SIF For Stub on/ Stub in connection

Dear All

We are in the process of flexibilty analysis of 4" size piping. A branch connection, stub in / stub on, of the same size is taken from the main line. The appendix D of ASME B31.3 does not cover the inplane and outplane SIF for this type of connection.

Can any one acvice how can one calculate the inplane and out plane SIF for the above said connection.

BR

Ikram

Ikram,

In your instance B31.3 does, in fact, address branch SIF’s in the form of reinforced and unreinforced fabricated tees. As you indicate that the branch and header are of the same size, the respective in-plane and out of-plane factors for a d/D ratio of 1 would apply.

It is only where your d/D ratio starts being less than 1, examples being for bleed-off’s, drains, small branches, etc. that B31.3 does not handle this extensively. In fact, note 12 in appendix D states that equivalent SIF’s adopted for these type of branches are “nonconservative” i.e. the stress concentration is a lot higher than you would think.

In such instances my advice would be to address this in one of two ways.

a) Nozzle and branch loading of this ilk is tackled quite extensively by the seminal, Welding Research Council article No. 297 – which facilitates calculating stresses from first principles, and may be studied and applied by a competent piping engineer.
b) Paulin Research Group has developed an excellent suite of analysis software to handle such nozzle and branch loadings, and may be purchased to aid your pursuit.

The bottom line is that there is no “quick fix” which we all, as human beings, initially may hope for. Even by wading through WRC 297 you’ll appreciate the complexity of the problem which you highlight and that commensurate time should be allocated to appreciate and understand how sophisticated the underlying solution is.

2M

2M

You have discussed very useful information. In my case, can i use the unreinforced tee as stub on connection in flexibility analysis software as per your below discussion and conclude the matter.

Regards

Dear 2M

I was waiting for your response. However, the matter is conculded as; the pipe to pipe connection is assumed to be un-reinforced tee and the SIF inplane and outplane is taken from appendix D of ASME B31.3.

The same values were incoperated in the stress analysis program and needed reinforcement. A pad of 5mm were installed to satisfy ASME B31.3 requirement. Now to implement the same modifiaction in the field, the pad width is required also.

So 2M, can you plaese advice for how much width for the pad(5mm thk) be selected for a pipe of 4" size and what the standard practice prevails.

Can you plaese provide your email address, if convenient.

Waiting for you prompt response.

Best regards

Ikram

I like it very much thanks for sharing this information with us….