API 650 Reinforcement / 5.7.2.3 and 5.7.2.4

[AOSSpecialties]

Good afternoon,

I am currently inspecting an existing storage tank ---- nozzles, reinforcement [or lack of]. I am trying to determine whether the client can receive credit for reinforcement, based on their nozzle neck thickness / distance from the shell. The client has ZERO previous history, information and/or any kind of drawings.

Can I get another opinion on the following 650 code literature to better understand how i can address and assess there not being a repad on nozzle greater than 3".


e) The material in the nozzle neck. The strength of the material in the nozzle neck used for reinforcement should
preferably be the same as the strength of the tank shell, but lower strength material is permissible as
reinforcement as long as the neck material has minimum specified yield and tensile strengths not less than 70 %
and 80 %, respectively, of the shell-plate minimum specified yield and tensile strengths. When the material
strength is greater than or equal to the 70 % and 80 % minimum values, the area in the neck available for
reinforcement shall be reduced by the ratio of the allowable stress in the neck, using the governing stress factors,
to the allowable stress in the attached shell plate. No credit may be taken for the additional strength of any
reinforcing material that has a higher allowable stress than that of the shell plate. Neck material that has a yield or
tensile strength less than the 70 % or 80 % minimum values may be used, provided that no neck area is
considered as effective reinforcement.
5.7.2.4 The following portions of the neck of a fitting may be considered part of the area of reinforcement, except
where prohibited by 5.7.2.3, Item e:
a) The portion extending outward from the outside surface of the tank shell plate to a distance equal to four times the
neck-wall thickness or, if the neck-wall thickness is reduced within this distance, to the point of transition.

Thank you!

 

[Geoff13]

What is your question? You have only copied the words in API 650.

In my experience most nozzles larger than 3" without a reinforcing pad are because the shell is thicker than required, and thus able to provide the required reinforcing area. The permitted neck area is usually quite small.

 

[JStephen]

See 5.7.1.8. Section 5.7.2 says nozzles "shall be reinforced" but that does not imply that a reinforcing plate is always required, as that reinforcing can be made by multiple means. See also J.3.6.1 that makes this very clear for smaller tanks. I believe this has all been made more clear in newer versions of API-650 relative to the older.
I would say in the case of an existing tank, the question that needs to be asked is, "Do you want us to confirm the design of the existing tank?" The presence or absence or size or thickness or weld details of fittings and reinforcement is a design issue, and can all vary considerably and still meet the standard.

 

[r6155]

@ AOSSpecialties
1)You must do the drawings and calculations.
2)Then you can do the inspections.

Regards

 

[AOSSpecialties]

Tank 1st shell course is 1" thick all the way around. There is no thickened insert plate around any of the 3" and 4" nozzles. As you can see in the photo I have attached, the 3" nozzle does have a small reinforcement pad installed, but does not meet code spacing and/or reinforcement size).

I know I can grandfather the inadequate weld spacing [toe of weld between two nozzles] by performing MT.

My question is, can I grandfather in the lack of reinforcement pad? I am pretty sure I know my answer, but would like a second opinion before I bring it to the table.

Again, inadequate reinforcement pad, no thickened shell insert, and nozzle distance does not meet code (neck thickness x 4).

 

[JStephen]

So did you actually do calculations to determine how much reinforcing is required and how much is furnished?

 

[HTURKAK]

Still i did not get the question.. If you are pretty sure for the answer , you should performed calculations to determine how much reinforcing is furnished..

I would like to remind that the reinforcing could be provided

i= with reinforcing pad
ii= extra material provided at the shell
iii= the nozzle neck

In your case , check the extra material provided at the shell ( beyond the thik. required ) and calculate the nozzle neck contribution. The nozzle neck contrbution is limited with upper limit (neck thickness x 4)

Or, provide more detail (thick. req . tr of shell , material of construction for shell and nozzles, nozzle dims, neck thk..) to get better responds..

 

[Geoff13]

If you don't have drawings, why do you think API 650 is the original design code? Is there at least a nameplate?

Without a code and year built how do you know this detail isn't in conformance with the rules it was built to meet? I believe the API 650 nozzle spacing rules were added in 6th Edition, so older tanks didn't have any code rules about how close together nozzles could be.

Without drawings to tell you what materials were used for the shell and nozzle neck it will be impossible to do accurate calculations of the required and available reinforcing areas. The API 653 rules for "unknown" materials assume conservative (low) values for yield and tensile, which may lead you to an incorrect conclusion about the reinforcing areas.

 

[IFRs]

The basics of reinforcement is to replace the material removed. So:
Assume all weld details are per API 650 or the code that the tank was built to
Assume the hole in the tank shell is 3 1/2" + 3/4" (API Max) = 4.25"
Assume the tank is 1" thick
Assume no excess shell plate thickness (see note 1)
The area removed is 4.25 square inches.
Assume the nozzle neck is Sch 80 (Extra Strong) seamless pipe with zero corrosion allowance and equal in strength to the tank shell.
The neck is therefore 0.300 inches thick
Assume the nozzle extends inside the tank at least 1.2 inches
The neck contribution is for a distance 4 x 0.300 inside and outside and within the tank shell.
The neck contribution is 4 x 0.300 x 0.300 x 2 x 2 + 1 x 0.300 x 2 = 2.04 square inches.
The repad must contribute the rest: 4.25 - 2.04 = 2.21 square inches.
Assume the repad is of equal strength as the tank shell.
Assume the repad has an inside diameter of 3 5/8" per API
Measure the repad thickness.
Measure the repad outside diameter before the weld
Calculate how much reinforcement the repad contributes above and below the hole.
Compare this to 2.21 square inches.
If all the assumptions are true and there is enough reinforcing area you are good.

Larger nozzles are unlikely to pass unless they are high off the tank bottom, made of thicker pipe than Sch 80 or the tank was overdesigned and there is a lot of excss shell plate thickness. Or there is an inside repad, etc...

Note 1: the area replaced only has to be equal the area required. If you have enough information you can calculate the required shell thickness and if that is less than the actual shell thickness you may use that in your calculations.