What Is Air Aging, and Why Do I Care?

This is the fifth installment of our “Why Do I Care” series. Every so often, we’ll blog about some of the questions people new to the gasket industry may be looking for more information about. Click the links below to read the first four installments:

What Is Compressibility & Recovery, and Why Do I Care?

 What Is Bolt Load, and Why Do I Care?

 What Is Creep Relaxation, and Why Do I Care?

 What Is Ignition Loss, and Why Do I Care?

This week, we’re going to talk about air aging as it relates to your gaskets and gasket material, and why it is important. Air aging is similar to ignition loss in the fact that there is interest in the weight loss of a material at elevated temperatures, but the similarities really stop there. So, what is air aging?

Air Aging

The purpose of air aging is to observe both the weight change and the change in thickness of a finished material. If the test is done per ASTM D-573, the material is typically placed in a furnace for 70 hours at 1000°F. However, you could also test at a temperature that is of particular interest to your application. In general, the intent is to determine how the material retains its properties after temperature exposure. As you can imagine, some materials will dry out and get brittle when exposed to heat. This is the intent of the test, to verify in a basic format, if the material is acceptable for the joint chosen. The tests for indicators for this can include: weight change, thickness change, compressibility, recovery, flexibility, and delamination depending on the material. Data points are gathered before and after to determine the change. The material or application engineer can then decide if the material is adequate for the gasket.

Sometimes, you don’t even need data to tell that a material did not perform well in the test. Here are two actual pictures from an air aging test recently performed in our lab. The material on the left is a competitor’s, and you can see how all of the layers have separated as a result of the heat. The material on the right is a Metal Tech grade.  It is clear that it has retained its integrity and not peeled apart or delaminated when subjected to the same heat.

Air Aging

What To Do With It

As with any lab test, it is important to remember that the results that you obtain in a laboratory environment are not necessarily what you will see in the actual application, but they are a pretty good indication of whether or not you are on the right track with a material. The better a material performs in a lab, the higher level of confidence you will have of the performance in the application.

How much attention do you pay to air aging results?

Hi-Tex product comparison

The Great Gasket Debate: To Reuse or Not To Reuse

To reuse or not to reuse gasket material…that is the question. Depending on who you ask, you will almost always get differing answers and advice. Those people that are cost conscious will almost always recommend to reuse every gasket you can. (“There’s still more life in it!”) Those that are strictly focused on performance will always tell you to never reuse a gasket. (“Once you break the seal, you will never achieve the same level of performance!”)

As a trusted gasket material supplier, our recommendation is that you never reuse a gasket. (Ok, ok, we know you are probably thinking “of course they would say that…they just want to sell more material” – but hang with us on this one.) As an expert resource that knows gasket material inside and out, we’re going to break down some of the arguments for and against reusing, and what you need to consider when making that decision for your application. And maybe…there is a time or two that it really might be ok to reuse one.

Reusing a Gasket

If you’ve never been told, you’ve likely always wondered if that gasket could be reused. “It still looks ok, I wasn’t having any problems with it…I wonder if I could throw it back on there??” Here are some of the common arguments for reusing a gasket, and some situations where it might work to reuse.

  1. If the gasket hasn’t seen heat exposure yet of an operating unit, it might be ok to reuse.
  2. If the gasket hasn’t seen fluid exposure and swelling of an operating unit, it might be ok to reuse.
  3. “It looks ok” is more of a subjective approach, but might indicate that the gasket is still ok to use as long as the initial thickness is still correct and it has sufficient compressibility left in it to achieve a seal.

Replacing a Gasket

There are many people out there that would never replace a gasket. How does one really know if it is going to work the same way twice? Here are some of the common arguments for never reusing a gasket.

  1. Heat exposure: Exposure to elevated temperatures causes materials to deteriorate. Sometimes this means: dry out, stiffen up, saturate, get brittle, take a set, etc. Once this seal has “seated” in the application, it should not be disturbed. A new gasket is required to go through the initial seating phase and achieve a proper seal.
  2. Fluid saturation: Exposure to fluids sometimes causes materials to swell, impregnate, or saturate. In a seal situation, this often helps to create the seal. Reusing a gasket is not advised as the saturation and absorbancy condition can vary. A gasket should be assembled, then exposed to heat and fluid. A used gasket already having swelling due to the fluids should not be reused.
  3. Compression set: The third reason not to reuse a gasket is related to the first two. Once a gasket has taken a set (due to temperature and fluids), it should not be disturbed or reused. It would not have the same properties available to go through the initial compression provided by the joint and achieve the initial seal.

Our Recommendation

Like we’ve mentioned, our official position is to never reuse a gasket. As a gasket material manufacturer, we run our tests and certify our products when our material is at 100%. We know for a fact that our material can handle the conditions it is specified for IF the gasket (and joint) is designed properly, and installed correctly. What we don’t know is how our material will work after the seal has been disturbed or disassembled. It may work just fine, it may have been damaged in the process – we don’t know, and it would be impossible to test in enough conditions to enable us to come to a strong conclusion that we would have any confidence in.

We take pride in the quality and the performance of our material (as do many others), and we don’t believe the risk of damage to your application is worth the reward of saving a few dollars from reusing a gasket.

Replace to be safe!

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