×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Voids in SB-550 zirc bar

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?

RE: Voids in SB-550 zirc bar

Just looked at SB-550:  your bar could be a trimmed casting, with little or no hot-work vigorous enough to forge defects shut.  It is probable that you have run into a "shrink tree".  Are the discontinuities rounded, long and branching?

Other possibility is a true lamination:  dross/slag got included inside the bar during pouring & rolling.

RE: Voids in SB-550 zirc bar

(OP)
It looks like I'm not going to get to see any pictures. But the people who saw them said they were not laminations. So shrinkage does seem like the best explanation. I recognize that SB-550 does not explicitly require hot-work, but I would have thought that this would be required for any boiler code 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?
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources