ASME Sec.8- fig. UCS-66.2

You should be able to calculate an adjusted MDMT per the steps in UCS-66. Then, for minimum hydro test temperature, increase this MDMT by 30F (17C) per UG-99(h).

Thanks codeeng! But what is not clear how did they arrive at this value of 30F(17C). Of course it is given in UG-99(h). But what is the calculation basis for this. Thanks.

Here is a thread that contains a file attachment regarding ASME Section VIII impact testing;
thread292-116022

The 30F is just margin because your stress at hydro testing can be higher than operating.

Codeeng, you are right that 30F is the margin to take care of the higher stress at hydrotest. I am only curious to know the basis for this value 30F. My question is why 30F, why cant 20F or 40F. I am sure the Code must have had some basis in arriving at this margin 30F. I only want to know what is this basis. Thanks

Your original question was:

"....the basis for arriving at 17 deg from Fig-UCS-66.1 is not clear."

The 17C (30F) does not come from UCS-66.1. Its a margin to be added to the MAWP calculated from UCS-66.1.

As to why 30F ? Its a safety factor established from experience. It is not calculated, its just a rule. There are many other Code requirements based on rules rather than analysis.