Underwater Electrochemical Offshore Tests of a Paint Coating Applied in Water on the Legs of an Oil Production Platform.

This paper presents the methodology developed for underwater measurements using electrochemical impedance spectroscopy (EIS) technique, aimed at determining the resistance of an epoxy coating applied in seawater to the legs of an oil production platform. Performing such underwater tests in an offshore environment was technically challenging. The results of measurements obtained on the platform were confronted with comparative results obtained in the laboratory, where the properties of the coating applied in water collected from the Baltic Sea (thickness, hardness, adhesion, and electrical resistance) were examined. This made it possible to conclude about the correctness of the paint coating application by divers on the legs of the platform. The single-layer epoxy coating applied by brush to the platform legs had a resistance above 10 kΩ∙cm2 and thus met the assumed minimum resistance of the protective coating cooperating with cathodic protection as the anti-corrosion protection system of the platform legs. The synergy of these two technologies ensures full protection of offshore structures against corrosion. Measurements of the potential of the platform legs confirmed this. Before painting, the potential value at a depth of 0-15 m was 310 ÷ 320 mV versus the zinc reference electrode, while after painting the potential value decreased to 220 ÷ 240 mV, which means that the effect of full cathodic protection was achieved and the platform legs were protected from corrosion. The developed methodology for underwater EIS measurements on the high seas can be applied to any underwater metal structure to assess the quality of protective coatings.

Corrosion Monitoring in Petroleum Installations-Practical Analysis of the Methods.

This paper presents the most typical corrosion mechanisms occurring in the petroleum industry. The methods of corrosion monitoring are described for particular corrosion mechanisms. The field and scope of the application of given corrosion-monitoring methods are provided in detail. The main advantages and disadvantages of particular methods are highlighted. Measurement difficulties and obstacles are identified and widely discussed based on actual results. Presented information will allow the corrosion personnel in refineries to extract more reliable data from corrosion-monitoring systems.

Investigation of the 0.4C-35Cr-45Ni-Nb Alloy after Service in High-Temperature Steam and Hydrocarbons Environment.

The paper presents the results of investigation of the 0.4C-35Cr-45Ni-Nb alloy, which operated in the cracked hydrocarbon feeds and dilution steam at 1125 °C. The material originated from the pyrolytic furnace coil tubes, of which internal walls were in contact with the aforementioned medium, whereas the external walls were in contact with the flue gases. The examination included metallographic and mechanical tests on the material after service exposure, the results of which were compared with the ones obtained for the as-received non-exposed specimens. The metallographic tests revealed changes in the alloy's structure manifested by formation of significant amount of the carbides due to carburization of the alloy from the steam and cracked hydrocarbon feeds side. The central and external parts of the alloy samples (having no contact with the process medium) underwent substantial degradation but within a relatively narrow zone of the material. The investigations of hydrogen and methane content in the alloy showed a high amount of these gases, resulting from high-temperature corrosion in steam environment. The mechanical tests demonstrated clear shortening of the plastic deformation range of the alloy due to penetration of the gases and formation of the carbides inside the material's structure. A low level of corrosion and no creep mechanism were detected.

The Effect of Increasing the Amount of Indium Alloying Material on the Efficiency of Sacrificial Aluminium Anodes.

Al-Zn-In alloys having 4.2% zinc content and various indium content in the range of 0.02-0.2% were tested with respect to the most important electrochemical properties of sacrificial anodes in a cathodic protection, i.e., the current capacity and potential of the operating anode. The distribution of In and Zn in the tested alloys was mapped by means of the EDX technique, which demonstrated that these elements dissolve well in the alloy matrix and are evenly distributed within it. The current capacity of such alloys was determined by means of the method of determining the mass loss during the dissolution by a current of known charge. The results obtained demonstrate that the current capacity of Al-Zn-In alloy decreases with the increase in the In content, which results in an increased consumption of anode material and shorter lifetime of anodes. With 0.02% In content, the capacity amounted to approx. 2500 Ah/kg, whereas the alloy with 0.2% In had as much as 30% lower capacity amounting to approx. 1750 Ah/kg. Microscopic examination for the morphology and surface profile of the samples after their exposure demonstrated that a higher indium content in the alloy results in a more uneven general corrosion pattern during the dissolution of such alloy, and the cavities (pits) appearing on the alloy surface are larger and deeper. As the indium content is increased from 0.02% to 0.05%, the Al-Zn-In alloy potential decreases by about 50 mV to -1100 mV vs. Ag/AgCl electrode, which is advantageous in terms of using this alloy as a sacrificial anode. When the indium content is further increased from 0.05% to 0.2%, the potential of the alloy is no longer changed to a more negative one. The results obtained from all these tests demonstrate that alloys containing up to 0.05% of In additive are practically applicable for cathodic protection.