BenStewart
Mechanical
- Jan 21, 2015
- 42
As part of a life extension study I'm completing a creep assessment in accordance with Part 10 of API 579 and following the Omega using isochronous curve method. The material is 5Cr-0.5Mo.
I have a few questions on two points if anybody is able to help. Thanks.
1. Triaxiality Parameter
I was reading PVP2017-65211 and noted the author advised when using this method that the triaxiality parameter, α[sub]Ω[/sub], would be set to 0 rather than 1. Out of curiosity I included this in my assessment and noted a significant enough change ~ +15% in time to rupture compared to using a triaxiality parameter of 1.
Is anybody aware of the rationale/justification of changing this parameter from 1 to 0?
2. Minimum vs. Average Data
As expected there is a large difference between the time to rupture when using minimum and average data, but what are the typical approaches you would use? I am inclined to do both and complete a risk assessment as it is an in-service piece of equipment, including appropriate inspection at the next turnaround.
Does anybody have access to the MPC Omega test data to view the scatter? Have you completed creep testing which has corroborate the use of minimum/average properties in an assessment? If so, what do the tests typically show, more in line with minimum or average?
I have a few questions on two points if anybody is able to help. Thanks.
1. Triaxiality Parameter
I was reading PVP2017-65211 and noted the author advised when using this method that the triaxiality parameter, α[sub]Ω[/sub], would be set to 0 rather than 1. Out of curiosity I included this in my assessment and noted a significant enough change ~ +15% in time to rupture compared to using a triaxiality parameter of 1.
Is anybody aware of the rationale/justification of changing this parameter from 1 to 0?
2. Minimum vs. Average Data
As expected there is a large difference between the time to rupture when using minimum and average data, but what are the typical approaches you would use? I am inclined to do both and complete a risk assessment as it is an in-service piece of equipment, including appropriate inspection at the next turnaround.
Does anybody have access to the MPC Omega test data to view the scatter? Have you completed creep testing which has corroborate the use of minimum/average properties in an assessment? If so, what do the tests typically show, more in line with minimum or average?
