Radosław Sieczkowski, Phd
Head of Technical Department, SPETECH^®

The sealing of industrial installations for natural gas, its mixture with hydrogen, and pure hydrogen as a fuel of the future face specific requirements, which must secured: corrosion resistance, sufficiently high gas tightness, fire safety, electrical conductivity (in grounded systems), prevention of electrostatic charge accumulation in explosion hazard zones.

Hydrogen Corrosion
Natural gas, whether high-methane or nitrogen-rich, is a well-understood medium. Even with additional impurities, it does not pose corrosion problems for most sealing materials currently produced from steel, flexible graphite, PTFE, or some elastomers. Hydrogen, however, presents a challenge due to the risk of Hydrogen Impact Cracking [HIC] , also known as hydrogen corrosion.
Hydrogen corrosion arises partly from the reaction of hydrogen (H₂) with carbon (C) present in steel. A known phenomenon is the decarburization of steel in the subsurface layer. This reaction produces methane (CH₄) molecules that are relatively large and cannot diffuse through the metallic phase, so methane accumulates where it's formed—mainly at grain boundaries, in micropores, or structural defects. The pressure from accumulating methane causes stresses that eventually lead to cracking (see Figs. 1a and 1b).

 
Figs. 1a and 1b. Cracking caused by hydrogen interaction

Author: Artur Jasiński - Department of Chemistry and Diagnostics "ENERGOPOMIAR"

Commonly used materials that resist this effect include austenitic (acid-resistant) steels from the AISI 304 and AISI 316 groups. These are standard in SPETECH^® RTJ ring type metal seals, SWG spiral-wounds as well as our serrated profiles (see Figs. 2a and 2b), which are traditionally used in gas and petroleum industries. In other words, blending hydrogen for co-combustion with natural gas generally doesn't require changing sealing material types. Even pure hydrogen poses no major challenge for current solutions.

 
Fig. 2a: SPETECH^® Spiral Wound Gasket; Fig. 2b: SPETECH^® Serrated Gasket 

Gas tightness
Hydrogen places greater demands on gas tightness. Gas tightness of static seals is tested according to EN13555 using helium as a test medium. It’s assumed that hydrogen tightness should not significantly deviate from helium tightness, although work is ongoing to adopt hydrogen as a test medium under EN13555. Existing studies confirm that high-quality spiral-wound and multi-edge seals can achieve extremely high tightness classes—orders of magnitude above the commonly accepted standard of 0.01 mg/(m·s). An example of achievable tightness values versus gasket load is shown in Fig. 3.

Fig. 3: Qmin/L and Qsmin/L coefficients vs. EN13555 tightness class at 80 bar for SPETOMET^® MWK^® 60 gasket

Fire safety
Another challenge in sealing flammable and explosive media is fire safety. Fire safety requirements are stated in section 2.12 of the Essential Safety Requirements of Directive 2014/68/EU (Pressure Equipment Directive).
Fire safety implies no leakage during a fire and post-exposure. A seal must not only be non-flammable but also retain tightness under fire and after cooling. Several test standards assess the fire safety of valves with static seals or flanged joints, including: BS 6755-2, ISO 10497, API 607, API 6FA, API 6FB.
From a static seal perspective, API 6FB appears most appropriate, involving testing a gasket in ASME B16.5 blind flanges (NPS 6”, class 300). The test setup is shown in Fig. 4. Example fire safety certificates are shown in Figs. 5a and 5b.

Fig. 4: AMTEC Messtechnischer Service GmbH fire test setup per API 6FB

 
Figs. 5a and 5b: Fire safety certificates per API 6FB for SPETECH Spiral Wound Gasket and Serrated Gasket 

Electrical Conductivity and Antistatic Properties
Fire safety also relates to seal electrical conductivity, enabling discharge of electrical charges from lightning. Metallic and metal-graphite seals have very low resistivity:
•    steel components: 0.07 × 10⁻⁶ Ωm
•    expanded graphite filler: 68 × 10⁻⁶ Ωm
These values ensure continuous electrical conduction in installations.
The final safety requirement is antistatic properties, essential in explosive zones. Good electrical conductivity in seals also prevents electrostatic charge accumulation, confirmed by resistance and resistivity tests. For these, EN 61340-2-3 can be applied. The test setup is shown in Fig. 6, where both surface and through resistance/resistivity are measured, with the standard defining maximum values to ensure safety.

Fig. 6: Test setup for resistance and resistivity per EN 61340-2-3
 

Summary:
SPETECH^® RTJ ring type metal seals, SWG spiral-wounds as well as our serrated profiles made of 316L steel and FG-C graphite meet the highest tightness and safety standards for natural gas and hydrogen mixture installations.
However, due to the growing importance of hydrogen in industrial applications, we continue research on our special metal seals. Such work is possible thanks to our own SPETECH^® Research and Testing Laboratory, where we are capable to test with usage of hydrogen, methane and helium as testing media.