Cryogenic Testing
What Is Cryogenic And Cold Shock Testing, And What Is It Used For?

You may have heard of cryogenics – the process of producing extremely low temperatures to discover its effects on a test subject. Chances are, though, you associate it more with science fiction than real life.

But cryogenics is real. In fact, it’s one of the testing services we offer at Precision Fabrication and Cleaning (PFC).

What is cryogenic and cold shock testing used for? And what exactly does this test measure? In this article, we’ll answer both questions.

What Is Cryogenic And Cold Shock Testing?

To understand cryogenic and cold shock testing, we must first define the word “cryogenic” in terms of temperature.

Cryogenic temperature is the temperature at which molecular motion comes as close as theoretically possible to completely stopping. It is defined as anywhere between -238 degrees Fahrenheit and absolute zero, which is -460 degrees F. The latter is the temperature at which a thermodynamic system has the lowest amount of energy. In other words, this is the current scientific standard for the lowest temperature in existence.

By quickly lowering the temperature of an object, such as piping or fittings, to cryogenic temperature, we expose the object to cold shock. Our object with this type of test is to make sure that the object will hold up against extremely low temperatures without cracking, disintegrating, or showing any other signs of internal or external damage.

To start the cold shock, we immerse the test object in a bath of liquid nitrogen. Certain substances, like nitrogen (N2), revert to a liquified state when they are cooled down enough. Nitrogen turns into its liquid form (LN2) at -320 degrees F.

About an hour after the test object is exposed to cold shock through LN2, we drain the LN2 and allow the part to warm up to ambient temperature. Once it’s warmed up, we check it to make sure the cold shock didn’t cause any damage.

Industry Standards For Cryogenic Testing

Testing of cryogenic components is typically performed in accordance with two industry standards: 54000-GT08 and 54000-GT12. Adhering to these ensures the test is performed safely and successfully.

54000-GT08 Testing Of Cylinder Operated Cryogenic Valve

This standard requires a 7-step testing procedure, outlined below.

  1. Proof test
  2. Cycling test
  3. External leak test valve assembly
  4. External leak test operator
  5. Internal leak test valve assembly
  6. Internal leak test operator
  7. Test cold – Maintain minimal helium flow through valve during cold soak

54000-GT12 Testing Of Cryogenic Check Valves

This standard for testing cryogenic check valves also involves 7 steps.

  1. Proof test
  2. Cycling test
  3. External leak test
  4. Internal leak test (warm)
  5. Test cold – Maintain minimal helium flow through valve during cold soak
  6. Repeat external leak test at ambient temperature

What Is Cryogenic And Cold Shock Testing Used For?

Just as we evaluate certain components for their ability to withstand high temperatures, at PFC we also test components that will be subjected to extreme cold. Such tests are necessary to ensure that these components will remain intact under harsh conditions. This way, we know they will continue to function properly and not endanger the lives of anyone working near them.

The test objects may include parts from NASA rockets, such as valves and fittings for cryogenic propellant tanks. These tanks are filled with propellant that is cooled down to a cryogenic temperature. The sub-cooling of these tanks is an important and effective method for lowering the lift-off mass of a launch vehicle, thus improving the performance of the rocket engine.

Dangers Of Cryogenic And Cold Shock Testing

It is critical to hire a professional company that adheres to industry standards for cryogenic and cold shock testing. This is because there are many dangers associated with cryogenics that can only be avoided by utilizing the proper PPE, equipment, and procedures. That kind of knowledge only comes with training and experience.

Below are some dangers of cryogenic and cold shock testing.

Over-Pressurization Of Containers And Systems

Relieving the pressure of cryogenic substances during cold shock tests is a common safety protocol that non-experts will not know about. This step must be taken, or else destruction and injury will follow.

Without adequate venting or pressure-relief devices on test containers, enormous pressures can build up on the inside. Cryogens such as LN2 boil as they sit in their storage vessels by absorbing heat energy from their much warmer surroundings. The gas boiling out of the liquid must escape or the pressure will increase. The immense pressure can cause an explosion called a boiling liquid expanding vapor explosion (BLEVE).

The expansion ratio for liquid nitrogen to gas is approximately 1:700. This means that, as it vaporizes, the volume it occupies will expand close to 700 times. If liquid nitrogen is trapped inside a vessel, this expansion rate could cause an explosion from over-pressurization.

Asphyxiation

Air consists of 78% nitrogen and 21% oxygen, with trace gases making up the remaining 1%. Oxygen, in particular, is essential for humans to be able to breathe and for our blood to function properly.

Cryogens can create oxygen deficiency because they have large liquid-to-gas expansion ratios (generally >700). For example, one liter of liquid nitrogen vaporizes to 696 liters of nitrogen gas when warmed to room temperature.

Thus, a small liquid nitrogen spill produces a large volume of gas that can displace the air in a confined space, thus creating a serious oxygen deficiency. For anyone in the space who is not prepared and wearing the proper PPE, they may experience asphyxiation from the lack of oxygen. They could pass out or even die.

Oxygen Enrichment

While too little oxygen is dangerous, so is too much oxygen.

During the transfer of nitrogen through non-insulated metal pipes, the air surrounding the containment system may condense. Nitrogen, which has a lower boiling point than oxygen, will evaporate first. This can leave an oxygen enriched condensate on the surface that may increase the flammability (combustibility) of materials near the system, presenting all the same hazards as liquid oxygen. Many materials considered non-combustible could burn in the presence of liquid oxygen.

Extremely Cold Temperatures

Knowing the PPE protocols during cryogenic and cold shock tests, such as wearing goggles, a face shield, and an impervious coat and gloves, is critical to preventing injury and even death from exposure to cold temperatures.

As we already learned, cryogens are extremely cold. As such, they can cause instant, severe frostbite when they come into contact with human flesh. A jet of cryogen vapor can freeze the skin or eyes faster than liquid contact. Tissue damage may be extensive and possibly permanent, especially in the eyes.

Protecting the skin and sensitive tissues, such as the eyes, when near cryogenically cooled materials is also extremely important. Unprotected skin may adhere to metal that is cooled by cryogens and tear when you try to pull it away. Even non-metallic materials are dangerous to touch at low temperatures.

At cryogenic temperatures, many materials, such as rubber, plastic and carbon steel can become so brittle that they shatter. The resulting shards can cause injury to anyone standing in their vicinity. Only materials approved for use with cryogens should be used.

PFC Provides Safe Cryogenic And Cold Shock Testing

Cryogenic and cold shock testing is important to many industries, including space exploration programs like NASA. But, given that the tests require working with potentially dangerous cryogenic substances, we recommend you always hire professionals like PFC. This is the best way to ensure that the tests are performed according to industry standards of safety and quality. Contact us today.

About PFC: Precision Fabricating & Cleaning, is an innovative, highly-qualified company with unique capabilities to accomplish a wide range of industrial cleaning services, specializing in Hydrostatic Testing, Oxygen Cleaning Service, Cryogenic & Cold Shock Testing, Mobile Field Cleaning, Passivating/Passivation, High Purity Cleaning, Ultrasonic cleaning, and so much more.

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