KevinNZ
Mechanical
- Jun 12, 2003
- 850
B31.1 102.2.4 allows for occasional short operating periods at higher than design pressure or temperature.
In this case we can have higher hoop stream up to 20% over maximum allowable stress for the coincident temperature.
But what if you are only increasing thermal operating range (Displacement Stress) and not increasing the pressure. For example the design range is 10C to 200C (180C range) and the system is operated from -5 to 200C (205C range, ~11% increased in displacement stress.) There is no increase in the hoop stress or decrease in the allowable hoop stress.
Does this clause only apply to hoop stress and Displacement Stress must still be under allowable? As written it only requires the hoop stress check.
What about sustained longitudinal stress? This must go up with pressure increase. But you cover this with occasional load allowance in 102.3.3.
In this case we can have higher hoop stream up to 20% over maximum allowable stress for the coincident temperature.
But what if you are only increasing thermal operating range (Displacement Stress) and not increasing the pressure. For example the design range is 10C to 200C (180C range) and the system is operated from -5 to 200C (205C range, ~11% increased in displacement stress.) There is no increase in the hoop stress or decrease in the allowable hoop stress.
Does this clause only apply to hoop stress and Displacement Stress must still be under allowable? As written it only requires the hoop stress check.
What about sustained longitudinal stress? This must go up with pressure increase. But you cover this with occasional load allowance in 102.3.3.
