It comes as no surprise that metal hose is the preferred choice for high-temperature applications. But what about low-temperature applications? This is a question frequently seen from customers. The simple answer is yes- metal hose is a great option for low-temperature applications. However, there are important factors that should be considered before making a recommendation.
Before recommending a particular metal hose for a low-temperature application, the conditions that the hose will experience while in service should be identified. For example, what are the minimum and maximum temperatures of the application? If the assembly is going to be exposed to wide temperature variances, it is important to determine how frequently and rapidly the temperature will change. Metals expand and contract as they heat and cool, and they do so at different rates depending on the alloy.
Severe fluctuations in operating temperature can apply stress on welded joints as the base materials expand and contract, which may cause cracks to form.
One way to verify that an assembly will be able to accommodate these stresses safely is by conducting a “cold shock” test. Cold shock (aka “thermal shock”) testing is performed by plunging an assembly into a cryogenic bath, then allowing it to return to room temperature (or to the highest temperature to which it will be exposed), followed by various testing and inspection. This ensures that the welds will not crack when exposed to similar temperature extremes while in service.
Another service condition to identify is whether the temperature extremes will be present inside the metal hose (the media temperature) or outside the hose (the external environment). Will the hose be buried in ice? Will it have cryogenic liquids flowing through it? Is there a chance the media could freeze and change into a solid? Is it possible for frost to build-up on the hose exterior? These are all potentially damaging conditions that can be mitigated by selecting the correct assembly for the job.
For example, an application in which the metal hose may surrounded by a cold exterior environment may be best served by utilizing a traced assembly. It’s often recommended to use the STAMPED acronym to assist in identifying the service conditions for any hose application.
Standards and Certifications
Along with service conditions, it is important to also identify any standards that must be met in an application. This can be a challenge because there are different standards that may apply depending on the alloy, the forming process (cast, forged, drawn, etc.) and the finished product (hose, pipe, flanges, etc.).
Hose Master uses the low temperature ratings in the ASME Process Piping Code B31.3, as well as other internationally recognized standards. Identifying the applicable standard is important because different standards may have different low temperature ratings for the same alloy.
When identifying standards, it is also important to note that a particular alloy may have multiple certifications, meaning it complies with two (or more) standards, each of which may offer different ratings for a given alloy. For example, many of our alloys comply with both ASTM and EN (European) specifications. In these instances, the standard specified by the customer dictates the minimum allowable temperature rating.
Finally, the method of fabrication may affect the allowable low temperature limits. Many standards include or make reference to various welding requirements, many of which require the welders to achieve and maintain compliance to those standards through thorough education, testing, and audits. These standards may dictate the allowable low-temperature limits for a welder’s certification, superseding the low-temperature limits of the materials being joined.
Selecting a Metal Hose for a Low-Temperature Application
In summary, there is no one answer to “how low you can go” in regards to operating temperatures for metal hose. Finding out as much as possible about the intended application, including any applicable standards, ensures not only that the materials of the assembly will be able to handle the application, but also that the assembly will conform to any required specifications.
The original article was written by Abby Svitana, Market Analyst at Hose Master.
Gallagher Fluid Seals is an authorized distributor of Hose Master. For more information about Hose Master products or if you have a custom engineering need, please contact Gallagher Fluid Seals.