Dear Experts,

I have a confusion concerning the type of carbon steel Tee to use in FEATools whether I should use light weight or medium weight Tee. I tried to check FEATools User Manual and found what seems to be contradicting definitions of light Tee in three different locations:

1- in page 32, it is mentioned that "Light tees have average body wall thicknesses of between 1.1 and 1 times the nominal thickness of the attached pipe."

2- in page 66, "In a small percentage of cases, the thickness of the stamped B16.9 welding tees measured throughout the body of the tee was found to be less than the nominal thickness of the attached straight pipe, .... Most of the very thin walled B16.9 tees measured, (called light tees above), are in ductile, alloy materials.

3- In Featools help, "Light - Thinner than nominal wall tees. If the welding tee thickness is known to be lighter than the nominal wall,this option should be selected. This option will yield the highest SIF and largest difference with ST LLC 07-02."

On the other hand, I received lately files from a client for Tee SIF calculations comparing light weight and medium weight Tees. the Tee OD for light weight seems to match the OD of the attached pipes, while medium weight Tees OD are a bit larger than the attached pipe OD. (I attached the files of FE Pipe)

So is the light weight Tee of the same thickness as the pipe? thinner? or thicker?

Thanks a lot in advance.

Tees of years ago had more than enough wall to maintain the pressure boundary. Forges now are able to produce acceptable pressure-strength fittings with much less wall. So here's the disconnect - acceptable pressure strength is not directly related to the mechanical strength of the component where mechanical strength will set the component's SIF & SSI (stress intensification factor and sustained stress index, respectively).
As I understand it, you can now purchase a pressure-qualified tee that will be thinner than the "matching" straight pipe for the required pressure service. In order to get a more-accurate structural response out of such components, FEATools can run calculations for light to heavy wall tees.
In general piping system design, you probably do not have firm data on the tees you will be using. The selection provided by FEATools allows you to run 'what if' scenarios or check the most conservative case (thinnest wall).
I believe statement 1- above is in error. I will report it to the FEATools people. Thank you.

Thank you Dave for your answer. However the confusion with the client is still the definition of medium weight Tees as compared to heavy weight Tees. He is considering the medium weight as 1.5X thicker than the pipe while I am debating that this is heavy weight. Is it that the definition of weight of tees has changed over the years (because he is using FEPipe version 1.1 which is very old).

Dear Dave,

I performed the same analysis of the files attached before (36x24 TEE) with both light weight and medium weight options on FEATools. Since I do not have FETee, I asked the representative of Intergraph and PRG products in UAE to use the .fetee files generated by FEATools as an input to FETee and generate the detailed reports of the Tee geometries. The representative sent me reports that show the following:
1- light option Tee thickness is the same as that of the pipe.
2- medium option Tee thickness is 1.5 times the thickness of the pipe.

This totally contradicts with FEATools information in the help file where it mentions that the light tee thickness is less than the pipe thickness and heavy weight thickness is 1.3 times the pipe thickness!! Can I seriously trust the results of FEATools now??

I agree that the FETee review of a tee entered as light/medium/heavy will show a heavier header wall thickness ratio (tee type wall/light tee wall) of 1/1.55/1.89.
But I also notice that the stiffnesses entered into CAESAR II by FEATools are increasing in a proper fashion. For example, the in-plane bending stiffness for the branch is 5.9/10.7/19 (*1e6 in-lbf/deg) for light/medium/heavy tees, respectively.
CAESAR II uses the stiffnesses from FEATools, not those FETee wall thicknesses. I will ask the people at PRG to comment.

I asked Tony about the light/medium/heavy settings in FEATools. He says: "Realistically, we don’t see contoured tees significantly less than the nominal wall, although the argument has been made that they can get as small as 87.5% of the nominal wall as long as there’s a calculation that shows that’s ok, or there’s a burst test." At the other extreme, the older B16.9 tees were heavier.
So now, when I think of tees as light/medium/heavy in FEATools terms, the light is matching pipe wall and it gets heavier from there.

Thank you Dave for your response. Can you please ask PRG to update the help file and user manual to transparently reflect the actual thicknesses FEATools uses for each tee type? the way the information is presented now is totally misleading.

Thanks.

I have passed your request for change to PRG.

Thank you Dave.