Sour Environmental Severity for HIC Susceptibility

The severity of sour environments has been determined in accordance with the European Federation of Corrosion 16 and NACE MR0175/ISO 15156-2:2015 standards for carbon and low-alloy steels, based on the experimental results of sulfide stress cracking (SSC). However, the severity map obtained from SSC test results cannot be applicable to the hydrogen-induced cracking (HIC) susceptibility. In this study, the hydrogen permeability and crack area ratio (CAR) of HIC under various pH and H2S partial pressures (pH2S) were measured to establish the link between the sour environmental severity and HIC susceptibility using grades X65 to X80 linepipe steels. In addition, the hydrogen concentration at the location of the HIC was calculated by the finite element analysis. The results showed that the sour environmental severity map obtained from hydrogen permeation tests changes with time, because the hydrogen permeability reached maximum values in the early stage and steady-state values in the later stage. Then, the HIC susceptibility did not correspond to the maximum permeability, but to the steady-state hydrogen permeability. In addition, the hydrogen content at the location of the HIC did not correspond to the maximum hydrogen permeability but corresponded to the steady-state hydrogen permeability, because HIC occurred in the center segregation part and the hydrogen atoms required a certain time to diffuse from the metal surface to the mid-thickness. These results suggest that the HIC susceptibility is dominated by the severity map obtained from the steady-state hydrogen permeability.

COMUNIDADES DE ESPONJAS DE LOS ARRECIFES DEL ARCHIPIÉLAGO SABANA-CAMAGÜEY, CUBA

The research was carried out in order to know the sponge community composition and structure of the Archipelago Sabana-Camagüey, and to assay their use as indicators of the environmental severity and predictability, as well as of the most important stressors of this territory. For this purpose, sampling was done at stations located in 10 reef transects (between 10 and 20 m deep). Species which occurred more frequently with numerical dominance are typical of environments submitted to strong sedimentation and turbulence, which suggests that these environmental stressors and light are the main determinants of sponge community structure and composition in the studied reefs. The development of dense algal mats is also determinant in shallow stations. Species heterogeneity and species richness, and density tended to be higher toward deeper stations, which indicates an increase of environmental favorability for sponges with depth. Equitability tended to be more homogeneous across the studied depth range. Its values were generally high, which suggests relatively constant environments for sponges. Heterogeneity index was more frequently influenced by equitabiliy than by species richness. For that reason, a greater influence of environmental stability than environmental favorability on the high values of this index in the studied reefs is suggested. By means of a meta-analysis process, the position of the values of some indexes within their universe of variation was analyzed. At more than 10 m in depth diversity indexes tended to be relatively higher than in other Cuban reefs. Also by applying meta-analysis, stations were classified within a bidimensional gradient of environmental severity and environmental predictability. Univariate indexes and the dominant species, complemented with species dependent multivariate methods permit to infer the most important stressors, and environmental severity and predictability.