Background:

B31.3-2004, Table D300, Note 13: SIFs for branch connections are based on tests with at least two diameters of straight run pipe on each side of the branch centerline. More closely loaded branches may require special consideration.

B31.1-2001, Table D-1: No note similar to above. (I couldn't access 2004 edition, perhaps it has been added.)

B&PV Code-2004, Fig. ND-3673.2(b)-1, Note 10.(c): Similar note to B31.3 but in terms of arc distances in longitudinal and circumferential direction.

Application:

Multiple pressure reducing stations installed between 1980 and 2002 to B31.1, each with multiple valve legs, carbon steel piping, superheated steam below 700 Deg. F., 400 psig.

All stations typically have full size and reducing tees with other tees, reducers, elbows, WN flanges, and valves directly welded to them, and are to be evaluated under the current B31.3 code.

Questions:

1. Would it be accurate to say to the owner that welding other than two pipe diameters of straight pipe to a tee in steam piping would not have been acceptable under the B31 code unless a shell/brick type finite analysis was performed of the tee and adjacent component?

2. Did earlier codes assume that designers understood the two pipe diameter minimum spacing from other published works? What publications? Was the spacing just not understood to be a potential problem until Rodenbaugh's work in 1987?

3. As Rodenbaugh states in WRC 329, "We would rate the relative complexity of i-factors for pipe, elbows, and branch connections by the ratios 1:5:500." So, at this point in time, are there no other means (by WRC, Section III, or others) to evaluate such tee on fitting or tee on flange/valve fabrications other than shell/brick type finite element analysis?

4. Does the more recent understanding of the limitation of SIFs values for branch connections mean that it is advisable that owners assess older piping systems with congested piping arrangements because stresses in branch connections may be higher than once thought?

5. Or can owners relax since steam systems are typically subject to low cycle fatigue, and will the 20% or so relief for under 3125 cycles and other conservative judgments mean very few systems will begin to leak due to fatigue cracks?

Have I missed the "Recall" notice from the authority having jurisdiction or missed something else altogether?