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Minimum Design Metal Temperature Vs Minimum Design Temperature

Minimum Design Metal Temperature Vs Minimum Design Temperature

Hi All,

I need expert advise on following query:

In Piping Line Class Minimum Design Temperature is defined. Can We take the same valve for Minimum Design Metal Temperature of Piping Material of same Line Class.

Looking forward for valuable and useful response.

Thanks in advance.


RE: Minimum Design Metal Temperature Vs Minimum Design Temperature

As the minimum design metal temperature (MDMT) for the material is defined by the Code, the minimum design temperature (MDT) of the piping line class is based on the process condition, and applied for the pipe, fittings, as well as valves which are used in the piping class.

The MDMT could be the same or lower than the MDT.

RE: Minimum Design Metal Temperature Vs Minimum Design Temperature

Thanks for your useful response:

As mentioned in above response, MDMT is defined by code; Can anyone please confirm which code define this value. For more explanation of my query; for example As per ASME B31.3 table A-1;Minimum Temperature for Material API X65 has been referred to Curve A of Figure: 323.2.2A.
If pipe thickness in one line class is 40mm and MDT is 0 degree. C. As per Curve-A if this thickness of pipe are used at any temperature below 30 degree; Impact test is required. So can we assume that MDMT for API X65 with thickness 40mm is 30 degree C. Please confirm.

Also note that in this case;if this assumption is correct then MDT is lower than MDMT.

RE: Minimum Design Metal Temperature Vs Minimum Design Temperature

First, for the piping can be B31.3 (as in your example), for the vessel be ASME BPV Code. The MDMT may be different from one Code to the other.
Since the material MDT is lower than the MDMT, additional tests may be required per Code. Or, I may select a suitable material in the curve B without any testing as required per Curve A.

RE: Minimum Design Metal Temperature Vs Minimum Design Temperature

Since the valve has a pressure rating the MDMT would likely be limited the same as the pipe flanges, therefore it should be consistent with your piping. Have a look at Fig 323.2.2B for the maximum temperature reduction without impact testing.

RE: Minimum Design Metal Temperature Vs Minimum Design Temperature


Please specify which code you are working with since the terminology differs from one to another.
Assuming that you are using ASME B31.3, there are two definitions: the "Design Minimum Temperature" and the "Design Temperature". Following is an excerpt from the 2016 edition.

301.3 Design Temperature
The design temperature of each component in a piping system is the temperature at which, under the coincident pressure, the greatest thickness or highest component rating is required in accordance with para. 301.2. (To satisfy the requirements of para. 301.2, different components in the same piping system may have different design temperatures.)
In establishing design temperatures, consider at least the fluid temperatures, ambient temperatures, solar radiation, heating or cooling medium temperatures, and the applicable provisions of paras. 301.3.2, 301.3.3, and 301.3.4.

301.3.1 Design Minimum Temperature. The design minimum temperature is the lowest component temperature expected in service. This temperature may establish special design requirements and material qualification requirements.

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