Understanding the Low Magnetic Permeability Requirement
For applications in nuclear power, MRI systems, particle accelerators, superconducting equipment, semiconductor manufacturing, and other precision industries, 316LN stainless steel plates are often required to have a relative magnetic permeability (μr) of no more than 1.04. This stringent specification ensures that the material remains essentially non-magnetic and does not interfere with sensitive magnetic fields or precision instruments.
At SSMALLOYS, we supply high-quality ASTM A240 316LN stainless steel plates with controlled magnetic permeability, certified testing, and full material traceability for demanding industrial applications.
What Does "Relative Magnetic Permeability ≤ 1.04" Mean?
Relative magnetic permeability (μr) measures how easily a material can be magnetized compared to a vacuum.
- μr = 1.0 indicates a completely non-magnetic material.
- μr ≤ 1.04 means the material remains essentially non-magnetic, with only a very slight magnetic response.
Although 316LN is an austenitic stainless steel, excessive cold working or improper processing can introduce magnetic phases, increasing the material’s permeability. Therefore, many critical projects specify a maximum magnetic permeability of 1.04 or even lower.
Why Is Magnetic Permeability Important?
Low magnetic permeability is essential in applications where magnetic interference could affect equipment performance or measurement accuracy.
Typical industries include:
- Nuclear Power Plants
- MRI (Magnetic Resonance Imaging) Equipment
- Particle Accelerators
- Superconducting Magnet Systems
- Semiconductor Manufacturing
- Scientific Research Facilities
- Lucht- en ruimtevaart en defensie
- Cryogenic Equipment
Maintaining a low magnetic permeability helps ensure stable magnetic fields, improved measurement accuracy, and reliable equipment performance.
Why Choose 316LN Stainless Steel?
Compared with conventional 316L stainless steel, 316LN contains a controlled addition of nitrogen, which provides several advantages:
- Higher yield strength
- Improved tensile strength
- Uitstekende corrosiebestendigheid
- Superior low-temperature toughness
- Better resistance to strain-induced martensite
- Lower magnetic permeability after fabrication
Because nitrogen stabilizes the austenitic structure, 316LN is less likely to become magnetic during manufacturing and forming operations.
Factors Affecting Magnetic Permeability
Although annealed 316LN is essentially non-magnetic, several factors may increase its magnetic permeability:
- Cold rolling
- Cold bending
- Bewerking
- Stamping
- Lassen
- Excessive plastic deformation
These processes can produce strain-induced martensite, resulting in higher magnetic permeability.
To maintain μr ≤ 1.04, manufacturers should carefully control fabrication procedures and minimize cold work whenever possible.
Typical Magnetic Permeability Values
| Materiële toestand | Typical Relative Magnetic Permeability (μr) |
| Solution Annealed 316LN | 1.00 – 1.02 |
| Light Cold Work | 1.02 – 1.04 |
| Moderate Cold Work | 1.05 – 1.15 |
| Heavy Cold Work | Above 1.20 |
Actual values depend on the manufacturing process and testing conditions.
How Is Low Magnetic Permeability Achieved?
To satisfy stringent project requirements, manufacturers typically employ:
- Oplossingsgloeien
- Rapid Water Quenching
- Controlled Cold Working
- Strict Process Control
- Final Magnetic Permeability Testing
These measures help maintain a stable austenitic microstructure and minimize the formation of magnetic phases.
Magnetic Permeability Testing
Magnetic permeability is typically measured using specialized instruments such as:
- Fischer FERITSCOPE®
- Severn Permeability Indicator
- Other calibrated permeability meters
Testing may be performed according to customer specifications or internationally recognized methods, such as:
- ASTM A342
- IEC 60404 Series
- Project-specific testing procedures
The measured value is usually included in the inspection documentation when specified.
Typical Purchase Specification
A common technical requirement may be written as:
Materiaal: ASTM A240 Type 316LN Stainless Steel Plate
Warmtebehandeling: Oplossing gegloeid
Relative Magnetic Permeability: μr ≤ 1.04
Testen: ASTM A342, IEC 60404, or approved equivalent
Certification: EN 10204 3.1 Material Test Certificate including Magnetic Permeability Test Report
FAQs About how to select the right carbon steel flange
No. Fully solution-annealed 316LN is essentially non-magnetic, but slight magnetism may develop after cold working or fabrication. For critical applications, a maximum relative magnetic permeability (such as μr ≤ 1.04) is often specified.
The addition of nitrogen in 316LN improves strength and stabilizes the austenitic structure, making it less susceptible to strain-induced martensite and helping maintain lower magnetic permeability after fabrication.
No. ASTM A240 specifies the chemical composition and mechanical properties of 316LN stainless steel but does not define a magnetic permeability limit. Requirements such as μr ≤ 1.04 are typically project-specific specifications requested by the end user.
It is measured using calibrated magnetic permeability instruments, and the results can be included in the Material Test Certificate (MTC) or a separate Magnetic Permeability Test Report upon request.
Full-service supplier of Stainless Steel Plate for all your requirements
SSM offers significant product advantages in the manufacture of Stainless Steel Plate. Whether it’s quality or price – we will meet your requirements.
Trusted Stainless Steel Plate Manufacturer & Supplier
SSMALLOYS supplies premium 316LN stainless steel plates for industries requiring exceptional corrosion resistance, mechanical strength, and low magnetic permeability.
Our capabilities include:
- ASTM A240 316LN Stainless Steel Plates
- Controlled Magnetic Permeability (μr ≤ 1.04 upon request)
- Solution Annealed Material
- EN 10204 3.1 / 3.2 Certification
- PMI Testing
- Magnetic Permeability Testing
- Ultrasonic Testing (UT)
- Third-Party Inspection (SGS, BV, TÜV, DNV)
- Worldwide Delivery
Whether your project is for nuclear power, MRI equipment, semiconductor manufacturing, or scientific research, SSMALLOYS provides reliable stainless steel materials that meet demanding technical specifications.
Looking for a trusted Stainless steel Plate manufacturer?
Whether you need standard stainless steel plates or high-performance alloy materials for demanding industrial applications, SSMALLOYS is your reliable manufacturing and supply partner. We provide a comprehensive range of stainless steel plates, sheets, coils, and strips in accordance with international standards, serving customers in the oil & gas, chemical processing, power generation, marine, food processing, pharmaceutical, and construction industries.
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