Hi

I am working in stress analysis, my question is the next:

How should I consider the SIF for wye 36 inches?

Regards

Alejandro Jofré

Mechanical Engineer

JRI

In my limited experience in Combined Cycle power plants(mostly Hot Reheat Systems) a SIF of 2.0 was used as a Conservative approach.

I beleive FEpipe or similar software could be used for the evaluation of SIF for these items not defined in the Codes

A SIF of 2.0 based on no data!!! Wow thats amazing!!!! You don't know what the D/T ratios are or what the angle of the Wye is or anything else.

Seeing as how we are picking numbers from thin air why don't you calculate the SIF for a pipe to pipe intersection and double it... That seems "Conservative" to me.

The highest qualty answer which is the best solution is to derive an SIF via skilled competent use of an FEA program. FEPIPE is recognized as one such program used widely for this type of issue.

Now let me go consult my OUIJA board to see if the system I am looking at complies with the code stresses or not.

The bottom line here is that (except for the French code CODETI and the new EN-13480) no piping Codes address a "wye" fitting. Therefore, since there are no Code guidelines you are left to make your own engineering judgement call.

Two options are:
1) Utilize FEA software as mentioned above
2) Contact the fitting vendor and ask them for the SIF (maybe they can provide this information).

What do CODETI and EN-13480 say about a "wye" fitting (actually a spherical wye)?

i = 0.9 / h^.667
where h = 2*en/dm
en = wall thickness of the sphere
dm = diameter of the sphere

Before you use this information, please look it up and verify it yourself.

I recently did a 48X42 Wye on a charge gas compressor line. I got SIF's using FEpipe. There is template in FEPipe for a WYE fitting

Ravi Seshadri
Sarnia

There are some limitations(thickness, D/t ratio) to use the template of Wye in FE/Pipe. This template may not be applicable to the case with thin walled(ex: 36” pipe, STD WT.) Wye or an integrally forged product. ASME B31.3 asks to meet the requirements the para.304.7.2 for unlisted components.
To get the valid SIF by using FEA, as John mentioned, only qualified FEA user should get accurate values. For some cases, thin walled Wye or Laterla with sharp angles, only by entering the SIF into Caesar II may not be enough to verify these components.

In my opinion; if your pipe is major system with high pressure, you’d better let vendor design it and you provide your design conditions including loads. Some vendors such as WFI and GCC provide the SIF with FEA and busting test. This case will result in not only the higher engineering and material cost but also delay of engineering schedule.
If you piping is not a critical system, use very conservative values…..