phase of continental rifting and the formation of the first oceanic crust required more time at the Grand Banks margin than at the southeastern margin of Flemish Cap

Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data on the Newfoundland nonvolcanic margin

Prestack depth migrations of seismic reflection data collected around the Ocean Drilling Program (ODP) Leg 210 transect on the Newfoundland nonvolcanic margin delineate three domains: (1) extended continental crust, (2) transitional basement, and (3) apparent slow spreading oceanic basement beyond anomaly M3 and indicate first-order differences between this margin and its well-studied conjugate, the Iberia margin. Extended continental crust thins abruptly with few observed faults, in stark contrast with the system of seaward dipping normal faults and detachments imaged within continental crust off Iberia. Transition zone basement typically appears featureless in seismic reflection profiles, but where its character can be discerned, it does not resemble most images of exhumed peridotite off Iberia. Seismic observations allow three explanations for transitional basement: (1) slow spreading oceanic basement produced by unstable early seafloor spreading, (2) exhumed, serpentinized mantle with different properties from that off Iberia, and (3) thinned continental crust, likely emplaced by one or more detachment or rolling-hinge faults. Although we cannot definitively discriminate between these possibilities, seismic reflection profiles together with coincident wide-angle seismic refraction data tentatively suggest that the majority of transitional basement is thinned continental crust emplaced during the late stages of rifting. Finally, seismic profiles image abundant faults and significant basement topography in apparent oceanic basement. These observations, together with magnetic anomaly interpretations and the recovery of mantle peridotites at ODP Site 1277, appear to be best explained by the interplay of extension and magmatism during the transition from nonvolcanic rifting to a slow spreading oceanic accretion system