Design temperature

Please, reformulate your question. It is not possible to understand what is your problem the way you posted.

Crajkumar,

It looks like you might have mixed up the basis for your question.

Should it have been:

"If the upset temp (ex: 120 Deg F) is less than the steam out temp (ex: 400 deg F), what is the design temperature?"

I recommend that you:

a) Determine the applicable design Code (i.e.: ASME B31.1, B31.3, etc.)

b) Apply the criteria from the Code