What is the design temperature according to ASME-I?

[Bhupinder1]

Looking at para-27.4.2, in the first line it says the temperature is the mean wall temperature and then in the end of the second line it says it should be higher than the saturation temperature of the fluid (tubes that do not absorb heat).

For example: Case - tube that absorbs heat.
The mean metal temperature is 340 degC.
The saturation temperature is 374 degC.

what would the design temperature - is it 340 or 374 degC? Thanks.

 

[weldstan]

The word "should" is a recommendation not a requirement. But it is a sound recommendation.

 

[metengr]

Yes, it should be 374 deg C in your application. The paragraph was intended to ensure the calculated mean wall temperature is equal to or greater than saturation temperature, and not below it.

 

[Bhupinder1]

Metengr - in that paragraph in the first line it says the mean metal wall temperature and then in the second line which is related to tubes that do not absorb heat to use at least the saturation temperature. In my case the tube is absorbing heat, does that means I can use the mean metal temperature which would be 340 degC? Thanks.

 

[metengr]

Bhupinder1
PG-27.4.2 The temperature of the metal to be used
in selecting the S value for tubes shall not be less than the
maximum expected mean wall temperature, i.e., the sum
of the outside and inside tube surface temperatures divided
by 2. For tubes that do not absorb heat, the metal
temperature may be taken as the temperature of the fluid
within the tube but not less than the saturation
temperature.

Per the above, if tubes absorb heat, you shall use the mean wall temperature per above at 340 deg C.
For tubes that do not aborb heat it is recommended to use the saturation temp as the mean wall.

In looking over your case, I would select the saturation temperature as the mean value being more conservative. You are not required but I like the added conservatism, which is why it is only a recommendation.

 

[Bhupinder1]

Thanks metengr,

To understand this correctly 'shall' means I'll have to use it as the design temperature and in the second line it's only recommended, hence it's not necessary to use it.

In old ASME - I, the minimum design temperature was 700 degF (371.2 degC) - in which edition did it changed (ie 700 degF was removed)?