Voids in SB-550 zirc bar
Voids in SB-550 zirc bar
(OP)
Machining uncovered some large internal flaws in SB-550 zirc bar, 4.5" diameter round. These flaws are several inches long and almost one-eighth inch in width. Is this normal? To my mind, "bar" implies hot-rolling which would squeeze out voids this size.
The scary part is that I had planned on making this into a pressure vessel without UT. Hollow cylindrical parts up to NPS 4 can be machined from bar with no UT according to UG-14 / code case 2148. Beyond NPS 4, UT is required by code case 2156. So based on that, I had naively waived UT.
I'm eating crow and doing UT now, so the immediate problem is solved. But I'd like to figure out where I took a wrong turn. Did we get bad material, or did I miss a UT requirement in the code, or is this just something that designers are supposed to know?
The scary part is that I had planned on making this into a pressure vessel without UT. Hollow cylindrical parts up to NPS 4 can be machined from bar with no UT according to UG-14 / code case 2148. Beyond NPS 4, UT is required by code case 2156. So based on that, I had naively waived UT.
I'm eating crow and doing UT now, so the immediate problem is solved. But I'd like to figure out where I took a wrong turn. Did we get bad material, or did I miss a UT requirement in the code, or is this just something that designers are supposed to know?





RE: Voids in SB-550 zirc bar
Other possibility is a true lamination: dross/slag got included inside the bar during pouring & rolling.
RE: Voids in SB-550 zirc bar
This seems like a hole in the code. If cast billet is a permitted material, then it seems like volumetric inspection of billets should always be required. In paragraph UG-14, why is the NPS 4 phrase enclosed in square brackets? Does that have something to do with it?