Abstract
The working environment for tubing in oil and gas fields is becoming more and more serious due to the exploration of unconventional oil and gas resources, leading to the increasing need for a protective internal coating to be used in tubing. Therefore, a new mica–graphene/epoxy composite coating with different graphene contents (0.0, 0.2, 0.5, 0.7, and 1.0 wt.%) was prepared to improve the tubing resistance to a corrosive medium, an autoclave was used to simulate the working environment, and an electrochemical workstation assisted by three-electrodes was used to study the electrochemical characteristics of the coating. The results showed that the addition of a certain amount of graphene into the mica/epoxy coating significantly improved the corrosion resistance of the composite coating, and when the graphene content increased, the corrosion resistance of the mica/epoxy coating first increased and then decreased when the corrosion current density of a 35 wt.% 800# mica/epoxy coating with a 0.7 wt.% graphene content was the lowest (7.11 × 10−13 A·cm−2), the corrosion potential was the highest (292 mV), the polarization resistance was the largest (3.463 × 109 Ω·cm2), and the corrosion resistance was improved by 89.3% compared to the coating without graphene. Furthermore, the adhesion of the coating with 0.7 wt.% graphene was also the largest (8.81 MPa, increased by 3.4%) and had the smallest diffusion coefficient (1.566 × 107 cm2·s−1, decreased by 76.1%), and the thermal stability improved by 18.6%. Finally, the corrosion resistance mechanism of the composite coating with different graphene contents at different soaking times was revealed based on the electrochemistry and morphology characteristics other than water absorption and contact angle.
Highlights
Licensee MDPI, Basel, Switzerland.In the process of oil and gas exploitation, gathering and transportation, there are often many corrosive species in the produced fluid, such as H2 S, Cl−, CO2, etc
The preparation processes to develop the coating in this experiment were divided into two steps: The first step was to prepare a 35 wt.% 800# (800 mesh) mica/epoxy coating, and the specific method was as follows: 35 wt.% 800# mica powder filler was mixed with epoxy resin (E-08), and stirred at 1200 r/min for 1 h, and it was dispersed by ultrasonication for 1 h so that the filler was fully dispersed in the coating
When the graphene content in the coating was 0.7 wt.%, the self-corrosion potential of the composite coating was 292 mV, which was higher than that (−332 mV) presented in reference [30], indicating the corrosion tendency decreased from the perspective of corrosion thermodynamics
Summary
While many fillers (organic, inorganic, etc.) are introduced into epoxy resin, which can enhance the protection performance of the coating and can further hinder the contact between the metal matrix and the corrosive medium. This has improved the corrosion resistance of pipes and has attracted widespread attention. Researchers have found that the addition of graphene into epoxy resin effectively improves the shielding performance, strong acid and alkali resistance, and adhesion of coatings [11,19]. Materials 2022, 15, 1194 graphene/epoxy, the corrosion resistance mechanism of the composite coatings with different graphene contents at different soaking times was revealed
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