Proof Test Factor of Safety

[rumandcola]

Under ASME section VIII division 1 the calculations use factor of safety that is based on the minimum of tensile strength/3.5 or yield strength * 2/3. When performing a proof test according to UG-101 the burst pressure is divided by 4. My question is why the difference in safety factors? Is this something left over from the pre '99 code addenda or are they trying to maintain an additional factor of safety on parts of greater complexity.

 

[John7474]

This is solely my opinion.
80/4 ~20…….
70/3.5 ~20

Let’s say the listed minimum TS of the CS that makes the vessel is 70 ksi. While performing the burst test, the vessel is not going to rupture at 70 ksi, rather it will withstand stress higher than this value, as 70 ksi is the minimum TS of the tested specimen.

The design pressure formula is based off of the minimum tensile stress.