Stiffness and Allowable Loads for API 650 Flush-Type Shell Connection

[DanielChow]

Hi all

My refinery is constructing two new API 650 storage tanks of 44m and 47.5m diameters. Both of them have at least one flush-type shell connection per section 5.7.8 of API 650.

We are trying to determine the stiffness coefficients and allowable loads for these nozzles. Annex P within API 650 outlines the method for checking nozzles conforming to Table 5.6a and Table 5.6b, i.e. having L/2a (as shown in Figures 5.2) of at least 1.0., but flush-type shell connection doesn't meet the minimum elevation requirement per Table 5.6a/b. We therefore concluded that Annex P is probably not the appropriate reference for finding out the stiffness coefficients and allowable loads for the flush-type shell connections.

Any idea where/how the stiffness coefficients and allowable loads for flush-type shell connections can be determined.

Thank you in advance for any reply/input.

Regards
DC

 

[JStephen]

I think you'd be looking at a finite element analysis.
Depending on the circumstances, it might be cheaper to rearrange the piping or add flexibility into the lines than to analyze the nozzles.

 

[DanielChow]

Hi JStephen

Thanks for your thought. The piping has some properly placed bends/elbows, based on experience, looks flexible.

The piping designer designated the flush-type shell connection as an ANC in Caesar. The analysis yielded a set of forces and moments at the ANC; and indicated the piping as meeting B31.3 code stress requirement.

I just wonder how the aforementioned set of piping reaction forces and moments at the ANC node could be qualified as acceptable for the flush-type shell connection. Would be most appreciative on any further thought on this.

Many thanks.

DC

 

[Duwe6]

API-650 is Rules-based. Thus rigorous nozzle calc's are outside its scope. If the pipe meets B31.3 and sends its thermal growth away from the tank [hence the 'pipe anchors' portion in API-653 inspx] and the flanges can be aligned by hand; no chain-falls or hydraulic jacking needed. then the nozz stress meets the 650 rules.

I would only do FEA or other calc's if a pipe anchor or restraint was needed close to the tank. The 650 rules [actually] work.

 

[DanielChow]

Hi Duwe6

Thanks for contributing. May I know where is "'pipe anchors' portion in API-653 inspx" stated? Just can't locate it in the latest API 653 I'm having (4th edtion, addendum 3, Nov. 2013).

 

[Duwe6]

Pipe anchors are an inspection point listed in the External Inspx Checklist, Appendix C.