[ permeation ]
permeability coefficient of a material is known , one can calculate the permeation rate for a range in dimensions and situations .
The amount of hydrogen permeation
In the article
Modern PE pipe enables the transport of hydrogen , the loss of hydrogen due to permeation is determined for a polyethylene ( PE ) pipe that is often used for the transport of natural gas . From the permeation experiments a permeability coefficient of 126.8 ( ml · mm )/ ( m
2 · day · bar ) for hydrogen is derived . For comparison , in the article a permeability coefficient for methane of 56 ( ml · mm )/ ( m
2 · day · bar ) is given . So , for this PE pipe , the permeation rate for hydrogen gas is about 2.3 times higher compared to methane .
( Yes , we know : the permeability coefficient has a complex-looking unit , but this is unfortunately a necessity . It contains all the elements of the parameters mentioned above , such as the thickness of the pipe wall expressed in mm , the surface area in m 2 , and the difference in partial pressure expressed in bar .)
The benefits of knowing the permeation behavior
Last but not least , why are the permeation behavior and quantification of the permeation rate important ? As already pointed out in the introduction , the three main reasons are :
• Safety , e . g ., due to the accumulation of flammable gases outside the enclosed volume ,
• Emissions , e . g ., in the case of a greenhouse gas ,
• An economical perspective , where the permeate represents a value .
With the envisioned large-scale application of hydrogen in the current efforts for decarbonization , it is important to at least quantify the permeation for safety purposes . Similar to the loss of hydrogen gas via permeation , permeation
Fig . 2 . Permeation block used to hold a material sheet , taken from a permeation measurement set-up
of gaseous components from the environment can permeate into the pipe , such as nitrogen gas . This results in a change of the hydrogen quality and could potentially affect appliances and processes where the hydrogen purity is a key aspect . As you can see , there are many interesting reasons to give permeation the proper attention .
Ensuring confidence through quality and testing
Permeation is not yet described in many standards for , e . g ., gas transport and distribution through pipes . But within the energy transition it is a topic which is receiving more and more attention . Many parties in the hydrogen chain are now looking into this topic , asking questions to quantify permeation for their products . At Kiwa , we have experience with permeation testing for a variety of components , and we help our customers by doing the permeation experiments and the corresponding interpretation and use of these data for assessments .
About the authors
20 Hydrogen Tech World | Issue 8 | February 2023