Plastic housing for industrial speed sensors.

The hydrogen industry is blooming, offering a clean and sustainable alternative to traditional energy sources. However, ensuring the safe and efficient operation of this technology requires a network of unseen heroes—sensor housings and mounts. These seemingly simple components play a key role in safeguarding sensitive sensors and ensuring the smooth flow of hydrogen.

These components protect sensors from harsh hydrogen environments and provide durability, structural integrity, and stability. Hence, you should know the functions and design considerations of sensor housings and mounts in the hydrogen industry. 

But first, let’s start by defining what sensor housings and mounts are in the hydrogen industry.  

What are Sensor Housings and Mounts in the Hydrogen Industry? 

Sensor housings and mounts are the unsung heroes of the hydrogen industry. These seemingly simple components play a critical role in safeguarding sensitive sensors and ensuring the smooth operation of hydrogen production, transportation, and storage facilities. 

They play different roles in the hydrogen industry, such as;

• Protection: Hydrogen environments can be harsh. Housings protect against physical damage from impacts, vibrations, and flying debris. They also protect sensors from dust, moisture, and extreme temperatures, which can compromise sensor performance or even lead to failure.
• Controlled Environment: Maintaining a stable environment around the sensor is crucial for accuracy and precision. Housings can provide thermal insulation to minimize temperature fluctuations and may even incorporate features for active temperature control in extreme environments.
• Calibration and Maintenance: Well-designed housings allow for easy access to sensors for calibration and maintenance without compromising the system’s overall integrity.

You’d agree that sensors and mounts are not negotiable in the hydrogen industry. Let’s consider the structure of these components. 

Structures of Sensor Housings and Mounts in Hydrogen Industry.

Material Selection. 

Choosing a suitable material is paramount. Here’s a closer look at popular options and their advantages:

• Stainless Steel (316L Grade): This golden standard offers excellent resistance to corrosion, good mechanical strength, and the ability to withstand a wide range of temperatures. However, some grades of stainless steel are susceptible to hydrogen embrittlement, a phenomenon in which hydrogen exposure weakens the metal.
• Monel: A nickel-copper alloy prized for its exceptional resistance to hydrogen embrittlement. It boasts superior corrosion resistance compared to some stainless steels but is cheaper.
• Hastelloy: A family of high-performance alloys specifically designed for harsh environments. Different Hastelloy variants offer varying resistance to specific corrosive agents, including hydrogen. Despite being the most expensive option, they are often the material of choice for highly critical applications.
• Pressure Rating: The housing must withstand the specific pressure conditions within the hydrogen system. This factor heavily influences the choice of material, wall thickness, and overall design of the housing.
• Ingress Protection (IP rating): This international standard defines the level of protection against dust and water ingress. An IP rating of 65 or higher is often preferred for hydrogen applications. An IP65 rating signifies complete dust protection and resistance to water jets from any direction. Higher ratings offer even more excellent protection against water immersion.
• Ventilation: In some cases, hydrogen build-up within the housing can be a concern. Ventilation strategies, such as strategically placed vents or breathable membranes, may be necessary to prevent this or manage heat dissipation for sensors that generate significant heat.
  
• Mounting Options: Mounts should be designed for simple and secure installation. They should also allow for easy adjustment to ensure proper sensor alignment and facilitate removal for maintenance. Depending on the application, options like threaded connections, flange connections, or quick-release mechanisms can be employed.

Manufacturing Techniques for Sensor Housings and Mounts

There are various manufacturing techniques, each offering distinct advantages and limitations. Below are a few;

CNC Machining.

A computer-controlled machining process that allows for the creation of complex, high-precision housings and mounts from solid metal blocks. This method is ideal for small-scale production or applications requiring intricate designs. However, it can be time-consuming and expensive in large quantities.

• Advantages: High precision, repeatability, and the ability to produce complex geometries.
• Applications: Suitable for producing custom or low-volume sensor housings and mounts with tight tolerances.

Metal Casting.

A cost-effective method for producing large quantities of housings with simpler geometries. Molten metal is poured into a mold cavity that defines the final shape of the housing. This technique efficiently replicates the same design but may not be suitable for complex shapes.

• Advantages: Capable of producing consistent quality sensor housings and mounts in large quantities.
• Applications: Ideal for mass production of standardized sensor housings and mounts.

Sheet Metal Fabrication. 

