By Murray Corporation on May 7, 2019 9:00:00 AM
Stainless steel is an alloy that is resistant to most types of corrosion, including “red rust.” It is an ideal material for making hose clamps that will stand up to the requirements of your job.
But stainless steel comes in a wide variety of types and grades (and with an equally wide variety of price tags), so it’s challenging to know which grade of stainless steel is best for your particular job. Understanding what stainless steel is and how it performs will help you find the right clamp.
These five tips will help you as you compare clamp manufacturers.
Steel By The Numbers
Steel is an alloy of iron and carbon. Add chromium to the mix, and you get stainless steel, which comes in various grades based on different proportions of these three ingredients. In addition, many grades also include other elements, such as nickel, manganese, and molybdenum. These other elements will change the performance of the stainless steel.
Instead of names, the different grades of stainless steel are identified by numbers, which refer to the formulas used to make them. These numbers were originally given by the AISI (American Iron and Steel Institute), an industry group, and the SAE (Society of Automotive Engineers), a professional group. Today many standard stainless compositions are known by three-digit AISI numbers, or “nicknames.”
These nicknames are given to refer to several basic types of alloys. In each, the first number refers to the overall group that the individual grade is part of:
- 1XX: lean alloy stainless steels
- 2XX: nickel-chromium austenitic stainless steels
- 3XX: higher nickel-chromium austenitic stainless steels
- 4XX: martensitic and ferritic stainless steels
The other two digits reflect the proportion of the other ingredients in the alloy. Unless you’re a metallurgist, though, you probably don’t need to know the specific chemical formulas of, say, 304 versus 316 stainless steel.
What you do need to know is that each of these formulas has a certain amount of leeway built into it; the AISI and SAE standards specify a range for each ingredient. For instance, 301 stainless steel, a nickel-chromium alloy, is made up of six primary elements. For each element the required amount is specified as a percentage range, such as 6% to 8% for nickel.
So an actual piece of 301 stainless steel will differ slightly from manufacturer to manufacturer, and even from batch to batch by a single manufacturer. Any individual piece might be at the low end of the acceptable range for nickel. In that case, it will be certifiable as 301 stainless steel, but it may not perform the same as a piece with a higher nickel content. And since each of the other five elements also has an acceptable range, quality and performance can vary significantly between two samples.
It’s thus essential to find a supplier you can trust to provide a quality of steel that will meet your standards.
Picking For Performance
In general, the lower the AISI number, the less expensive the steel. Price isn’t the only issue, though: Other attributes also vary according to the grade.
Chromium is what makes stainless steel “stainless”; it creates a “self-healing” oxide film that resists rust under normal circumstances. That film forms when stainless steel is cut, so the rust-resistance is a characteristic of the material itself, unlike a surface coat of another metal or paint. All stainless steels provide a baseline level of rust resistance.
In addition, there are other kinds of corrosion, as well as environments that are more challenging. Other ingredients beyond chromium can be added to the steel to meet these challenges. For instance, molybdenum, an ingredient in 316 steel, improves corrosion resistance in environments with higher levels of salt and chloride, such as seaside areas or heavily salted roadways.
Certain applications call for clamps with high relative strength that will hold up to high pressures or temperatures – or both – so they don’t bend. Such an application could call for a clamp made from one of the 4XX stainless grades.
Ductility refers specifically to the quality of a metal that makes it capable of being drawn out into a wire, but more generally ductility means the quality of being shapeable – it’s the amount of “give” in a metal. For some applications, ductility can be an advantage.
For instance, in a pinch clamp, the clamp has to be applied over a fitting and a hose, each of which might be slightly bigger or smaller than the stated size and still be within specs. Part of that compensation is the ductility of the metal used in the clamp, which needs to be applied with a tight fit despite the actual sizes of the fitting and hose.
Despite stainless steel’s reputation for being non-magnetic, some grades may show slight degrees of magnetism and still be legitimately stainless. But for certain highly technical applications, even a slight level of magnetism may be unacceptable. In this case, you’d want a clamp made of 316 stainless steel.
Sometimes you need to be able to weld the clamp to other components in your installation. Welding stainless steel requires not only specific techniques, but the right kind of stainless steel. Check with your supplier to make sure the clamp you’re considering will lend itself to being welded.
The various grades of stainless steel each have different chemical compositions and different characteristics. If that didn’t make things complicated enough, sometimes a clamp will be made using different grades in different components, such as the band and the housing in a stainless steel worm drive. Add in the various coatings that can be added for lubrication or additional corrosion resistance, and the choices can seem overwhelming.
Your supplier will be able to provide additional information about choosing the best stainless steel clamp for your needs from among the standard options, or for having a custom clamp designed and manufactured if necessary.