Hydrogen vapour permeability testing

 

Hydrogen vapour permeability testing is critical for materials used in applications such as hydrogen storage, fuel cells, and pipelines, where hydrogen's small molecular size and high diffusivity can pose significant challenges.

Key Concepts

• Permeability: Permeability is the measure of how easily a gas or vapour can pass through a material. For hydrogen, this is critical due to its small molecular size and high diffusivity.  Hydrogen has the highest vapour permeability of any gas and thus can be difficult to contain.
  
  
• Diffusivity: This refers to the rate at which hydrogen molecules spread through the material. High diffusivity means hydrogen can quickly penetrate the material.
  
  
• Solubility: This is the amount of hydrogen that can be absorbed by the material. High solubility means more hydrogen can be absorbed before it starts permeating through.
  
  
• Fick's first and second laws are crucial to to understanding the physics of hydrogen vapour permeability as they quantify the rate at which hydrogen diffuses through materials, helping in the design and selection of materials with appropriate permeability characteristics to ensure safety and efficiency in various applications. This laws provide the mathematical foundation to predict and control hydrogen transport in medical, industrial, and storage systems.
  
  

Testing Process

• Sample Preparation: A sample of the material to be tested is prepared, typically in the form of a thin film or membrane.
  
  
• Setup: The sample is placed in a permeation cell, which is a sealed chamber divided into two compartments by the sample material. One compartment is exposed to hydrogen gas at a controlled pressure, and the other compartment is either under vacuum or filled with an inert gas. Other setups allow for the permeability testing of components, entire systems or products. For some applications it is important to be able to vary environmental conditions such as temperature, pressure and vapour pressure.
  
  
• Permeation Measurement: Hydrogen gas is introduced to the high-pressure side. Over time, hydrogen molecules diffuse through the material and emerge on the low-pressure side. The accumulation or rate of hydrogen flow on the low-pressure side is measured.
  
  
• Data Analysis: The permeability coefficient is calculated using the measured flow rate, the thickness of the material, and the pressure differential across the material. This coefficient provides a quantitative measure of the material's resistance to hydrogen permeation.

Factors Affecting Hydrogen Permeability

• Material Type: Different materials have varying resistance to hydrogen permeation. Metals, polymers, and composites each behave differently.
  
  
• Temperature: Permeability usually increases with temperature due to increased molecular activity.
  
  
• Pressure: Higher hydrogen pressures can lead to higher permeation rates.
  
  
• Material Thickness: Thicker materials generally offer more resistance to permeation, but this is not always linear.
  
  

Applications

• Hydrogen Storage Tanks: Ensuring that materials used in storage tanks have low hydrogen permeability to prevent leaks.
  
  
• Fuel Cells: Assessing materials used in fuel cells to ensure they can efficiently contain and transport hydrogen without significant losses.
  
  
• Pipeline Materials: Evaluating pipeline materials for their ability to transport hydrogen safely over long distances.
  
  
• See our Hydrogen applications page for more industries where hydrogen permeability is important
  
  

Importance

• Safety: Preventing hydrogen leaks is crucial for safety, as hydrogen is highly flammable and can embrittle pipelines and containers.
  
  
• Efficiency: Minimizing hydrogen loss improves the efficiency of hydrogen-based systems.
  
  
• Material Selection: Helps in selecting appropriate materials for specific applications involving hydrogen.

Standards and Guidelines

Various standards and guidelines exist for hydrogen permeability testing, provided by organizations including ASTM International, ISO, and other industry bodies. These standards ensure consistency and reliability in testing procedures and results.

Hydrogen vapour permeability testing is an essential process for evaluating the suitability of materials in hydrogen-related applications, focusing on safety, efficiency, and material performance.