Wrapper plates vs collar plates for mild steel tees 2

[win]

I have a question on mscl water pipe design. For a 30' equal mild steel tee, according to awwa m11 on reinforcing plate design we have to use wrapper plates as the ratio of branch/main diamter is 1.0 (more than 0.7). However looking at the shop drawings given by a few pipe manufacturers they only use collar plates. Any opinions on this? Is it a norm for tees with such ratios to just use collar plate reinforcements?

 

[rconner]

Was first curious do you really mean 30' (or instead 30-inch)?

 

[win]

Sorry, I meant 30 inch.

 

[rconner]

Just an opinion, as of course little project information is supplied in this inquiry, e.g. details of the design as well as actual service/application requirements. What do the project specifications require for these fabrications (while I think it has been around in various forms for more than a half century, AWWA Manual M11 is of course not really a code or specification, but instead a "Guide")? In this regard also, I note that e.g. Table 13-2 of this manual (I see referring to e.g. the ratio of d/D>.7 pointing to "collar") is also headed "RECOMMENDED reinforcement type..."(I supplied the caps), and it thus might be argued recommended does not mean required.
Nevertheless, I know M11 however does in areas refer to codes in areas e.g. , "Wrappers and collars are designed similar to the method described in Section VIII of the ASME Boiler and Pressure Vessel Code. This code provides that the cross-sectional area removed at the branch is replaced in the form of a wrapper or collar..." If it turns out that the project specifications are not clear as to what is required to be furnished for these items, perhaps the vendor and designer of the reinforcement could thus be now approached and asked for any available details of their design, e.g. per the removed area/replacement approach, or other stress calculations and/or proof-of-design testing etc, as it would seem all reputable parties would want them to actually work on your project.

 

[rconner]

Oops, I meant (and as you indicated) d/D>0.7 pointing to "wrapper" (meaning some reinforcement all around pipe).

 

[robyengIT]

I am using AWWA M11 irregularly for design of Tee branch for prestressed concrete pipe (water distribution)in Europe. I understand that M1 is only a guide, but since here we don't have even that, we consider M11 as ruling Standard : therefore I assume table 13-2 as ruling in conformity with the PDV calculation.
For Your convenience I attach the ref part of "AWWA M11 4th edit. (2004) amended with errata (2005)"

 

[win]

Interesting points indeed. After several discussions with my superiors we decided that collar, wrappers and crotch plates will not be needed for our case. Referring to the earlier paragraphs before table 13-2 which also can be seen in the above attached, it was mentioned that

"For ordinary waterworks installation, the wall thickness commonly used is much greater than pressure conditions require. Consequently the lowered safety factor of fittings having the same wall thickness as the straight pipe still leaves adequate strength in most cases, and reinforcing may be unnecessary"

In addition we also noticed that the PDV formula does not contain the element of pipe thickness. As such, say a 750mm pipe/branch with super thick plates will still have the same PDV as a 750mm pipe/branch with very thin plates however with the former being 'over designed' is unlikely to need any reinforcement' Due to this, we concluded that the operating and design pressure for the fittings must be compared first before deciding on the need for reinforcing collar/wrappers.

This is our current understanding in this matter. Any comments is much appreciated!