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EnglishSevern Gage: Low Mu Permeability Indicator vs. Ferrite Indicator
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The Severn Gage comes in two models that measure different properties of weakly magnetic materials. The Low Mu Permeability Indicator measures magnetic permeability — how easily a material such as stainless steel can be magnetized. The Ferrite Indicator measures ferrite content, typically in stainless steel welds. Choose between them based on what you need to quantify: permeability of a base material, or ferrite content in a weld.
What each model measures
Low Mu Permeability Indicator
Permeability is a measure of a material's ability to be magnetized. This model is built for weakly magnetic materials such as stainless steel, where the permeability is low and small differences matter. If your question is "how magnetic is this material?", this is the model for the task.
Ferrite Indicator
This model measures the ferrite content of a material such as a stainless steel weld. Ferrite content in austenitic stainless steel welds is a common quality concern, and the instrument is used extensively to measure the soundness of welds in stainless steel pipes in nuclear power plants and food handling equipment.
The Ferrite Indicator is available in two calibration types:
- Percent Ferrite
- Ferrite Number
Choosing between the two
| Question you are answering | Model to use | Typical application |
|---|---|---|
| How magnetizable is this material? | Low Mu Permeability Indicator | Weakly magnetic materials such as stainless steel |
| How much ferrite is in this weld? | Ferrite Indicator | Stainless steel pipe welds, including nuclear power and food handling equipment |
The deciding factor is the property under test, not the material alone. Both models are aimed at weakly magnetic stainless steels, but one reports permeability and the other reports ferrite content.
A note on calibration
If you select the Ferrite Indicator, you also need to choose a calibration: Percent Ferrite or Ferrite Number. These are two different reporting scales, so match the calibration to the specification your inspection or acceptance criteria call for. The source material does not state which industries or standards prefer which scale, so confirm that against your own project requirements.
Practical context
The Severn Gage is described as a simple, rugged, non-destructive inspection instrument intended for laboratory, shop, and field use. That combination matters when the same measurement has to be repeatable across a lab bench, a fabrication shop, and an installed pipe in the field.
What the source does not cover
The available page material does not list pricing, ordering details, or full technical specifications for either model. If you need those, they would have to come from the manufacturer directly rather than from the product description summarized here.