Flaw Detection in the Deep-Rod Pump Cylinder after Ion Nitriding

Abstract

The article is devoted to evaluation of ion nitriding influence on possible deformation of deep-rod pump cylinders made of 38X2MUA steel tube blank. This article describes the analysis of the main flaws in the samples of deep-rod pump cylinders, obtained by cylinder surface hardening by means of plasma nitriding. Several samples of deep-rod pump cylinders of were selected, subjected to machining in accordance with technological process, chemical and heat treatment of the internal working diameter of cylinders by ion nitriding. Manufactured samples were subjected to instrumental control on Aerotest «Cylinder WGN-R»of actual parameters of the inner cylinder diameter to the required by design documentation. Further, sample witnesses were made from the cylinders to test nitrited layer hardness and to make metallographic analysis of the nitrited layer microstructure. The study revealed deviations in the shape and dimensions of the inner cylinder diameters, which were classified into two types: hoop and oval strains. Metalographic and hardness tests results showed deviation in surface hardness and deviation from the nitrited layer normal microstructure. The structure of the nitrited layer of the strained specimens has large surface nitride inclusions and a loose nitrited layer, regardless of the flaw type. Also, defective samples lack the required high-quality nitride area of higher hardness, to provide high corrosion and tribotechnical properties determining the life-span of the deep-rod pump cylinder. In this way, the main types of flaws arising at hardening of the internal cylinder working diameter have been identified and classified. The microstructure of the nitrited layer in the standard and defective samples is investigated and described. The correlation between nitrited layer structure flaws and geometrical parameters of the inner cylinder diameter have been determined.