This process involves cutting and shaping sheet metal into the desired form. It’s a good option for creating lightweight housings with good formability for specific shapes. However, sheet metal housings may not be suitable for high-pressure applications due to their inherent limitations in strength.

• Advantages: Cost-effective for producing sensor housings and mounts with simpler designs or larger quantities.
• Applications: Commonly used for producing sensor mounts and brackets with standard shapes and sizes.

Injection Molding.

A rapid and cost-efficient method for producing complex plastic housings in large quantities. Molten plastic is injected into a mold cavity to create the desired shape. This method is ideal for less demanding environments where pressure resistance is not critical. However, some plastics may not be compatible with hydrogen or may degrade over time when exposed to hydrogen.

• Advantages: High-volume production capability, consistency, and the ability to produce complex shapes.
• Applications: Suitable for producing plastic sensor housings and mounts in large quantities.

3D Printing.

An emerging technology with the potential to revolutionize sensor housing design. 3D printing allows for the creation of custom-designed housings with complex geometries on demand. However, material selection for 3D printing in hydrogen applications is crucial. Not all 3D printing materials offer the strength, chemical resistance, and temperature tolerance required for the hydrogen environment.

• Advantages: Rapid prototyping, customization, and the ability to produce complex geometries without molds.
• Applications: Ideal for prototyping, customization, or low-volume production of specialized sensor housings and mounts

Surface Finishes for Sensor Housings and Mounts. 

Let’s take a closer look at how surface finishes influence sensor housings and mounts in the hydrogen industry:

Electropolishing. 

This process involves using an electric current to remove a microscopic material layer from the surface. This process improves the surface finish by smoothing out microscopic “peaks and valleys,” resulting in a shiny, smooth surface.

• Enhanced Corrosion Resistance: Electropolishing improves the material’s resistance to degradation from hydrogen exposure by removing surface imperfections where corrosion can initiate.
• Reduced Particle Entrapment: A smooth surface minimizes the potential for contaminants and moisture to adhere, leading to more accurate sensor readings and reduced risk of sensor malfunction.
• Improved Cleanliness: Electropolishing simplifies cleaning and maintenance procedures, promoting overall system hygiene.

Passivation. 

This process involves forming a thin oxide layer on the material’s surface through chemical treatment. Passivation is crucial for stainless steel sensor housings and mounts in the hydrogen industry to prevent corrosion and maintain material integrity, ensuring long-term performance and reliability. 

• Enhanced Corrosion Resistance: The oxide layer acts as a barrier, hindering the interaction between the metal and hydrogen, thereby improving corrosion resistance.

Anodizing.

Anodizing, an electrolytic process that forms a protective oxide layer on the surface of aluminum and its alloys, is primarily used for aluminum housings.  Anodizing creates a protective oxide layer that offers several advantages, such as;

• Improved Wear Resistance: The hardened oxide layer enhances the housing’s resistance to scratches and abrasions, which is particularly beneficial in environments with high mechanical wear.
• Electrical Insulation: The oxide layer provides a degree of electrical insulation, which can be crucial for specific sensor applications.
• Enhanced Corrosion Resistance: Similar to passivation, the oxide layer offers some protection against corrosion. However, it’s important to note that anodizing may not be as effective as electropolishing or using specific corrosion-resistant alloys for hydrogen applications.

Bead Blasting.

Bead blasting, also known as abrasive blasting, involves projecting tiny beads at high velocity onto the surface of a component to create a matte or textured finish. Bead blasting removes surface contaminants, imperfections, and oxides, resulting in a clean and uniform surface.

Some other benefits include;

• Improved Adhesion: The textured surface provides a better foundation for paint or other coatings, further enhancing corrosion protection or improving aesthetics.
• Stress Relief: Bead blasting can help relieve residual stresses from the manufacturing process, improving the housing’s overall strength and fatigue resistance.

Choosing a suitable surface finish depends on various factors, such as the specific material of the housing, the intended environment, and desired properties. For instance, electropolishing is often preferred for its superior corrosion resistance and cleanability, while bead blasting might be combined with painting for housings exposed to harsh weather conditions.

Conclusion

Sensor housings and mounts may seem like simple components, but they play a vital role in hydrogen systems’ safe, reliable, and efficient operation. Understanding the functions, design considerations, manufacturing techniques, surface finishes, and emerging trends can help create robust sensor housings and mounts that can withstand the demanding environments of the hydrogen industry.