teokal
Mechanical
- May 4, 2007
- 76
Hi everybody,
We are fabricating a Column with dimensions 3700mm ID, 17mm thickness, SA516 Gr70 material (TL-TL does not matter). The Column is now at its final stages of fabrication, and it has a lot of nozzles welded to its shell. These nozzles do not give us a lot of position choices, and so we have used only one pair of positioner for each section (Column is fabricated in 2 sections, and is scheduled to be joined in one with a closure weld). Now that the Column is everyday heavier (by installing internals), it has created some dents at the positioners area. The dents are approximately 350mm by 1000mm, with maximum depth (localized) 14mm.
To my mind, this is a dent, and its (project specific) tolerances are 3mm per 3m of length. ASME VIII Div.1 does not address any tolerances for dents. But it does provide tolerances for Out-of-roundness (UG-80).
The question is: what is the difference between a Dent and an Out-of-roundness? Could we use the out-of-roundness tolerances for this surface issue (allows 1% of ID, in our case 37mm - due to external pressure, for a length of 4.2m between stiffening rings, the allowable depth is 13,6mm which is very close to the 14mm maximum depth measured)? Should out-of-roundness be measured on full length of a shell section/course? if not, what would be the difference from a dent?
Thank you in advance, everybody!
Only best result in absolutely necessary time
We are fabricating a Column with dimensions 3700mm ID, 17mm thickness, SA516 Gr70 material (TL-TL does not matter). The Column is now at its final stages of fabrication, and it has a lot of nozzles welded to its shell. These nozzles do not give us a lot of position choices, and so we have used only one pair of positioner for each section (Column is fabricated in 2 sections, and is scheduled to be joined in one with a closure weld). Now that the Column is everyday heavier (by installing internals), it has created some dents at the positioners area. The dents are approximately 350mm by 1000mm, with maximum depth (localized) 14mm.
To my mind, this is a dent, and its (project specific) tolerances are 3mm per 3m of length. ASME VIII Div.1 does not address any tolerances for dents. But it does provide tolerances for Out-of-roundness (UG-80).
The question is: what is the difference between a Dent and an Out-of-roundness? Could we use the out-of-roundness tolerances for this surface issue (allows 1% of ID, in our case 37mm - due to external pressure, for a length of 4.2m between stiffening rings, the allowable depth is 13,6mm which is very close to the 14mm maximum depth measured)? Should out-of-roundness be measured on full length of a shell section/course? if not, what would be the difference from a dent?
Thank you in advance, everybody!
Only best result in absolutely necessary time
