tr6
Mechanical
- Oct 2, 2002
- 81
We have a number of pressure vessels built to ASME Sec VIII in the '60s that are now being assessed for brittle fracture due to possible autorefrigeration conditions. No consideration for low temperature (less than -20 deg F) were taken in the original design, and therefore assume that the original hydrotest was performed at "ambient" temperature.
A Level 1 assessment has been performed and determined that the corresponding MAT exceeds (is warmer than) the autorefridgeration curve over the pressure range of 0.4 MAWP to the full MAWP with a maximum MAT of 89 deg F at the MAWP.
Performing a hydrotest under Section 3.4.3.2 at 1.5 x MAWP lowers the MAT to below the autorefrideration curve; however, a question regarding the hydrotest temperature has been raised. If the hydrotest temperature is determined by adding 30 deg F to the MAT, to prevent brittle fracture, then the hydrotest temperature should be 119 deg F. Kind of impractical for a 9' dia x 80' long vessel. However, as stated above, the vessel was probably hydrotested at "ambient" temperature at the time of original construction over 40 years ago with no apparent damage due to brittle fracture.
So, I guess the question is. "Is it reasonable to perform a hydrotest at a lower temperature than the MAT + 30 deg or even the MAT itself, given that it has already been performed, and not be concerned about brittle fracture occurring?". Obviously, "ambient" temperature would be preferred.
A Level 1 assessment has been performed and determined that the corresponding MAT exceeds (is warmer than) the autorefridgeration curve over the pressure range of 0.4 MAWP to the full MAWP with a maximum MAT of 89 deg F at the MAWP.
Performing a hydrotest under Section 3.4.3.2 at 1.5 x MAWP lowers the MAT to below the autorefrideration curve; however, a question regarding the hydrotest temperature has been raised. If the hydrotest temperature is determined by adding 30 deg F to the MAT, to prevent brittle fracture, then the hydrotest temperature should be 119 deg F. Kind of impractical for a 9' dia x 80' long vessel. However, as stated above, the vessel was probably hydrotested at "ambient" temperature at the time of original construction over 40 years ago with no apparent damage due to brittle fracture.
So, I guess the question is. "Is it reasonable to perform a hydrotest at a lower temperature than the MAT + 30 deg or even the MAT itself, given that it has already been performed, and not be concerned about brittle fracture occurring?". Obviously, "ambient" temperature would be preferred.
