Erosion Wear Characteristics Of Several Plasma Spray Coatings

Gathering pipeline erosion is the most commonly seen failure in the petrochemical industry which is one of the hot issues urged to be alleviated in the process of gathering pipeline safe operation. Concerning the practical working condition of the gathering pipelines, the AT13, AT40, WC/Co, Ni60, Fe313 and n-AT13 were coated on the surface of 20# steel with plasma spraying technique. Scanning electron microscopy and X-ray diffraction were used to observe and analyze the micro structure of the coatings. The vacuum impregnation liquid method, dual sample stretching method, microhardness testing method and the indentation method were used to test and analyze the porosity, adhesive strength, microhardness and fracture toughness of the coatings respectively. Then the airflow with sand jet method was used to test and analyze the erosion resistance of the coatings. The effects of erosion environment parameters and coating properties on the erosion resistance of the coatings were studied. Through observing and analyzing the morphologies of erosion coatings, the erosion characteristics of the coatings were discussed.The results showed that:among the six kinds of coating produced by plasma spray, lamellar structure had been observed obviously in the AT13, AT40, WC/Co, Ni60 and Fe313 coating,but lamellar structure in the n-AT13 coating had not been observed obviously. There were amounts of pores and cracks in the same direction of the coating layer superimposed existed in the coatings. Additionally, the coating and substrate was connected by mechanical riveting. The coatings with the least and biggest porosity were that of WC/Co coating and Fe313 coating, and their modulus were 5.9% and 7.8% respectively. The coatings with the highest and lowest adhesive strength were that of n-AT13 coating and Fe313 coating, and their modulus were 31.8MPa and 17.9 MPa respectively. The coatings with the highest and lowest average microhardness were that of n-AT13 coating and Fe313 coating, and their modulus were 1028.81 and 582.66 respectively. The coatings with the highest and lowest fracture toughness were that of n-AT13 coating and AT 13 coating, and their modulus were 5.896J/m2 and 4.816J/m2 respectively.Erosion wear test showed that:the erosion wear resistance of six kinds of coating were better than that of 20# steel. The mass loss of these six kinds of coating achieved the top at the angle of 90°. At the angle of 30°, the ranking of the mass loss of the coatings was n-AT13< AT13<WC/Co<AT40<Ni60<Fe313. The mass loss of the n-AT13 coating was 3/4 times of that of the AT 13 coating, and the mass loss of the AT 13 coating was 2/3 times of that of the Fe313 coating. At the angle of 90°, the ranking of the mass loss of the coatings was n-AT13< WC/Co<AT40<AT13<Ni60<Fe313. The mass loss of the n-AT13 coating was 3/4 times of that of the WC/Co coating, and the mass loss of the WC/Co coating was 3/4 times of that of the Fe313 coating. At diffrent angle, with the increase of erosion time, no incubation periodthe was seen. The transitional stage was the first 1-4min. The transitional stage time and the surface quality of coatings and erosion angle had a certain correlation. At diffrent angle, with the increase of particle velocity, the mass loss of six kinds of coating were dramatically increased. Clearly, the hardness of the coatings was not the single factor influenced on the erosion wear resistance of the coating.Observation and analysis of morphology of the erosion coating showed that:at the angle of 30°, the erosion wear of the coatings exhibited one or more features such as microscopic cutting, microscopic fatigue spalling and particles shedding. At the angle of 90°, the erosion wear of the coatings mainly exhibited fatigue spalling feature. In conclusion, the erosion failure mechanism of the coatings was mainly exfoliated.Concerning the practical working condition of the gathering pipelines and the characteristics of the erosion wear resistance of the coatings, WC/Co coating can be used as the anti-erosion protective coating on the gathering pipelines, especially when applied at high erosion angle. AT13 coating can be used as the anti-low-angle erosion protective coating on the gathering pipelines.