Xueqian Cao

In order to solve the problem of the corrosion and wear of N80 metal pipelines exposed to corrosive media and abrasive sand during the development of petroleum resources, the proposed solution involves utilizing HC-PECVD technology to deposit a series of multilayer Si-DLC films with varying thicknesses on the inner surfaces of the N80 steel pipes. This investigation systematically explored the microstructure, mechanical properties, tribological features, and corrosion resistance of the multilayer Si-DLC films. Remarkably, after coating the multilayer (Si-DLC)₄₀ film on the inner wall of the N80 tube, the friction coefficient decreased from 0.7~0.75 to 0.2~3, and the wear rate decreased by two orders of magnitude. In addition, the corrosion current decreased by 50%, and the impedance doubled in a 3.5 wt% NaCl solution saturated with CO₂. Thus, the multilayer (Si-DLC)₄₀ film on the inner wall of the N80 tube exhibited superior tribological properties and exceptional corrosion resistance. These findings are anticipated to furnish valuable data and technical insights for mitigating corrosion in N80 steel pipes during petroleum exploitation.

The corrosion and wear of N80 pipeline in oil and gas field environment has always been an urgent problem to be solved in the field of oil and gas exploitation. DLC film is considered to be an effective material for prolonging the service life of pipeline due to its excellent properties. However, it is very difficult to deposit a uniform DLC film on the inner surface of long pipeline. In this paper, DLC film was deposited on the inner surface of a 1 m-long N80 pipeline with an inner diameter of 75 mm by hollow cathode plasma enhanced chemical vapor deposition (HC-PECVD) using the pipeline itself as the deposition chamber and cathode. The uniformity of microstructure, mechanical properties, corrosion resistance and tribological properties of DLC film were discussed. The results show that the DLC film deposited on the inner surface of N80 long pipeline by HC-PECVD equipment possesses excellent axial uniformity. The deposition of DLC film increases the corrosion potential and reduces the corrosion current density, which greatly improves the corrosion resistance of N80 pipeline. In addition, the deposition of DLC film also reduces the friction coefficient and wear rate, which greatly improves the wear resistance of N80 pipeline. Therefore, the deposition of DLC film is an effective protection method for the inner surface of N80 pipeline, which prolongs the service life of the pipeline. HC-PECVD equipment with pipeline as cavity uniformly deposits DLC film on the inner surface of long pipeline, which is a potential deposition method to prolong the service life of long pipeline in oil and gas exploitation.

Humid air is a very important service environment, in which metal friction parts should be enhanced to offer excellent corrosion resistance and wear resistance. The B₄C coating is an excellent candidate material to enhance the corrosion resistance and tribological behaviors. The purpose is to investigate the effect of negative bias voltages on the tribological properties of B₄C coatings under a high relative humidity environment. Amorphous B₄C coatings were successfully prepared by closed field unbalanced magnetron sputtering technology and its microstructure, hardness, elastic modulus, adhesive force and tribological properties were systematically studied. Results demonstrate that the B₄C coatings deposited at each negative bias voltage have a columnar structure and the surface roughness remained unchanged (about 1.0 nm), while the thickness, hardness, elastic modulus and adhesion force increase first and then decrease with the negative bias voltage increasing. Among them, the B₄C (−50 V) coating showed the best mechanical properties. It should be noted that the B₄C (−50 V) coating with an excellent corrosion resistance also exhibits the lowest friction coefficient (~0.15) and wear resistance (7.2 × 10⁻⁷ mm³·N⁻¹·m⁻¹) under humid air (85% RH). This is mainly due to the tribochemical reaction of B₄C during a sliding process to produce boric acid at the sliding interface. B₄C coatings can provide an excellent corrosion resistance and high wear resistance due to their high chemical stability and high hardness.