×
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

stud wobble test

stud wobble test

stud wobble test

(OP)
Project involves a 1 1/2" x 8tpi steam turbine stud and its fitment to the internal threads of the turbine casing horizontal joint flange.  In defining the acceptability of the internal flange studs we would be looking to insert the stud into the flange a distance of 1 times the thread diameter.  We would look to indicate the movement of the stud by dial indicator method.  We anticipate that the acceptance criteria would be something less that .008" movement.  The question would be at what distance from the flange would the indication of the stud movement be taken?

RE: stud wobble test

How did you arrive at your acceptance criteria without this distance?

Movement of a male thread in its female hole is largely determined by the thread geometry and fit class.

Rather than trying to inspect in an acceptable condition after everything is built and assembled, why not take the time to properly identify what thread you need, and guage the parts at their points of manufacture rather than at assembly in the field.

RE: stud wobble test

I believe that the Westinghouse large steam turbine division at one time issued a Technical Advisory on turbine governor and throttle valve stud wobble tests. These tests were recommended to evaluate the extent of thread deterioration in the stud holes of castings.

We had performed such tests on valve studs and typically measured the extent of wobble by hand or with a straight edge off of the gasket surface. If any wobble was detected, it was cause for possibly enlarging the stud hole (as permitted by analysis to assure adequate ligament spacing between stud holes) and using mushroom type valve studs.

For HP and IP turbine shell mounting studs, we typically do not measure wobble because it is difficult to remove the studs that are threaded into the lower shell.

RE: stud wobble test

(OP)
Thank You Metengr for your comments.  In this instance the studs are remomved.  This is a Westinghouse unit.  Both GE and Westinghouse had Technical Advisory on the extent that they considered the internal stud threads acceptable, although the diction was vague.  In this case the existing stud has been removed.  The test is done in the effort to define the effect of any loss of material from the internal threads with the use of a new replacement stud.  If determined that the stud hole is unacceptable there is the possibility of oversizing the hole and going to a bottle design stud, or oversizing the hole, manufacture and installing a bushing, and using the original stud design.  I believe the acceptance criteria I mentioned was based on the measurement taken with the stud installed and the indication point being 1 1/2" (stud diameter) above the shell flange surface.  Any thoughts?

RE: stud wobble test

On a 1.5" diameter turbine shell stud, inserted into the shell and hand tight, the deflection can be measured along any point off the flange surface. Frankly, I think if you can feel any wobble by hand, this would be an indicator that the threads need to be chased or an insert should be considered.

Your 0.008" deflection seems too restrictive for stud hole threads on large steam turbine shells.

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