Deep Water CP
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Deep Water CP
Addtime：2015-12-17 11:44:16 Print
Cathodic protection (CP) is widely applied for corrosion prevention on steel structures that are in contact with seawater. One of its most important applications is the protection of platforms and submerged structures.
Nowadays, gas and oil production is being developed in deeper waters (between 500m and 2,000m). Because maintenance becomes a difficult task at such depths, the reliability of the structure’s materials, the choice of optimal protection conditions, and the protection systems are very significant.
Several parameter affects the cathodic protection in the deep water, Hydrostatic pressure, Salinity, lower dissolved Oxygen, Low temperature, some of those affects described below.
Hydrostatic pressure affects the properties of seawater, and therefore, it could have possible effects on cathodic protection. Offshore CP systems can benefit from the development of calcareous deposits, which are known to depend on a number of main factors, such as dissolved oxygen content, temperature, salinity, pH, currents, and microbial films. Moreover, these factors interrelate with each other and with water depth, in a complex manner. However, there is further evidence that calcareous deposits do not always form in deeper, colder waters, and that when they do, the benefits they confer are variable. Lower dissolved oxygen content suggests both lower natural corrosion and lower cathodic current requirements. This is counterbalanced by high hydrostatic pressure effects on the activity of dissolved oxygen, by increasing the oxygen reduction current. CP systems for deep-water structures might need to be sized for greater mean-life current densities than their shallower counterparts. Lower temperatures, which increase the solubility of the calcareous compounds, contribute to this effect. All this is, in part, associated with the natural differences in seawater temperature and composition around the globe. When cathodic protection is applied, the protective current is the result of oxygen reduction and water reduction. The latter releases hydrogen atoms, which are absorbed on the metal surface. The hydrogen atoms can either recombine to hydrogen gas evolving from the surface, or get absorbed by the metal itself. Absorption of hydrogen can be detrimental for many high strength steels, as these will be susceptible to hydrogen embrittlement (HE) giving high probabilities of brittle failures. Hydrogen embrittlement of structural materials is of concern to the offshore oil industry. The effect of pressure on hydrogen embrittlement has been observed at low cathodic potential (-950mV/scE) for which hydrogen embrittlement shows a maximum efficiency (~), and at low pressure (300m equivalent depth).
In the previous：Offshore Platform & FPSONowadays, gas and oil production is being developed in deeper waters (between 500m and 2,000m). Because maintenance becomes a difficult task at such depths, the reliability of the structure’s materials, the choice of optimal protection conditions, and the protection systems are very significant.
Several parameter affects the cathodic protection in the deep water, Hydrostatic pressure, Salinity, lower dissolved Oxygen, Low temperature, some of those affects described below.
Hydrostatic pressure affects the properties of seawater, and therefore, it could have possible effects on cathodic protection. Offshore CP systems can benefit from the development of calcareous deposits, which are known to depend on a number of main factors, such as dissolved oxygen content, temperature, salinity, pH, currents, and microbial films. Moreover, these factors interrelate with each other and with water depth, in a complex manner. However, there is further evidence that calcareous deposits do not always form in deeper, colder waters, and that when they do, the benefits they confer are variable. Lower dissolved oxygen content suggests both lower natural corrosion and lower cathodic current requirements. This is counterbalanced by high hydrostatic pressure effects on the activity of dissolved oxygen, by increasing the oxygen reduction current. CP systems for deep-water structures might need to be sized for greater mean-life current densities than their shallower counterparts. Lower temperatures, which increase the solubility of the calcareous compounds, contribute to this effect. All this is, in part, associated with the natural differences in seawater temperature and composition around the globe. When cathodic protection is applied, the protective current is the result of oxygen reduction and water reduction. The latter releases hydrogen atoms, which are absorbed on the metal surface. The hydrogen atoms can either recombine to hydrogen gas evolving from the surface, or get absorbed by the metal itself. Absorption of hydrogen can be detrimental for many high strength steels, as these will be susceptible to hydrogen embrittlement (HE) giving high probabilities of brittle failures. Hydrogen embrittlement of structural materials is of concern to the offshore oil industry. The effect of pressure on hydrogen embrittlement has been observed at low cathodic potential (-950mV/scE) for which hydrogen embrittlement shows a maximum efficiency (~), and at low pressure (300m equivalent depth).
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