By: Frank Caprio | On: February 10, 2017
Metal hose for low temperature applications?
It is well known in our industry that metal corrugated hose is the preferred choice for applications where high temperatures are present, but we are often asked about using metal hose for low temperature applications. The quick, easy answer is “sure it can be used!” However, there are important factors which should be considered before making a recommendation.
The first step is to define the intended service conditions. What are the minimum and maximum temperatures of the application? If the assembly is exposed to wide temperature variances, determine how frequently and rapidly the temperature changes. Metals expand and contract as they heat and cool, and at different rates depending on the alloy. Severe changes in operating temperature can apply significant stresses 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 (or “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.
Also, identify if the temperature extremes are present inside the 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 any chance the media can freeze and change into a solid? What about frost build-up on the hose exterior? These are all potentially damaging conditions that must be dealt with. We recommend using the STAMPED acronym to assist you in identifying the service conditions for any hose application.
Secondly, define what standards (if any) must be met. This can be difficult, 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 very important, because different standards may have different low temperature ratings for the same alloy.
To complicate things further, a certain 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 raw materials 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, audits, etc. These standards may dictate the allowable low-temperature limits for a welder’s certification, superseding the low-temperature limits of the materials being joined.
In summary, there is no one answer to “how low can you go?” Finding out as much 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. If you have any further questions, please do not hesitate to contact Hose Master’s Inside Sales team or call us at 800-221-2319.
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