Max service temp. (practical meaning)

[321GO]

Hi guys, hope all is dandy.

What exactly does "max. service temp" mean for a material?

It seems pretty straightforward but I'm not sure.

 

[arunmrao]

I would define it as the safe operating temperature, at which the material can perform without losing its form, chemical and physical properties.

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[321GO]

Thanks arunmrao. The term kind is kind of misleading I think since it sort of implies that properties are stable up to that temp (which clearly is not the case, for instance tensile strenght reduction).

Is this directly related to not upsetting the original lattice (previous heat treatments / alloying)?

 

[mrfailure]

Even operating within the max service temperatures range, you will see degradation of materials in elevated service over time (For example, alloy & carbon steel steam piping and boiler tubing will see carbon spheroidize at elevated temperatures). Besides temperature, you need to be operating within the maximum allowable stresses at those temperatures as outlined in the ASME BP&V Code.

 

[MagBen]

unless there are some specific area, and specific materials where make this term being a specific meaning, it indicates the max temeprature at which a material can be used in applications/engineering. Strength can be decreased to the extend that it is still meet the spec. For example, suppose a spec. asks for a min strenght 50ksi, a material yields 100ksi, the material is still usable when strength decreases with temperature down 40% of strength to 60ksi.

 

[metengr]

It typically means the "safe" use temperature for materials, at least for ASME B&PV Code and most other codes.

 

[moltenmetal]

Often the "safe" maximum operating temperature implies some period of use. If the period of use can be safely reduced, the maximum temperature can be higher. In boiler/pressure vessel and piping codes, the duration considered is on the order of 100,000 hours.

 

[tbuelna]

It also depends on the type of material being considered. For example, some plastics might experience significant creep or relaxation at very modest temperatures. While some carburized alloy steels might experience loss of temper at temperatures much beyond 350degF, other case hardened alloy steels can safely operate at temps of over 600degF.

 

[321GO]

"unless there are some specific area, and specific materials where make this term being a specific meaning, it indicates the max temeprature at which a material can be used in applications/engineering. Strength can be decreased to the extend that it is still meet the spec. For example, suppose a spec. asks for a min strenght 50ksi, a material yields 100ksi, the material is still usable when strength decreases with temperature down 40% of strength to 60ksi."

Thanks for the response all. I still find this this a tricky phrase. 'Perhaps' it may indicate that the under Tmax certain heat treatments / alloying properties are not effected but still there is degradation in thensile strength regardless, as also pointed out above.

If I'll ever run in to this I'll sure give it some second thoughts just to be sure.

 

[rconner]

I agree this is a potentially somewhat "tricky" question. In addition to the good responses of others, if the "material" happens to be used for something that conveys or otherwise comes into contact e.g. with food products or potable water, it is known e.g. that elevated temperatures accelerate some leaching of potentially harmful substances (i.e. "bad actors") from some materials into the previously potable water etc. In such cases, one must therefore watch what testing/temperature rating the material has per certification e.g. to NSF-61 and standard (for potable water) etc.

 

[tbuelna]

To answer the specific question posed in OP, the term "max. service temp. for a material" has no meaning without additional context. For example, PTFE can handle exposure to temperatures above 400degF. But even at room temperature PTFE will still cold flow when subjected to modest sustained pressures.