Valve World Magazine November 2025 | Seite 27

CRYOGENIC VALVES separates the stem packing from the cryogenic fluid, allowing it to remain at near-ambient temperatures. This prevents packing embrittlement and ensures longterm sealing reliability( Hartmann Valves, 2015; Abdullah et al., 2017). Extended bonnets also minimise frost buildup around operating components, which can obstruct manual operation and increase torque requirements. In LNG shipboard applications, extended bonnets help avoid dangerous icing near operator interfaces, enhancing safety for crew( Sim, 2021). For liquid hydrogen, bonnets play a critical role in reducing helium permeation and maintaining mechanical alignment under thermal cycling( Ivancu & Popescu, 2023). Computational fluid dynamics( CFD) studies have confirmed that bonnet length and geometry significantly influence vapour column stability and insulation effectiveness( Zhang et al., 2020). Empirical tests show that each 100 mm increase in bonnet length can reduce stem packing temperature by 15 – 20 ° C during steadystate cryogenic flow. Future innovations in bonnet design are targeting modular geometries that allow customised length based on system insulation, lightweight alloys to reduce offshore topside loads, and integrated heat barriers that lower conduction losses( Emerson, 2017; Garcia & Martinez, 2025).

Figure 2. Extended bonnet cryogenic valve under assembly, developed to handle extreme thermal contraction and ensure long-term performance

Seat and seal technologies: From PTFE to metal-to-metal at extreme cold

Sealing systems in cryogenic ball valves must endure thermal contraction, abrasion and cyclic stresses. Traditional PTFE soft seats offer bubble-tight shutoff but risk deformation at ultra-low temperatures. To address this, hybrid designs incorporate PTFE / PEEK composites or transition to metalto-metal sealing with tungsten carbide, Stellite, or NiCr overlays( Cyrus, 2016; Abdullah et al., 2017).

Table 2. Comparative performance of cryogenic seat and seal materials; Data compiled from cryogenic valve testing studies, CFD / FEA simulations and standard requirements

PTFE( virgin) – 100 …+ 180 1E – 4 … 1E – 5 Low – Med Poor

Lowest torque & cost; creep below – 150 ° C possible

( API, 2021; Ivancu & Popescu, 2023)

UHMW-PE – 150 …+ 100 1E – 5 … 1E – 6 Med Poor

PEEK – 150 …+ 250 1E – 5 … 1E – 6 High Fair

Low friction; cold flow under load

Strong, wear-resistant; higher torque

( Sim, 2021; Xie & Li, 2023)

( Abdullah et al., 2017; Emerson, 2017)

Metal-to-Metal – 196 …+ 500 1E – 3 … 1E – 4

Very High

Good Fire-safe, survives fire; torque( Cyrus, 2016; Habonim, 2022)

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