API 650 Roof Nozzle Design

[Holden1234]

Hello, I am a working on a project to add a 4” 300# nozzle to the fixed roof of a small (Diameter: 7’-3” Height: 12’)API 650 tank Annex J. This tank is already in service and is being pulled out to have its API 653 inspection. The nozzle will be installed during its outage. I have been reading through API 653/650 but I am having trouble determining what design calculations are needed to ensure that installing the nozzle acceptable. From what I have seen in the flanged roof tank sections, it seems the nozzle pipe thickness and dimensions are given. Dimensions are given for the welds, which show the combined thickness of the repad and roof should be a minimum of 1/2” thick. If this tanks’a roof is 1/2” is this all that must be checked for the nozzle to be installed as long as the nozzle schedule is standard size?Repads are not required but I am planning on having the thickness of the roof checked.I have attached a drawing of the tank and sections of API 650. Thank you in advance for your help.
Tank Drawing:

Standards text:

 

[Dhurjati Sen]

Have you made a site visit yet?

DHURJATI SEN
Kolkata, India

 

[JStephen]

From a practical standpoint, stresses in a small tank like that are pretty low, and it won't matter too much how you work it.
From a code-compliance standpoint, check if the tank falls under Annex F for pressurized tanks. If so, for some cases, it is specified that roof nozzles are to conform to shell nozzle requirements. This is a relatively recent editions, and if it is applicable, also check if your nozzle needs to meet the current code or the code of construction- I expect the current.
I'm not seeing your 1/2" requirement.
Also, it's not clear if you're saying the roof is 1/2" or asking, in the event it is- but on a tank that size, the roof would not normally be 1/2". That would tend to indicate major corrosion allowance on an acid tank or something like that. And if that's the case, you may want to beef up the nozzle pipe.
As you're discovering, there aren't normally any actual calculations required for a nozzle like this.

 

[IFRs]

API 650 does not require a 1/2" combined roof plate and reinforcing plate thickness, only that the repad be 1/4".
If you can post the tank drawing in a more readable format (pdf attachment perhaps) we can help a bit more.
I doubt if the roof plate is 1/2" thick...

 

[HTURKAK]

The drawing attached is not readable.. there is a roof vent at the elevation dwg of the tank and implies atmospheric... What is the content of the tank and what is the reason for outage and API 653 inspection ?

Pls provide more info to get more helpful responds..

 

[Holden1234]

I made two typos earlier. The roof is 1/4” thick. The requirement from API 650 that I am curious about is an arrow pointing to what looks like the combined thickness for the repad plate and the roofs thickness and has a specified thickness of 1/4”.

Since this is an annex J tank, repads for the roof flanged nozzles are not required, but I am curious what this dimension means and requires. If the roof was thinner than 1/4” would a repad be required to meet the dimensional requirement in the drawing?

This tank is taken out of service for its API 653 inspection and to make modifications on a set schedule of years and it is simply due for that inspection.

As addressed above by previous comments, it looks like there are no design calculations required for installing a flanged roof nozzle on an
Annex J tank. The nozzle just needs to meet the dimensions specified in Figure 5.19 and Table 5.14a.

 

[IFRs]

those arrows are meant to be for the repad only, the drawings are sometimes not the best..

 

[IFRs]

 

[Holden1234]

Thank you!