You might indeed be correct. Is this barred tee fitting going to be used in a pipe line for gas transmission service (ASME B31.8)? If so, Appendix C lists both Standard Specifications A-694 and A-234. I would review each Standard Specification and make a side by side comparison. If you can provide more detail, it might help.

Firstly, i correct a mistake, the pipeline is API5L Gr.B. Thank Metengr for your so quickly response. This barred tee is used in curde oil transportation pipeline. If somewhere is not clear, please tell me, i am very glad to provide the detail information, because i have been thinking for a long time.  

I checked with ASME B31.3 Process Piping, and the piping listed for API 5L Grade B has an allowable stress of 20 Ksi up to 400 deg F, and SA-234 WPB is the same values.

The only help I could think of to bolster your argument for using SA-234 WPB versus A-694 is that the Table of materials in Appendix A of B31.3 lists SA-234 with published allowable stress values. ASTM A-694 is unlisted but could be used; however, you would need to establish the allowable stress values for this application.

Regarding the allowable stress of API5L Gr.B and SA-234 WPB, you are right, but i don't think to check them with ASME B31.3 but with ASME B31.4. In addition, SA-694 is listed in the Appendix A of ASME B31.4.

In the other hand, the allowable stress difference of SA-694 and API5L Gr.B is so lager that it maybe need to be heat treatment after welding to reduce stress. Since the allowable stress of SA-234 WPB is same as API5L Gr.B, in this case it is no need to do heat treatment. Is my point is correct or not?

The A-694 F65 material would need to be evaluated for PWHT based on API requirements. For some of these higher strength materials, the mechanical properties can be reduced by PWHT, which may or may not help your cause. Using SA-234 with the API 5L Grade B pipe material, you would need to follow API requirements regarding the need for PWHT, I don't have access to API Standards.