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