Cryogenic Seals for LNG and Industrial Gas Systems

Cryogenic seals work in a very harsh corner of engineering.

Temperature is far below zero. Media can be LNG, liquid nitrogen, oxygen, or hydrogen.

If the seal fails, the system may leak, freeze, or even form dangerous ice plugs.

As a specialized cryogenic seal manufacturer, we design seals that stay tight from cool-down to warm-up.

This article gives an engineer-level view of how these seals work and how to specify them for real projects.

1.What Makes Cryogenic Seals Different?

Most standard seals come from elastomers.

At very low temperature, many elastomers turn stiff or brittle.

Hardness increases. Elastic recovery drops. Leakage starts.

Cryogenic seals must also handle:

• Large thermal contraction of metal housings
• Rapid pressure changes during filling and emptying
• Vibration and stem movement in valves and pumps
• Media compatibility with LNG, LOX, LIN, LAr, LH₂ or mixed hydrocarbons

The seal must keep contact pressure on the hardware in all these states.

It must also survive HPHT / PV conditions during transient operation.

2. Core Cryogenic Seal Designs

The images on this page show our main cryogenic seal families.

Each design targets one typical problem in LNG and industrial gas equipment.

2.1 Spring Energized Cryogenic Seals

Spring energized seals use a PTFE or engineered plastic jacket plus a metal spring.

The spring pushes the lips outwards.

System pressure then actuates the lips, enhancing the sealing force.

Typical uses:

• LNG nozzle spring energized seals – seal between nozzle and receptacle.
• Cryogenic ball valve stem seals – maintain tightness during stem movement.
• Piston and lip seals – for cryogenic pumps and control valves.

These seals give reliable sealing even when the hardware shrinks at low temperature.

The spring compensates for polymer creep, thermal contraction, and wear over extended service life.

2.2 Ball Valve Seat Seals for Cryogenic Service

Ball valve seat seals in LNG service must seal in both directions.

They must also pass low-leakage tests after thermal shock cycles.

Our seat seals use filled PTFE or similar materials plus metal energizers where needed.

Design focus points:

• Bidirectional sealing for high-pressure ball valves
• Stable torque at low temperature
• Controlled contact stress to avoid seat damage

We supply cryogenic seals for valve seats in liquefaction plants, LNG carriers, and loading arms.

For API 6D pipeline ball valves in LNG service, we also provide complete seat, stem, and piston seal packages. 

You can view more details here: API 6D Ball Valve & LNG Seal Solutions.

2.3 Stem, Piston, and Lip Seals

Stem and piston seals in cryogenic ball valves and API 6D valves need:

• Low friction during actuation
• No stick-slip after long static periods
• Good sealing during small side loads and misalignment

Our helical spring ball valve stem seals and high-pressure lip seals combine:

• A low-temperature PTFE-based sealing ring
• A corrosion-resistant spring (such as stainless steel or nickel alloy)
• Hardware grooves that control extrusion and prevent blow-out

This design helps maintain a tight seal envelope even under high differential pressure.

2.4 Metal-Face and Composite Seals

Some seats and stem areas use a metal-to-metal design with a thin PTFE interface.

Here we use metal face spring-energized PTFE seals.

The metal body gives structural support for high load.

The PTFE layer provides the actual sealing surface.

The spring element maintains contact pressure as parts move with temperature.

3. Material Choices for Cryogenic Seals

Material selection is critical.

The wrong combination can crack, creep, or leak during thermal cycling.

Common polymer choices for cryogenic seals:

• PTFE and filled PTFE – excellent low-temperature flexibility and chemical resistance.
• Special engineered plastics – for higher wear or lower permeation where PTFE alone is not enough.

Spring and reinforcement materials:

• Stainless steel for general industrial gas service
• High-nickel alloys (such as Elgiloy-type materials) for aggressive media or higher fatigue life

During design we check:

• Thermal expansion match between seal and hardware
• Creep and relaxation at stand-by temperature
• Permeation and blister resistance during warm-up
• Requirements for oxygen compatibility, cleanliness, and degreasing

4. How to Specify Cryogenic Seals for Your Project

When you prepare a data sheet or RFQ, try to give the following points.

It helps us as a cryogenic seal manufacturer to design the right solution fast.

Medium and purity level

• LNG, liquid nitrogen, liquid oxygen, helium, hydrogen, or mixed gases.

Temperature range

• Cool-down temperature, normal operating temperature, and maximum warm-up.

Pressure and test standard

• Maximum differential pressure, leak rate class, and test procedure.

Hardware details

• Groove dimensions, surface roughness, metallurgy, and coating.

Motion type

• Static, slow rotation, oscillation, or linear stroke.

Industry standards

• API, ISO, EN, or company internal specifications.

With this information we can match seal design, material set, and spring type.

We can also advise on hardware adjustments to improve PV performance and safety margin.

FAQ 

Q1. Where are cryogenic seals used most often?

Cryogenic seals are common in LNG plants, truck and ship loading systems, industrial gas filling stations, air separation units, and research cryostats.

If a system handles liquid gas below 0 °C, it likely needs one or more cryogenic seals.

Q2. Why do you use spring energized designs instead of normal O-rings?

Standard elastomer O-rings lose elasticity at very low temperature.

A spring energized seal keeps a constant mechanical load on the sealing lips.

The spring plus media pressure gives much more stable sealing over temperature cycles.

Q3. Can one seal cover both cryogenic and ambient service?

Often yes, but it needs careful design.

We choose materials and geometry that stay flexible at low temperature but also resist wear at ambient.

In some critical valves, we use a combination of seals to cover the full range safely.

Q4. What information do you need to recommend a cryogenic seal?

Basic data is enough to start: medium, temperature range, pressure, valve or pump type, and approximate sizes.

If you can share drawings or photos, our engineers can respond with a more precise proposal.

Q5. How do your products differ from a generic cryogenic seal manufacturer?

Unlike standard distributors, we are not limited to catalog parts.

We design and machine custom spring energized seals, ball valve seats, stem seals, and piston seals to match your hardware.

We also support small batches for retrofit projects and field upgrades.

Talk to Our Engineering Team

If you are planning a new LNG or industrial gas project, we can help you choose the right cryogenic seals from the start.

Send us your working conditions and any available drawings.

Our team will review the case, propose a seal design, and suggest hardware changes if needed.

Need support from an experienced cryogenic seal manufacturer?

You can reach our engineering team by email xhh@xhh-smartech.com, share your operating data, and request sample seals or a trial kit for your next shutdown.