The Penflex Hose and Braid Product Catalog lists the maximum pressures for hose assemblies “at 70 °F”.  What if I have a temperature which is much lower?

As temperatures increase above 70°F, the ultimate tensile strength of stainless steel decreases.  As temperatures decrease, the ultimate tensile strength actually increases.  The information below describes the properties of austenitic stainless steels (All of the stainless steels in the 300 series, like 304, 321 and 316L are austenitic stainless steels) in very low temperatures.

Generally speaking, the austinetic stainless steel, as used in corrugated metal hose, is suitable for applications to the lowest temperatures encountered in cryogenic applications.  “Austenitic stainless steels have been used extensively for subzero applications to -269°C (-452°F). The tensile strengths of chromium-nickel austinetic stainless steel increases markedly with decreasing temperature; yield strengths also increase but to a lesser degree. Correspondingly, there is some reduction in ductility as measured by elongation and reduction in area, but ductility values remain high down to the lowest temperature for which data is available. These steels also retain good toughness at -260°C (-452°F).” (1) The fatigue strengths of 300 series stainless steels actually increases as the operating temperature decreases. There is a corresponding decrease in the fatigue, crack growth rates.

In a corrugated metal hose application as the temperature decreases, the following occurs:

• The strength of the hose increases.
• The resistance of the hose to initiation of fatigue cracks increases.
• Fatigue cracks, which are present, or originate, progress through the hose wall at slower rate than at room temperature.

In designing a metal hose assembly for cryogenic service, care must be taken to insure that the fittings and any accessory (guard/liner) materials are suitable for the intended operating temperatures.

Ref: “Stainless Steels” Dec. 1994 American Society for Materials