Assessing nozzle thicknesses to API653
Assessing nozzle thicknesses to API653
(OP)
I have been asked to look in to the assessment of BST nozzles to API653. The code basically says to evaluate the thickness with the 'as-built standard'. However, often these tanks were built to an unknown code.
I have therefore been evaluating to both API650 (essentially Sched 80 pipe) and API620 (basically Standard weight pipe), as they are both API codes. Previously my clients accepted that if the nozzles were below API620 thickness, then they were replaced with Sched 80 pipe. - No problem.
However recently I have struck a client wanting to evaluate the thickness rather than just use a figure from the codes.(ie they don't want to spend the $$ I think)
Can anyone point me in the right direction as to how to assess these nozzles? Is there a basic (even not-so basic) formula somewhere that I'm missing? Or am I OK to continue using the API620 thicknesses as minimums?
Also - What happens when you install a new nozzle with Sched 80 pipe, then take thickness readings and find that it's below the thickness in API650 Table 5-6 (even if it's only 0.2mm say?)
I have therefore been evaluating to both API650 (essentially Sched 80 pipe) and API620 (basically Standard weight pipe), as they are both API codes. Previously my clients accepted that if the nozzles were below API620 thickness, then they were replaced with Sched 80 pipe. - No problem.
However recently I have struck a client wanting to evaluate the thickness rather than just use a figure from the codes.(ie they don't want to spend the $$ I think)
Can anyone point me in the right direction as to how to assess these nozzles? Is there a basic (even not-so basic) formula somewhere that I'm missing? Or am I OK to continue using the API620 thicknesses as minimums?
Also - What happens when you install a new nozzle with Sched 80 pipe, then take thickness readings and find that it's below the thickness in API650 Table 5-6 (even if it's only 0.2mm say?)





RE: Assessing nozzle thicknesses to API653
I would be wary about recommending changes to a tank "built to an unknown code" based on API-653. Or to put it more correctly, the better recommendation might be to demolish the tank and build a new one to a known standard.
On the nozzle wall thickness, refer to ASTM A53 or similar pipe codes as applicable. Pipe wall thickness can vary up to 12.5% in some of the standards, and that would govern rather than the normal allowable shell underrun.
RE: Assessing nozzle thicknesses to API653
You say that the tanks are non-Code. Does that mean they do not comply with a recognized Code/Standard or does it mean that you have lost the nameplates or documentation on the tank?
Joe Tank
RE: Assessing nozzle thicknesses to API653
Thanks for the tips. Just as I thought - no easy answer.
As for the non-code tanks - I mean that there are no records of what the tank was built to. ie no nameplates, no paperwork etc, and they were generally built before I was born...
Cheers
Dave