Pressure Rating of Extruded Headers 1

[Hutamaki]

Hi, i am trying to find the pressure rating of a 6 inch SCH 40 ASTM A234 WPB equal tee according to ASME B31.8 (similar to ASME B31.3). The code requires a dimension Ro (radius of curvature) which the supplier does not have and is not sure about. I check some old material certs and it does not give this dimension. ASME B 16.9 does not specify this dimension either. I do not fully grasp what B16.9 is saying under 2.1. (must i use the calc for a straight 6" SCH 40 pipe with WPB SMYS to get the rating?).

Where do i find the Ro for the calculation, is this the right way of calculating the pressure rating or is there some easier way to do this??

 

[metengr]

The fitting that is purchased to and stamped as ASME B16.9 is specified by pipe NPS, Sch per this specification. The straight tee as specified for 6" Sch 40 piping will have been designed for this pipe size if supplied under B16.9 - this is what 2.1 is saying.

If your pressure and temperature conditions for straight pipe required 6" Sch 80 instead of Schedule 40, the fitting would be sized for 6" Schedule 80 under B16.9.

According to B16.9, the supplier of the fitting must have demonstrated by design analysis or proof testing that the NPS and Schedule of their fitting meets B16.9

 

[Hutamaki]

metengr, thanks for the quick response.

So if i have a 6" SCH 40 A106 Gr B Piping. Using B31.8 (with location class 1) seamless pipe at 20degC i calculate a pressure rating for the pipeline of 176 barg.

If i ordered a 6" SCH 40 A216 Gr WPB (same SMYS) then it would have the same rating i.e. 176 barg?

If it is this easy, why does the code give detail explaination and method for calculating the pressure rating using the radius of curvature? Does this calculation still have to be done as part of the design documentation?

If i did want to do the calculation, where would i find the radius of curvature Ro??

Further, does the same principle apply to all other fittings (reducers, end caps, tees etc...)?

 

[metengr]

This may help you - please read 302.2.1 and 302.2.2 of B31.3 (I don't have the other Piping Code handy). The Code also allows one to fabricate a branch connection using the design requirements for branch connections to assure adequate reinforcement.

 

[ytse]

I believe you are trying to apply the rules for "Extruded outlets" on wrought steel tee per B16.9. Those are different things according to the code.
In paragraph 831.42 and table 831.42, it is stated in both section(a) and (b) that "Smoothly contoured wrought steel tees of proven design are preferred." This means tees per B16.9.
In addition, paragraph 2.1 of B16.9 stated that "The allowable pressure ratings for fittings designed in accordance with this Standard may be calculated as for straight seamless pipe of equivalent material (as shown by comparison of composition and mechanical properties in the respective material specifications) in accordance with the rules established in the applicable sections of ASME B31, Code for Pressure Piping".
So if your 6" SCH 40 A106 Gr B Piping is good for the 176 barg per B31.8, then a sch 40 WPB fitting made to B16.9 standard is good for that same pressure under B31.8.