Parylene Conformal Coatings for Oil & Gas Sensors

Parylene, a transparent polymer, provides seamless and void-free conformal coatings. Variants like Parylene N, C, D and Parylene HT® are crafted through molecular structure tweaks, each yielding distinct material properties for various applications. Among these derivatives, the fundamental type is Parylene N, derived from the poly-para-xylylene monomer.

Parylene presents numerous benefits for application in the electronics industry and sensor technology. Its ability to thoroughly penetrate into crevices and voids, while coating sharp edges and surfaces, ensures exceptional sealing for underlying structures. Within sensor technologies, Parylene conformal coatings are valued for their insulating, dielectric, and protective attributes. Refer to the table below for an extensive list of their properties.

The Parylene Deposition Process:

The chemical vapor deposition (CVD) process of Parylene takes place in three steps: sublimation, pyrolysis and deposition). The final coating is applied onto the desired surface (elastomer, glass, metal, paper, plastic, etc.). To enhance adhesion, meticulous surface cleaning is carried out. Afterwards, the sample surfaces undergo treatment with an adhesion promoter like silane (A-174). This promoter creates a monolayer of molecules, establishing a robust bond interface between the surface and the Parylene coating. Samples can be batch processed in a Parylene vacuum chamber. The temperature and pressure are set for the ideal coating conditions. The coating process takes place once the Parylene powder precursor (Paracyclophanes, dimer) is sublimized and pyrolised forming the monomers. Pyrolysis of the precursor is defined as the thermal decomposition of materials at elevated temperatures in an inert atmosphere and this reaction is irreversible. Afterwards, monomers are deposited as a thin layer in a way to allow for a top layer to grow on them. Meanwhile, the monomers permeate even the tiniest voids, creating a flawless, uniform conformal coating without any gaps. The thickness of the Parylene can be precisely adjusted based on the specific application requirements.

Oil & Gas Sensors

Sensors can detect and help in monitoring the dynamic behavior (temperature, pressure, electric current) of a target under different atmospheric conditions (ie. gaseous, liquid media, temperature, pressure.). The data collected using these sensors contribute to the continuous operation in the oil and gas industry. The data provides important statistics from which shutdowns, risks and emergencies or optimal conditions can be predicted before an event occurs. To allow for a profitable business operation sites must be well maintained and monitored to keep the cash flowing during the high times of the demand. Oil well pressure sensors regulate the liquid levels in the tanks to prevent explosions and, gas sensors help in the detection of a variety of gases such as O₂, H₂O, CO₂, H₂S, Methane and others. Unites States O&G exploration and production direct corrosion costs were reported as ≈$1.4 billion annually with $589 million attributed to the surface piping and facility costs, $463 million to downhole tubing expenses, and $320 million to capital expenditures related to corrosion [1], [2].

Because, corrosion and harsh environments are a huge concern that entails a high cost in the production and subsequent operations due to the ware of instrumentation the intensely used pipelines and instrumentation requires monitoring by oil and gas sensors. Deep waters offshore, remote arctic locations and reservoirs with unconsolidated sands are the primary sites of exploration. The most challenging sites for use of instrumentation are characterized by the high pressures and high temperatures (HPHT) and the design guidelines for equipment that are used in areas with pressures greater than 15 ksi (103.43 MPa) and temperatures greater than 350°F (177°C) (i.e. deep waters 800 – 1800 m) are determined by the American Petroleum Institute [2], [3]. Looking at this big picture sensors are the essential parts of successful operations in the oil and gas exploration and production industry. These sensors and materials used in their production need to satisfy the durability and thermal stability guidelines among with being able to withstand exposure to a variety of corrosive environments.

Parylene derivatives offer high durability, wear resistance, low friction, low gas and humidity permeability, and relatively high thermal resistance which makes them a favorable candidate for sensor applications either as a protective sealing or as an insulator to be used in the production of sensors. Also, Parylene protective coatings can withstand cryogenic and relatively high temperatures (-400°F (-200°C) to +400°F (+200°C)) while maintaining their electrical and mechanical properties which is a rare property in materials systems. Ensuring repeatability, process control and understanding materials’ behavior in diverse conditions is crucial for the response of integrated electronic circuits in sensor development. Parylene’s high dielectric strength makes the conformal coating favorable for use as insulators and the dielectric properties can be tuned by modifying the coating thickness.

Once applied Parylene acts as a chemically resistant barrier against gases (O₂, N₂, CO₂, H₂, etc.), humidity (low permeability), corrosion (high chemical resistance) and provides wear resistance (low coefficient of friction) for a long term (>10 years) under harsh conditions. Parylenes C and N are widely used coatings that meet temperature requirements up to approximately 100°C in oxidative conditions. In contrast, fluorinated Parylene HT offers enhanced thermal stability, reaching 350°C. Leveraging Parylene derivatives for sensor development and protecting components in harsh environments proves effective. Parylene is poised to advance sensor technology for demanding conditions like high pressure, high temperature (HPHT) conditions, deep-sea and arctic environments.

References:
[1] N. Koch, G.H.; Brongers, M.P.; Thompson, N.G.; Virmani, Y.P.; Payer, J.H., “Corrosion Costs and Preventive Strategies In the United States,” p. 12.
[2] M. Iannuzzi, A. Barnoush, and R. Johnsen, “Materials and corrosion trends in offshore and subsea oil and gas production,” Npj Mater. Degrad., vol. 1, no. 1, pp. 1–11, Jul. 2017.
[3] P. Bunch, S. Shademan, and A. Bajvani, “Material Characterization Procedure for High Pressure High Temperature Applications Using API 17TR8 Criteria,” presented at the Offshore Technology Conference, 2017.