Posted on November 30, 2021

Material Selection Mistakes Can Lead to Disaster

John Joyce
Written by

John Joyce

Posted in
Hydraulic Safety

It’s important to find material that best fits your hydraulic system to ensure safe operation and superior performance. Many factors must be understood before selecting, and those include structural, material properties and environmental impact.

Understanding your overall design and structure

While choosing the right material is important, you must first understand the design of the system and the environment it is operating in. These factors will help you to select the types of hydraulic fittings needed for the system and the proper alloys for those fittings. You’ll look at the functionality and environment to determine the correct material to enable the design.

By looking at both physical and mechanical properties, you’ll be able to determine if the material fits the design specifications. Consider characteristics like chemical composition and internal structure. Here are some other common properties:

  • Conductivity
  • Corrosion resistance
  • Density
  • Ductility/malleability
  • Elasticity/stiffness
  • Fracture toughness
  • Hardness
  • Plasticity
  • Strength, fatigue, shear, tensile, yield
  • Toughness
  • Wear resistance

Material selection is an important process in fulfilling the design. The material section can be either revolutionary or evolutionary. Revolutionary means it’s pertaining to a new material while evolutionary means an older, slightly modified material. Typically, alloy choices fall into the evolutionary category because there is less risk.

Learning lessons from the space shuttle tragedy

The 1986 Space Shuttle Challenger happened because of an O-ring failure, causing seven astronauts to lose their lives. Temperatures were below freezing at Cape Canaveral, Florida, that day. It was the coldest launch in NASA’s history. This cold temperature is what caused the material of the O-ring to lose its flexibility; so, it moved slower and allowed gases to flow through the gap, breaking the seal of the fitting.

As a result, the O-ring failure allowed burning rocket fuel to leak from the side of the booster. This heat then melted booster-attached hardware, which caused the back portion to become disconnected. This is what ultimately caused the rupture of the already weakened external tank.

Reviewing the application and potential environmental impact

The temperature of the environment impacts hydraulic system operation, so that should determine material selection. Depending on the temperature, a metal-to-metal seal may be necessary, which is why you must understand the operating environment and your application.

The Space Shuttle Challenger disaster was a fatal accident that could have been avoided if the environment was considered during material selection. An O-ring is made from rubber and is used for lots of different sealing applications.

A space shuttle launch includes lots of high pressure, and it typically causes the O-ring to flex slightly. But since the weather was very cold that morning, the O-ring did not flex like it should for those high-pressure applications.

Also, if the application has the potential for high corrosion, stainless steel or even brass might be the best solution when looking at alloys. Common heavy equipment and industrial applications require carbon steel and usually need a zinc electroplated coating to resist corrosion.

Extending the life of a hydraulic system

In conclusion, the material selection process should not be taken lightly. The type of material used will determine if the system has adequate strength and corrosion resistance to safely handle the high pressure. The safety, reliability and service life of a hydraulic system are only as good as its transfer lines and connections.

Selecting the right material is critical, and the STAMP method has become an industry-wide term for selecting fluid and gas components within the design. Learn more about how to choose the right fittings for your application by downloading our white paper on “The What, Where and Why of Tube Fittings and Adapters.” The white paper reviews the STAMP method and much more.

Get Your Copy of The Tube Fittings & Adapter Whitepaper

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