
Representatives of the GERG project HYSTIC (Hydrogen in Service Tightness Criteria) began on 9 July the project’s fitting tests at Kiwa’s facilities. Sander Lueb, Gas Technical Consultant at Kiwa, hosted Joshua Woods, Asset Engineer at Gas Networks Ireland; Yohan Laurent, from the Technical Centre for Mechanical Industries (CETIM), and Miguel Andriano, R&D Engineering Trainee at CETIM, representatives from HYSTIC partners.
The fittings tested – intended for use in monitoring and process lines at pressure-reducing stations – cover a wide range of diameters, and will undergo a comprehensive programme of type-approval testing. The tests include axial and flexural loads, vibration tests, temperature cycling, reassembly, and over-torque testing. Once these tests have been completed, the samples will be examined to verify their tightness against hydrogen leaks.
Fittings are one of the types of equipment being evaluated in HYSTIC, alongside flange gaskets, valves and pressure regulators. Through all these tests, the project will assess the sealing performance under operating conditions of various materials and equipment used in H₂ applications. Based on the test results, it will be possible to define realistic tightness classes for the different materials and equipment tested, along with the associated protocols. This work will help to compare the tightness performances of different types of equipment and in controlling the emission level of their installation.
Projects like HYSTIC promote the uptake of hydrogen, but also tackle various engineering challenges related to a broader hydrogen introduction: Higher material permeability than methane, accelerated material degradation mechanisms, higher sealing and assembly precision requirements, and performance validation under dynamic operating conditions. By rigorously testing fittings across multiple stress scenarios, HYSTIC helps network operators understand which materials, designs, and installation practices are truly fit for hydrogen service. This knowledge directly supports safe conversion of existing gas infrastructure and reduces uncertainty for future investments.
As Europe prepares its gas networks for hydrogen, every component — even small fittings — becomes critical. Hydrogen is a lighter, more diffusive molecule than natural gas, and ensuring leak‑tightness under real operating conditions is essential for network safety, reliability, and public confidence. Qualifying these fittings is therefore a foundational step toward large‑scale hydrogen integration. Hydrogen can also cause hydrogen embrittlement, which relates to a different fatigue behavior of the material, however considering this material is 316 stainless steel, which stable austenitic structure isn’t susceptible for hydrogen embrittlement due to gaseous hydrogen charging.
There is also a slight differences of the thermal expansion co-efficient of air and hydrogen at 100 bar where hydrogen is 15% higher, which would enable it to apply slightly higher stress on the material. However, due to difficulties with test set up this effect has been disregarded.


















