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Picture for Efficiency of Cathodic Protection of Stainless Steel in Confined Area - Further Understanding of the Protection Mechanism through Experimental Testing and Modeling
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Efficiency of Cathodic Protection of Stainless Steel in Confined Area - Further Understanding of the Protection Mechanism through Experimental Testing and Modeling

Product Number: 51324-20639-SG
Author: Charles Leballeur; Jean Vittonato; Nicolas Larché; Hervé Marchebois
Publication Date: 2024
$40.00
Cathodic protection (CP) of carbon steel has been extensively studied for structures exposed to the open sea. However, the knowledge and data available for carbon steel cannot be directly applied to stainless steels, especially in the case of confined surfaces that are prone to crevice corrosion. In the context of stainless steels, confined surfaces (such as the contact surfaces of fasteners or valves) are critical zones as crevice corrosion represents the primary failure mode for passive alloys in seawater. With CP, the local potential achieved in confinement areas is highly dependent on various factors, including the actual geometries (crevice gap, length, local pH and Dissolved Oxygen (DO), ohmic drops, etc.). These factors can raise questions about the actual efficiency of CP if the current cannot reach the confined area. Conversely, if sufficient current can reach the confined area, the risk of hydrogen embrittlement (especially for strain-hardened or precipitation hardened alloys) should be taken into consideration. A specific experimental setup has been constructed to characterize the electrochemical behavior of stainless steel in a confined environment and the physicochemical properties of the confined seawater. The results have shown a complete deaeration of the confined seawater under all test conditions, along with an increase of the pH when CP is applied. The tests have also highlighted the significant impact of slight crevice gap variation on the current distribution. Based on the experimental findings, polarization curves representing confined environments have been generated. These curves have been integrated into a finite element model, allowing for the extrapolation of the experimental results to different crevice geometries. After a few centimeters, little to no current should be able to reach the confined surfaces if the crevice gap is inferior to 10µm. However, the risk of corrosion of stainless steels remains limited due to the local CP-induced chemistry at the interface. The CP also mitigates the ohmic drop in the confined area which also tend to reduce the risk of crevice corrosion.
	Picture for Localized Corrosion Limit of Use of S13%Cr (UNS S41427) Connector in Converted Injection Treated Seawater Well
Available for download

Localized Corrosion Limit of Use of S13%Cr (UNS S41427) Connector in Converted Injection Treated Seawater Well

Product Number: 51324-20714-SG
Author: Nicolas Larché; Marianne Kleive; Charles Leballeur; Eva Malmanger
Publication Date: 2024
$40.00
Many systems can be converted and used for different applications not initially planned. This is the case for production wells, sometimes converted into water injection wells and for which the production tubing material selection is clearly not adapted for prolonged contact with natural seawater. Oxygen removal treatment must be applied but precise control is not obvious and excursions above zero or close-to-zero oxygen can occur. The production tubing material S13%Cr are known to be sensitive to dissolved oxygen excursions in seawater, but data from the literature cannot precisely help in defining the allowed limits of use. Exploring the possibility to convert a production well into a treated seawater injection well then requires a careful assessment of the corrosion resistance limits of the involved alloys. A series of corrosion tests in treated seawater were designed to assess the limits of use of fast connector made of alloy UNS S41427. The corrosion tests were performed both at laboratory scale and on full-scale fast connectors in a treated seawater flow loops simulating service conditions. For all the performed tests, maintaining the dissolved oxygen content (DOC) at 15 ppb and below never led to localized corrosion and has been considered as a safe condition in terms of corrosion risk for alloy S41427 at ambient temperature. It was found that prolonged dissolved oxygen content (DOC) above 30±10 ppb may lead to initial crevice corrosion after only 4 h of exposure. Globally, a very good correlation between the laboratory and the full-scale test results was found. The critical crevice potential for alloy S41427 was significantly affected by the cleaning process of the tested coupons, while the stop of the corrosion was always measured for potentials reached at DOC < 10 ppb. The proposed methodology, involving both laboratory and full-scale tests, allowed to precisely quantify the limits of use of UNS S41427 in treated injection well. It could be used for any other material and applications to help at designing adapted and reliable engineering diagrams for material selections.