This work is a metallurgical analysis of the inner lining layer of pipeline used in welding process MIG C and MIG AF. The petrochemical industry, and others that use pipelines for transportation of their raw materials, faces a major challenge: how to increase the useful life of these products in a harsh environment work? In the specific case of the petrochemical industry, whom this research is directed, the pipes serve as means of transportation for oil and gas, products that are extremely aggressive to the internal walls of these tubes that are degraded by corrosion, caused mainly, by chemical composition, pressure and temperature these products. In this context the
welding of lining made with nickel-based alloys becomes an excellent option for the construction, repair and maintenance of equipment whose application be returned in harsh environments of work, allowing the improvement of characteristics required, such as the resistance to corrosion. It is this scenario that emerges the theme for this research, based on studies that indicate that the process of welding MIG / MAG with
the addition of cold wire, has to evaluate the metallurgical characteristics of the pipeline coating deposited by the derivative process MIG conventional – MIG-C and MIG with the addition of cold wire - MIG AF - using Nickel alloy ERNiCrMo-4 in carbon steel pipelines. The welds were deposited in pipes of 228.6 mm of diameter, forming a layer of internal lining of four passes, divided into three segments of the circumference of the duct, in three different welding energy: 1.1, 0.9 and 0.7 kJ / mm. These segments are removed specimens of the ducts, for the production of the samples. After metallography, performed on the samples, followed with the analysis
and characterization by optical microscope, scanning electron microscope and testing of microhardness. The coatings exhibited excellent surface quality for all operational packages used in obtaining the welds. The results of the analysis of the regions studied: metal base, partially mixed zone and heat affected zone, were compatible with the literature studied for both the MIG with the addition of cold wire, as for the conventional. In HAZ were observed values of Tungsten around 1.0%, the increased levels of hardness was credited to this fact. The microhardness results indicated that in both cases, MIG C and MIG AF, in 4 regions analyzed occurred
similarly, and the HAZ region which showed the highest values in the range 400-500 HV, while in the other regions range was between 250-350 HV. The results indicate that the process with cold wire, MIG AF, was as efficient as the conventional MIG C. The welding power increased the dilution of Fe in the weld metal. Precipitates rich in Mo and Cr were found in the weld metal.
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