Abstract:In the oil and gas industry, the manufacture of equipment using materials that resist aggressive media is one of the greatest challenges. UNS S31803 duplex stainless steel is widely used for this purpose owing to its good combination of mechanical and corrosion resistance. The objective of this work was to evaluate the effect of induction solution heat treatment using autogenous TIG welding on UNS S31803 DSS sheets. Sheet samples were subjected to two different treatment parameters for a duration of 10 s and at temperatures of 1050 and 1150 C. The results obtained with the treatments were compared with those of the as-welded condition, which was the reference condition. Quantitative and qualitative analyses of the samples were carried out, in addition to microstructural characterization using confocal microscopy and a corrosion resistance study as per ASTM G48 standard. We observed that the best results were obtained with a treatment of 10 s at 1150 C, which was able to eliminate chromium nitrides and re-establish the proper balance of the ferrite and austenite phases. In addition, the treatment was able to reduce hardness and provide welds free of cracks and discontinuities, also presenting a low corrosion rate.Keywords: duplex stainless steel; welding; corrosion; solution heat treatment
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Oxygen (O2). It is the only impurity which is absent in natural gas reserves. Usually onshore and offshore lines of gas wells are connected to larger lines that bring gas to the plant. Sometimes gas collection systems operate under atmospheric pressure. As a result of leakage and opening valves, air can enter the system and cause corrosion. The appearance of oxygen corrosion is pitting. In addition to corrosion, oxygen at concentrations > 50 ppmv can oxidize amines and glycols at appropriate units with formation corrosive substances, to influence inhibitor efficiency, to react with hydrocarbons during regeneration at high-temperature adsorption bed with water formation, to influence resistance of stainless steels to chloride SCC (Stress Corrosion Cracking), and galvanic corrosion. It is recommended not exceed oxygen concentration in natural gas above 10 ppmv. Oxygen causes corrosion of carbon steel and low-alloy steels, copper and its allloys. However, oxygen is required to keep protective oxide films on stainless steels, titanium, and aluminum. Philosophy of prevention from oxygen attack is to keep systems free of oxygen gas. There are the following methods of preventing oxygen penetration into natural gas systems, its removal and prevention from oxygen attack: maintenance of gaskets, rings, valves, pumps, compressors and other equipment and areas where the air can enter; keep positive pressure (above atmospheric pressure); blanketing with inert gas (e.g., nitrogen) above the surface of liquids in tanks; use of oxygen scavengers at low oxygen concentrations or catalytic reaction at high its quantities; deaeration; and use of coatings. 2ff7e9595c