Thermal Stress Relief AWWA D100

[emart0429]

I'm hoping someone can help me out with some confusion I'm causing myself in regards to thermal stress relief for AWWA D100 water tanks. I'm working on a Section 14 tank with the bottom shell course over 1" thick (1.25" thick). I'm trying to figure out if the thermal stress relief requirements indicated in Section 14.3.2.6 (D100-21) would require the reinforcing plate around the manhole to be installed along with the 36" diameter manhole neck plate prior to thermal stress relief. Or, does the thermal stress relief only have to be done for the actual 1.25" plate and the neck? Then out in the field the 1.25" reinforcing plate is installed and welded w/out thermal stress relief.

Seemed simple enough to me initially to require the reinforcing plate be welded to the shell prior to thermal stress relief. But, the reinforcing plate for the manhole is tombstone shaped and extends all the way to the bottom plate of the tank. In this case, would a part of the bottom plate (some length of and annular ring) then be required to be welded to the assembly prior to thermal stress relief? That doesn't make sense, which made me lean toward not requiring the reinforcing plate to be welded into the assembly prior to thermal stress relief.

Any input would be greatly appreciated. Sincerely,
Erik

 

[JStephen]

See the parallel requirement with some clarification in API-650, Sections 5.7.4.2-5.7.4.4.
Where specifics are not stated in AWWA D100, I would assume the API-650 requirements were generally intended or acceptable.
Then see Detail B in Figure 5.8 of API-650, which shows a tombstone-repad being shop-welded to the shell plate on the bottom side, without the fillet in between being connected to the bottom.

 

[emart0429]

See the parallel requirement with some clarification in API-650, Sections 5.7.4.2-5.7.4.4.
Where specifics are not stated in AWWA D100, I would assume the API-650 requirements were generally intended or acceptable.
Then see Detail B in Figure 5.8 of API-650, which shows a tombstone-repad being shop-welded to the shell plate on the bottom side, without the fillet in between being connected to the bottom.

Thanks for feedback. That said, I'd still argue that even API 5.7.4.2-4 never mentions the "reinforcing plate" and only indicates the requirements of these sections as being applicable to the shell, an insert plate, or a thickened insert plate? API's definitions for insert plate and thickened insert plate are pretty specific in that they call them shell replacement plates. The engineer in me wants to require stress relieving after the reinforcing plate is put in place, but the owner's representative in me doesn't want to inadvertently add a bunch of costs to a project if it's not necessary.

Thanks again!

 

[JStephen]

Normally, the neck-to-shell weld would be made after the repad was in place.
In 5.7.4.4, certain welds are excluded (neck to flange, neck to internal pipe), but those welds have to be outside the reinforcing area. IE, neck-to-repad is not one of the welds that can be excluded.
Regardless, once you pre-assemble a shell plate and neck and stress-relieve it, there's not much reason to leave the repad until later- shop welding is generally cheaper than field welding.