Internal coating of pipes using the cathodic cage plasma nitriding technique

This work confirms the possibility of the application of a plasma nitriding technique, with a cathodic cage, for lining pipelines through the deposition of thin nitride films. The process using the cathodic cage technique is based on the simultaneous use of multiple hollow cathode effects. Thus, is possible to obtain a uniform lining promoving an increase in the hardness and corrosion resistance of treated samples, with elimination of edge and shadow effects in the nitrided layer. The cage is made of austenitic stainless steel AISI 316, containing a removable lid and holes with well defined diameters and distances between adjacent holes. Combining the tension and pressure in the process results in the possible occurrence of the hollow cathode effect in all holes. The material removed by sputtering is transferred to the workpiece surface. In this application, the cage in which a cathodic potential is applied is surrounded by the samples to be treated (glass tubes and 316 steel plate). The XRD analysis confirmed the deposition of iron nitrides in the presence of phases that are also seen in samples treated on the inside of the cage, which allows simultaneous treatment of internal and external samples in relation to the cage.