API 650 Appendix A nozzles

[Addison2481]

Our company produces field erected waste water treatment plants (large circular open top tanks on concrete slabs). The bottom shell course welds to a base ring channel that is embedded into the concrete. Occasionally, we get jobs that have specs that reference API-650. In those cases, we do the shell calcs based on API-650 even though our tank arrangement doesn't meet the exact definition of an API tank (no steel bottom or annulus ring). The customer is normally not looking for a strict interpretation of the API code in most cases.

We just booked a job that includes API-650 Appendix A in their specs. I have asked our application engineering group to verify if we must follow the complete provisions of API since this job requires the calcs and drawings to bear a FL PE stamp. That finally brings up my question. With respect to the nozzles and re-pads. We did an exact copy of this job for this same customer in 2008. The nozzles on that job did not include re-pads. Based on what I see from my initial review, there will not be enough integral reinforcement to exclude the need for re-pads if the customer dictates that we strictly follow API this time around. I see there are a couple of exceptions listed in A.7 related to nozzles. I assume the requirements set forth in 5.7 & 5.7.2 are still in play for Appendix A tanks. Section A.7.2 sites 5.7.6, so this made me question exactly what was inclusive. I understand that item in Appendix A are only exceptions and the remainder of the code is still in play. I’m just not sure how it all ties together when Appendix A is used.

Sorry for such a long post. Just wanted some expert feedback from the API community.

 

[JStephen]

I don't have the standard in front of me to look up the sections. But one thing you might consider is using the basic code instead of Appendix A. In Florida, this should still let you use A36 or equivalent plate, but the required thickness will be less, so you would have less reinforcing required and more excess plate thickness to use as reinforcing.

 

[IFRs]

There is no A.5.7 or A.5.7.2 in the latest edition. There are sections A.7 and A.7.2 which relate to nozzles. These sections essentially say to design nozzles and manways in accordance with the basic standard except for weld spacing and NDE. If you have done the calculations and repads are required then put them on. If the last tank was not done with repads (and everything is truly identical) then quickly buy more insurance. Note that API 650 allows you to take credit for things like portions of the nozzle neck to reduce the thickness of the repad, sometimes eliminate them altogether. Good luck and keep us posted!

 

[Addison2481]

Thanks for the quick replies...

JStephen,
I also considered this approach since we normally use the basic code. I would have to see of the customer will allow this exception.

IFRs,
What Addendum is most current, I have API 650, 11th Edition, Addendum 2. I checked with IHS a few months back and was told that this was the most recent version?

 

[IFRs]

You have the most current version.