indispensable. One such material is Invar Plate—a nickel-iron alloy celebrated for its exceptionally low coefficient of thermal expansion (CTE). This property makes it particularly valuable in cryogenic equipment, where temperature changes can cause materials to contract, expand, and potentially compromise performance.
If you’re designing or sourcing components for cryogenic systems, selecting the right Invar Plate can significantly improve operational reliability, reduce downtime, and maintain dimensional accuracy. This blog explores the key considerations for choosing the most suitable Invar plate for your application.
What Is Invar Plate?
Invar, short for “invariable,” is a nickel-iron alloy typically composed of 36% nickel and 64% iron. It is widely used in environments that require minimal expansion or contraction under temperature variations.
When formed into plates, Invar becomes an ideal structural material for applications involving tight tolerances and extreme temperatures—particularly in cryogenics, aerospace, electronics, and tooling.
Key Characteristics of Invar Plate:
- Extremely low thermal expansion (around 1.2 x 10⁻⁶/°C at room temperature)
- Excellent dimensional stability in both high and low temperature ranges
- Good machinability and weldability
- High strength and toughness at cryogenic temperatures
Why Invar Plate Is Preferred in Cryogenic Equipment
Cryogenic systems—such as those used in liquefied natural gas (LNG) storage, MRI machines, superconducting magnets, or scientific instruments—operate at temperatures as low as -196°C. Most metals shrink or deform significantly under such conditions. However, Invar Plate resists dimensional change, which helps maintain structural integrity and performance.
Applications in Cryogenic Systems:
- Vacuum chamber walls
- Internal supports and brackets
- Sensor mounts and alignment frames
- Insulation support in cryo tanks
- Components in superconducting electronics
Factors to Consider When Choosing Invar Plate for Cryogenics
Not all Invar Plates are created equal. Selection depends on various parameters, including application demands, temperature range, mechanical stress, and manufacturing processes. Here’s what to evaluate:
1. Thermal Expansion Requirements
The main reason Invar is used in cryogenics is its low thermal expansion. Confirm the exact coefficient of thermal expansion (CTE) required for your design. Standard Invar has a CTE of ~1.2 ppm/°C, but certain conditions (e.g., cryogenic exposure, post-processing) may impact performance.
Tip:
Look for material tested for thermal behavior below -150°C or even -196°C (liquid nitrogen temperatures) to ensure compatibility.
2. Material Certification and Standards
Ensure the Invar Plate complies with international standards like:
- ASTM F1684 – for general Invar alloy plates and sheets
- ASTM B753 – for flat-rolled Invar materials
- AMS I230 – for aerospace-grade Invar
Certified material guarantees consistent quality and traceability—critical for regulated sectors like aerospace, medical, and scientific research.
3. Thickness and Flatness Tolerances
For cryogenic support structures, tight tolerances are a must. When selecting Invar plate:
- Specify required thickness range (commonly from 0.5 mm to 50 mm)
- Define flatness requirements (e.g., ≤0.1 mm/meter)
- Ask your supplier about their precision milling or grinding capabilities to achieve those tolerances.
4. Annealed vs. Cold Rolled Condition
Invar can be supplied in various conditions:
- Annealed Invar Plate: Soft and ductile, easier to machine or weld.
- Cold Rolled Invar Plate: Stronger, but may retain internal stresses unless stress-relieved.
For cryogenic applications, annealed plates are often preferred to prevent warping during temperature cycling.
5. Machinability and Weldability
Cryogenic equipment often requires precise machining and sometimes custom welding. Choose Invar plates that:
- Are machinable with carbide tools
- Can be welded using TIG/MIG methods with matching Invar filler rods
- Have undergone appropriate surface treatment (pickling, cleaning, or electropolishing)
This ensures compatibility with downstream fabrication or assembly.
6. Supplier Capabilities and Customization
Work with a supplier who understands cryogenic-grade Invar and offers:
- Custom-cut plate sizes
- CNC machining
- Surface finishing
- Ultrasonic or dye penetrant testing
- Just-in-time delivery for critical projects
Some suppliers even provide pre-machined Invar components tailored to your application, which can save engineering time and reduce scrap.
Example: Invar Plate in an LNG Storage Application
A common use of Invar Plate is in supporting structures inside LNG cryogenic tanks. These internal frames must stay dimensionally stable while exposed to temperatures nearing -160°C. A poorly selected material might shrink unevenly, leading to thermal stress and structural failure.
By using Invar plates with certified CTE values and precise flatness tolerances, engineers can:
- Maintain tank integrity
- Reduce risk of mechanical fatigue
- Improve long-term reliability and safety
Sustainability and Long-Term Performance
Though Invar is more expensive than traditional stainless steel or aluminum, it offers lifespan and performance advantages that justify its use. With fewer replacements, less maintenance, and better operational consistency, it proves to be a cost-effective solution over time.
Additionally, many Invar Plate suppliers offer recycled material options or buyback programs for offcuts, aligning with sustainable procurement practices.
Final Thoughts
Choosing the right Invar Plate for your cryogenic application is not just about thermal stability—it’s about ensuring every component performs reliably under the most demanding conditions. From plate thickness and CTE to machining requirements and supplier credibility, every detail matters.
When sourced correctly and engineered with precision, Invar Plate can elevate the safety, performance, and longevity of your cryogenic systems.
