Subject: Low Temperature Hose Service
By: Hose Master
Date: January 2008
One of the advantages metal hose has over rubber or plastic hose is the ability to withstand low (under 32°F /0°C) or
cryogenic (-150°C/-238°F) temperatures. However, it is still necessary to match the assembly components to the anticipated
application temperature. Many commonly used alloys such as carbon steel, turn brittle at or below -30°F. Fortunately, the
yield 1 and tensile 2 strengths of austenitic 3 stainless steels, nickel alloys such as 276, and many copper based alloys such as
bronze, significantly increase as the temperature decreases. The material ductility 4 decreases, but not sufficiently to preclude
their use for most applications.
The fatigue strength of 300-series stainless steels actually increases as the operating temperature decreases and there is a corresponding decrease in the fatigue crack growth rates. In 300-series stainless steel corrugated metal hose applications, as the temperature decreases:
- The strength of the hose increases
- The resistance of the hose to fatigue fracture initiation increases
- Fatigue cracks progress through the hose wall at reduced rates from those at ambient 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.
The European Standard BS EN 14585-1:2006 Pressurized Corrugated Metal Hose Assembly for Pressure Applications, Part 1: Requirements contains a guideline for the use of various alloys at two temperature limits (see Chart 1). For low temperature or cryogenic applications, all of the assembly components, including hose, braid, fittings, collars, weld material, and guard/liner must be of an applicable alloy.
| Chart 1 - Low Temperature Service Limits | |
|---|---|
| Down to -196°C/-321°F | Down to -270°C/-454°F |
| T304 | T304L |
| T316 | T321 |
| T316L | T316Ti |
| Copper based alloys | Nickel based alloys |
1) Occasionally the term "absolute zero" may be encountered. Absolute zero is -273.16°C/-459.7°F.
2) Any low temperature or cryogenic assemblies must be dried and capped to prevent any moisture ingress (including moist air).
3) "Austenitic stainless steels have been used extensively for subzero applications to -269°C (-452°F). The tensile strengths of chromium-nickel austenitic stainless steels increase 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 the above-mentioned temperatures." 5
1 Yield Strength is the point at which a stressed metal will not return to its original shape.
2 Tensile Strength is the maximum amount of pulling stress a metal can accommodate before failure.
3 Austenitic Stainless Steels include 300 series stainless steel (i.e. 304, 316 ...).
4 Ductility is the ability to form or change the shape of metal.
5 American Society for Metals International (1994). Stainless Steels. Ohio: ASM International® ISBN:0-87170-503-6
Reprinted with permission of ASM International®. All rights reserved. www.asminternational.org
Rev. A; Date: 1/28/08
T022 Location:s/procs/sales eng.
